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Model Electronic Railway Group

Leading Model Railway Electronics since 1967

Over 50 years of Innovation: 1967-2018

Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Copyright for items on this page is retained by the authors identified.

The use or misuse for the sale, design, supply, process, installation, delivery, test, repair, servicing, and alteration of the designs, instructions, computer code, photographs, circuits, and any other information that appear on this web site is entirely at the risk of the user or visitor to the web site. The information is made available in good faith strictly on the basis that no liability will attach to the Model Electronic Railway Group (MERG), its officers and members.

AC Alternating Current - Generally with a sinusoidal wave form. Mains power in Britain and Europe is 230v AC at 50Hz, that is 50 complete cycles per second. USA uses 115v at 60Hz.

Links:
http://www.allaboutcircuits.com/vol_2/chpt_1/1.html
AJC
Updated: Jan-2006
Accessory decoders DCC decoders are used to control trackside accessories such as turnouts and signals using the NMRA standard pulsed signal. The signal can be arried by the track and track feeders or can be a separate circuit, which avoids the risk of a derailment or short reventing the control of the turnouts.
All DCC manufacturers make accessory decoders and MERG provide kits.

Links:
http://www.merg.org.uk/merg_resources/acc2btxt.PDF
AJC
Updated: Jan-2006
Accessory encoder The MERG DCC accessory system is designed to be independent of the track DCC although it uses the NMRA Standard for its information encoding.


Links:
http://www.merg.org.uk/merg_resources/ace2btxt.PDF
AJC
Updated: Jan-2006
Address Address is the unique identification of anything. In the context of DCC it means the coding of each loco or other decoder, which ensures that it identifies the signals intended for it. AJC
Updated: Jan-2006
Amplifier An Amplifier is a device which uses a small amount of power to control a source of a large amount of energy. AJC
Updated: Jan-2006
Amplitude modulation (AM) The process of additively mixing a single or number of frequencies with the carrier wave to produce a complex waveform with variable amplitude. This signal may be demodulated by a simple diode detector. Most common method for low, medium and high frequency broadcast transmissions. Ron Mitchell
Amps The unit of current. It is defined as the constant current which if maintained in two straight parallel conductors of infinite length, of negligible cross-section and placed one metre apart in vacuum, will produce between the conductors a force equal to 2x10-7newton per metre length. AJC
Updated: Jan-2006
Analogue A continuously variable signal. This is generally compared to a digital signal, which increases in steps or is conveyed by digital coding. AJC
Updated: Jan-2006
And This is a Boolean operator which is used to join two statements so that the final statement is true only if the individual statements are all true. Thus (X>1)AND(X<2) is true if X is between 1 and 2. In electronic logic circuits an AND circuit is shown - AJC
Updated: Jan-2006
API Application Program Interface - A set of routines / protocols and tools for building software applications.

Links:
http://en.wikipedia.org/wiki/API
AJC
Updated: Jan-2006
Aspect The name given to the appearance of a signal to the driver of a train. Each aspect is allocated a specific meaning so that the driver can decode the message and react accordingly. For example a semaphore home signal has two aspects, one with the arm horizontal meaning stop and one with the arm inclined meaning proceed. KN
Updated: Jan-2006
Auto reverse An auto reverse module is used in DCC to prevent shorts in reversing loops and other situations where the polarity of two lines must be reversed for a train to run through. It works by reversing the polarity if a short is detected. If the short is eliminated then the new polarity is accepted and is kept. One auto reverse module can protect several track sections provided that only section break is being bridged by a loco at any one time. AJC
Updated: Jan-2006
AWG American Wire Gauge- This is not the same as Standard Wire Gauge. There is no direct conversion in that the ratio of radii SWG/AWG varies from 0.8 at 6/0 to 1.64 at 43.

Links:
http://www.hardwarebook.net/table/AWG.html

http://www.simetric.co.uk/siwire.htm
AJC
Updated: Jan-2006
Back EMF Back EMF generally refers to the voltage that will appear across an inductor if the current is stopped suddenly and in particular to the voltage generated by the rotation of a motor. In the latter case the voltage acts to reduce the current driving the motor so that the power consumed gets less as the speed rises to that speed at which the BEMF is equal to the applied voltage. If the BEMF exceeds the applied voltage the current will be reversed and the motor will be acting as a generator. This effect can be used to provide braking and at the same time recover energy. Some controllers use the BEMF to provide a measure of the speed of the motor. There must, of course, be nulls, periods when no voltage is applied, so that the BEMF can be measured while there is no current flowing; this is not synonymous with PWM. This comparative speed measurement can then be used to provide feedback to the controller in order to ensure a constant speed. AJC
Updated: Jan-2006
Baud Most people use baud to describe modem speeds in bits per second--but they are wrong. They may say a 9,600-bps modem transmits at 9,600 baud, but really baud is a measure of how frequently sound changes on a phone line. Modern modems transmit more bits with fewer changes in sound, so baud and bps numbers are not equal. However, only editors, pedants, and communications engineers now care about the distinction. But if you run into members of these groups, use bps instead of baud.

Links:
http://www.cnet.com/Resources/Info/Glossary/Terms/baud.html
AJC
Updated: Jan-2006
BC3 The BC3 is an automatic block control system. It controls the speed of a model train depending on the occupation of the block ahead. If the block ahead is uccupied the train will slow to a creep speed and stop at a designated point. Otherwise the train will accelerate to a preset speed. Manual control is also allowed for. Kits for the BC3 and literature about it is available from MERG - TBs T33/0-20.
The BC3 kit is No38 Nos 39 and 40 are a test jig and a setting up kit. Kit instructions for 38 and 39 are available from MERG.

Links:
http://www.merg.info/Members/tb.htm#T

http://www.merg.info/Members/kits.htm
http://www.merg.info/Members/kits/kitinstructions.htm
AJC
Updated: Jan-2006
Bell signals Bell Signals were used to convey information from between signal boxes.

Links:
http://www.signalbox.org/block/bells.shtml
AJC
Updated: Jan-2006
Bipolar Bipolar transistor - presumably not bipolar disorder or manic depression. AJC
Updated: Jan-2006
Bistable A Bistable is a circuit with two stable conditions so that it can be switched between the one and the other and hold it indefinitely. AJC
Updated: Jan-2006
Block Control Block control is the philosophy that a railway should be divided into blocks and that no train should normally be allowed to enter a block which is already occupied. This means that each block has a stop signal at which a train is required to wait if the block ahead is occupied. This will be set back 0.25 mile from the start of the next block. Further back there will be a distant signal which informs the driver that he needs to slow because the signal ahead is at stop.
Modern electric signalling systems allow for more variation in slow signals with the a double yellow as a preliminary caution as well as the yellow caution to give two stages of slowing.

Links:
http://www.signalbox.org/block.shtml
AJC
Updated: Jan-2006
Block occupancy Block Occupancy (The ToTI of the real railways) is detected by the electric track circuit which detects the presence of a train by conduction between the rails via the wheels. In the past some leading turnouts had a lock which was applied by a treadle on the near approach which applied a local mechanical lock when it was depressed by the passage of wheels. AJC
Updated: Jan-2006
BloNg BloNg (Block Oriented N-Gauge) controller was the original automatic block controller developed by the South-West Area Group of the N-Gauge Society. The BC3 resulted from a collaboration between the SW Area Group and the Oxford MRS, who also model in 00. The BC3 now replaces the BloNg controller, with which it is electrically compatible.
Exeter N Gauge Railway Modellers: Members each bring their own modules to be set up during the morning. Modules feature BloNg control and intermodule track adjusters as described in the N Gauge Journal.

Links:
http://www.merg.org.uk/merg_resources/blong/superbloc2.html

http://www.ngaugesociety.com/index.php?page=area-groups
AJC
Updated: Jan-2006
Boolean Boolean logic is the convention used in mathematics and circuitry for digital decision making. These are written as a statement which can be TRUE or FALSE. These statements can be joined by Boolean operators to form more complex statements which also are TRUE or FALSE. These statements have their parallels in electronic logic where the conditions of TRUE or FALSE are represented by the presence or absence of voltage and the operators are integrated chips.
There is nowhere in Boolean for MAYBE or DON'T KNOW.

Links:
http://www.ithacalibrary.com/sp/subjects/guide.php?subject=boolean
AJC
Updated: Jan-2006
Booster A Booster in DCC is a second power supply to increase the power available from the main master power supply. This may also have the facility for voltage inversion to allow for reverse loops etc but this is more cheaply handled by a specific reversing module. It can also help to reduce potential damage and problems by being used to divide the whole layout into separate sections each supplied by a booster so that shorts in one section do not affect another and the potential current is reduced to that available from one booster. AJC
Updated: Jan-2006
Bps In telecommunications and computing, bit rate (sometimes written bitrate or Rbit) is the number of bits that are conveyed or processed per unit of time. In digital multimedia, bit rate is the number of bits used per unit of time to represent a continuous medium such as audio or video. It is quantified using the bit per second (bit/s) unit or some derivative such as Mbit/s.
While often referred to as "speed", bit rate does not measure distance/time but quantity/time, and thus should be distinguished from the "propagation speed" (which depends on the transmission medium and has the usual physical meaning).
Wikepedia / John Ferguson
Updated: Jun-2006
Bridge rectifier A diode bridge (occasionall called a Graetz bridge)is an arrangement of four diodes connected in a bridge circuit as shown below, that provides the same polarity of output voltage for any polarity of the input voltage. When used in its most common application, for conversion of alternating current (AC) input into direct current (DC) output, it is known as a bridge rectifier. The bridge recitifier provides full wave rectification from a two wire AC input (saving the cost of a center tapped transformer) but has two diode drops rather than one reducing efficiency over a center tap based design for the same output voltage.
Diagram of bridge rectifier.
The diagram shows the operation of a bridge rectifier as it converts AC to DC. Notice how alternate pairs of diodes conduct.
Bridge examples
Wikepedia/ John Ferguson
Updated: Jun-2006
Buffer In computing, a buffer is a region of memory used to temporarily hold output or input data, comparable to buffers in telecommunication. The data can be output to or input from devices outside the computer or processes within a computer. Buffers can be implemented in either hardware or software, but the vast majority of buffers are implemented in software. Buffers are used when there is a difference between the rate at which data is received and the rate at which it can be processed, or in the case that these rates are variable, for example in a printer spooler.
The difference between buffers and cache:
Buffers are allocated by various processes to use as input queues, etc. Most of the time, buffers are some processes output, and they are file buffers. A simplistic explanation of buffers is that they allow processes to temporarily store input in memory until the process can deal with it.
Cache is typically frequently requested disk I/O. If multiple processes are accessing the same files, much of those files will be cached to improve performance (RAM being so much faster than hard drives), it's disk cache.
Wikepedia / John Ferguson
Updated: Jun-2006
Bus An electrical bus (sometimes spelled buss) is a physical electrical interface where many devices share the same electric connection. This allows signals to be transferred between devices (allowing information or power to be shared). A bus often takes the form of an array of wires that terminate at a connector which allows a device to be plugged onto the bus.
  • Buses are used for connecting components of a computer: a common example is the PCI bus in PCs. See computer bus.
  • Buses are used for communicating between computers (often microprocessors). See computer bus.
  • Buses are used for distribution of electrical power to components of a system. The (usually) thick conductors used are called busbars. In an electrical laboratory, for example, a bare bus-bar will sometimes line the wall, to be used by the engineers and technicians for its high electrical current carrying capacity, which allows a convenient approximation to zero voltage, or ground in the US, and earth in the UK.
In analysis of an electric power network a "bus" is any node of the single-line diagram at which voltage, current, power flow, or other quantities are to be evaluated. These may or may not correspond with heavy electrical conductors at a substation.
Wikepedia/ John Ferguson
Updated: Jun-2006
C/MRI Bruce Chubb's Computer/Model Railroad Interface system C/MRI. A series of modules and support available for the system obtained from JLC Enterprises Inc.
For website see links page
JLC Enterprises Inc. / John Ferguson
Updated: Jun-2006
Cab Control A system of control using DC power where more than one controller or cab is used to drive trains across the tracks controlled by another controller. This requires switches to transfer the supply from the cabs to the parts of the layout they will control, the switches preventing two or more cabs controlling simultaneously the same section of track. John Ferguson
MERG Secretary
Updated: Jun-2006
Cabling Referto MERG TB on layout cabling LC01 (Note available to members only) MERG TB / John Ferguson
Capacitor A capacitor can store electric energy when disconnected from its charging circuit, so it can be used like a temporary battery. Capacitors are commonly used to supply energy to electronic devices without the memory being lost when changing their batteries.
Capacitors are used in power supplies where they smooth the output of a full or half wave rectifier. They can also be used in charge pump circuits as the energy storage element in the generation of higher voltages than the input voltage.
Capacitors are connected in parallel with the power circuits of most electronic devices and larger systems (such as factories) to shunt away and conceal current fluctuations from the primary power source to provide a "clean" power supply for signal or control circuits. Audio equipment, for example, uses several capacitors in this way, to shunt away power line hum before it gets into the signal circuitry. The capacitors act as a local reserve for the DC power source, and bypass AC currents from the power supply.
Capacitors may retain a charge long after power is removed from a circuit; this charge can cause shocks (sometimes fatal) or damage to connected equipment. For example, even a seemingly innocuous device such as a disposable camera flash unit powered by a 1.5 volt AA battery contains a capacitor which may be charged to over 300 volts. This is easily capable of delivering an extremely painful, and possibly lethal shock.
Hazard Warning
Many capacitors have low equivalent series resistance (ESR), so can deliver large currents into short circuits, and this can be dangerous. Care must be taken to ensure that any large or high-voltage capacitor is properly discharged before servicing the containing equipment. For safety purposes, all large capacitors should be discharged before handling. For board-level capacitors, this is done by placing a bleeder resistor across the terminals, whose resistance is large enough that the leakage current will not affect the circuit, but small enough to discharge the capacitor shortly after power is removed. High-voltage capacitors should be stored with the terminals shorted to dissipate any stored charge.
Wikepedia / John Ferguson
Carlos A computer programme for creation of model railway control panels on screen. Carlos is a DOS program developed by MERG member John Down and can be used with the RPC system. See TB G18/1 or follow this link for more information. MERG TB
CDU Its short for capacitor discharge unit (CDU). Its use is generally to store a high voltage charge which is released very quickly to kick start solenoid operated point motors. MERG Secretary
John Ferguson
Updated: Jun-2006
CE The CE mark (officially CE marking) is a mandatory marking on certain products, which is required if they are placed on the market in the European Economic Area (EEA). By affixing the CE marking, the manufacturer, or its representative, or the importer assures that the item meets all the essential requirements of all applicable EU directives. Examples of European Directives requiring CE marking: Toys-, Machinery-, Low Voltage equipment-, R&TTE-, EMC-Directive. There are about 25 Directives requiring CE marking.
Wikepedia / John Ferguson
Updated: Jun-2006
Ceramic The word ceramic is derived from the Greek word κεραμικος (keramikos, "having to do with pottery"). The term covers inorganic non-metallic materials whose formation is due to the action of heat.
This can refer to the packaging of integrated circuits in a ceramic material.
Wikepedia
MERG Secretary
John Ferguson
Updated: Jun-2006
Channel Programmable 4 - channel Servo Driver Type ‘Servo4’ For operation of model railway accessories such as turnouts and semaphore signals. The word channel refers to the ability to control 4 devices.
See the MERG newsletter (now called a Journal) of March 2006 pages 8 and 9 on the web site.
MERG member
Mike Bolton
Updated: Mar-2006
Charlieplexing Charlieplexing is a method of matrix multiplexing which uses each wire in turn as the sink.
See the MERG newsletter (now called a Journal) of March 2006 pages 34 and 35 on the web site.
MERG Member Archie Campbell
Updated: Mar-2006
Circuit An electrical circuit is a network that has a closed loop, giving a return path for the current and usually connecting a series of electrical components. MERG Secretary John Ferguson
Updated: Jun-2006
Cleaning Tracks There is a commercial product called Relco. More information on cleaning tracks can be obtained from Southern E-Group web site.

Links:
http://freespace.virgin.net/c.gardner/semg/relco.htm
MERG Secretary
John Ferguson
Updated: Jun-2006
Clearing point This is a location in advance of a signal box up to which the track must be clearto allow a signalman to accept a train into a block section.
See the MERG newsletter (now called a Journal) of March 2006 pages 23 on the web site.
MERG Member
Dave Roberts

Updated: Mar-2006
Clock In electronics and especially synchronous digital circuits, a clock signal is a signal used to coordinate the actions of two or more circuits. A clock signal oscillates between a high and a low state, normally with a 50% duty cycle, and is usually a square wave. Circuits using the clock signal for synchronization may become active at either the rising or falling edge, or both.
A crystal oscillator is often used in electronic circuits (sometimes abbreviated to XTAL on schematic diagrams) This uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. This frequency is commonly used to keep track of time (as in quartz wristwatches), to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio transmitters.
Using an amplifier and feedback, it is an especially accurate form of an electronic oscillator. The crystal used therein is sometimes called a "timing crystal".
Wikepedia / John Ferguson
Closed loop To avoid the problems of the open-loop controller, control theory introduces feedback. A closed-loop controller uses feedback to control states or outputs of a dynamical system. Its name comes from the information path in the system: process inputs (e.g. voltage applied to a motor) have an effect on the process outputs (e.g. velocity or position of the motor), which is measured with sensors and processed by the controller; the result (the control signal) is used as input to the process, closing the loop. Wikepedia / John Ferguson
Updated: Jun-2006
CMOS CMOS ("see-moss"), which stands for complementary metal-oxide semiconductor, is a major class of integrated circuits. CMOS chips include microprocessor, microcontroller, static RAM, and other digital logic circuits. The central characteristic of the technology is that it only uses significant power when its transistors are switching between on and off states. Consequently, CMOS devices use little power and do not produce as much heat as other forms of logic. CMOS also allows a high density of logic functions on a chip.
The word "complementary" refers to the fact that the design uses pairs of transistors for logic functions, only one of which is switched on at any time.
The phrase "metal-oxide-semiconductor" is a reference to the nature of the fabrication process originally used to build CMOS chips. That process created field effect transistors having a metal gate electrode placed on top of an oxide insulator, which in turn is on top of a semiconductor material. Instead of metal, today the gate electrodes are almost always made from a different material, polysilicon, but the name CMOS nevertheless continues to be used for the modern descendants of the original process.
Wikepedia / John Ferguson
Updated: Jun-2006
Coil In electrical engineering, an electromagnetic coil is formed when a metallic or conductive wire is looped around a core to create an electronic inductor or electromagnet. One loop of wire is usually referred to as one turn. A coil consists of one or more turns. For use in an electronic circuit, electrical connection terminals called taps are often connected to a coil. Coils are often coated with varnish and/or wrapped with insulating tape to provide additional insulation and secure them in place. A completed coil assembly with taps etc. is often called a winding. A transformer is an electromagnetic device that has a primary winding and a secondary winding that transfers energy from one electrical circuit to another by magnetic coupling without moving parts. The term tickler coil usually refers to a third coil placed in relation to a primary coil and secondary coil. Wikepedia / John Ferguson
Updated: Jun-2006
Colour light Refers in model railways to model signals with coloured LED lights for red, amber, and green. MERG Secretary
John Ferguson
Updated: Jun-2006
Com port In computer hardware, a port serves as an interface between the computer and other computers or devices in the form of an electrically wired outlet on a piece of equipment into which a plug or cable connects. These hardware ports have different physical shapes such as male, female, round, rectangular, square, oblong, etc. There is some standardization to physical properties and function. For instance, most computers have a keyboard port (currently round, or telephone type), into which the keyboard is connected.
Hardware ports can almost always be divided into two groups:
  • Serial ports send and receive one bit at a time via a single wire pair (Ground and +/-).
  • Parallel ports send multiple bits at the same time over several sets of wires.
A Software Port (usually just called a 'port') is a virtual data connection that can be used by programs to exchange data directly, instead of going through a file or other temporary storage location. The most common of these are TCP and UDP ports which are used to exchange data between computers on the Internet.
Wikepedia / John Ferguson
Updated: Jun-2006
Command station The Command Station is the brains of a DCC system of control and is in control of the whole system. After receipt of requests from one or several cabs or throttles, the command station’s internal computer translates these cab requests into decoder commands in the form of digital packets. These are received via the track in the decoders fitted in locomotives or other accessory decoders such as the type used to control points and signals.
Common A wire or connector that is Common or connected to all the components of a circuit.
Common Return Wiring Is one way of wiring a model railway with less wires
Individual supply common return wiring

Links:
http://rail.felgall.com/crw.htm

Computer Control Software Software designed specifically to control the activities of a model railway. Can provide a visual indication on the computer screen of every aspect of the control system. There are commercial software systems available as well as software developed by MERG members.
Conductor Conductors are materials that allow electrical charges to flow through them. They are the opposite of insulators. Also see semi-conductor.
Control Systems A Control System as applied to model railways can be any system that controls the activities of the railway.
Crystal Oscillator that uses a quartz Crystal in its feedback path to maintain a stable output frequency.
CSA Believed to be an out dated method of assessment overtaken by the CE marking on products.
Current Electric current is by definition the flow of electric charge. The SI unit of electric current is the ampere (A)
Measured in amperes, it is the flow of electrons through a conductor. Also know as electron flow.

Current shunt In electronics, a Current Shunt is a device which allows electrical current to pass around another point in the circuit.
CVs A CV is a configuration variable that is a characteristic of a DCC decoder that can be customised by the user. CV’s are defined by the NMRA. For example the address of a locomotive is located in CV1. Significant modifications can be made to the performance of a locomotive by changing the CV’s.
D type connector A D type connector is usually with 9 or 25 pins to connect computer cables. It is in two parts. A socket or female connector and a male plug. It is known as a D type connector due to the D shape of the surround to the pins and socket.
DC Control DC or direct current, usually from a 12v supply, is the traditional method of controlling and powering model locomotives by varying the voltage supplied to the track.
DCC Digital Command Control DCC Digital Command Control systems, both analogue and digital, allow you to simulate prototypical train operation on your model railroad. With Digital Command Control you can operate multiple locomotives independently at the same time on the same section of track without a computer and without blocking or other complex wiring schemes. Digital Command Control systems use digital data packets to communicate commands to decoders that control locomotives and turnouts on the railroad.
What will it do for me and my railroad?
Simply put, DCC will let you "run your trains, not your track." DCC gives you the freedom to bring your railroad to life! With DCC you have truly prototypical operation at your fingertips.
Why use a digital system rather than an analoge system?
Because digital technology gives extremely reliable operation and the technology is almost infinitely extendable without causing backward compatibility problems (analoge systems are inherently more restrictive). Also, digital systems make wiring simple and easy to install. Because a digital system encodes information sent from the command station to the decoder as numbers grouped into packets, new types of packets can be added to a digital system to send more information thus extending the existing system without causing backward compatibility problems.

DecoderPro A better tool for programming decoders. DecoderPro simplifies the job of configuring complicated DCC decoders by providing screens on which you can select the various options and values you want.
Modern DCC decoders are complicated beasts to program. The simple idea of "put the address in CV01" doesn't cope well when you program complicated functions using combinations of bit patterns. A friendlier interface is needed. There are programs that provide better ways of programming specific decoders. Unfortunately, they are limited to specific types of computers, and only their authors can customize them for new types of decoders.
The DecoderPro symbolic programmer is meant to improve this. It is configured using text files, so that it can be adapted to additional decoder types easily. It talks to the decoders using the JMRI programming interface, so that it can run on any computer and layout hardware that JMRI has been ported to. It's freely available for download. And since the code is available via open source, if you want to improve on it you can.

Links:
http://jmri.sourceforge.net/help/en/html/apps/DecoderPro/index.shtml

Decoupling capacitor Decoupling capacitors are used to prevent transfer of high-frequency noise between electrical nodes. The most common use of decoupling capacitors is on power supply rails where they prevent voltage drop when transient voltage spikes/current spikes are experienced. These capacitors can be viewed as small localized energy reservoirs.
Digital The word digital is most commonly used in computing and electronics, especially where real-world information is converted to binary numeric form as in digital audio and digital photography. Such data-carrying signals carry either one of two electronic or optical pulses, logic 1 (pulse present) or 0 (pulse absent). The term is often meant by the prefix "e-", as in e-mail and ebook, even though not all electronics systems are digital.
Digitrax Digitrax is a sullpier of DCC systems located in Norcross, Georgia (just outside Atlanta).
They supply a full range of command stations, decoders and accessories.
For website see links page

DIL Dual in line sockets DIL. A socket usually plastic for soldering to a printed circuit board to receive the pins of a computer chip.
Diode The DIODE is an electronic component that allows the passage of current in only one direction. They are solid state semiconductor devices and typically need more than 0.6 volts to operate. In a normal diode, current flows from the positive anode to the negative cathode. Early diodes were in reality, vacuum-tube rectifiers, consisting of an evacuated glass or steel envelope containing two electrodes—a cathode and an anode. Because electrons can flow in only one direction, from cathode to anode, the vacuum-tube diode could be used as a rectifier. That is still a use of diodes in today's electronic circuits; now they are all semiconductor diodes. The simplest of these, the germanium point-contact diode, dates from the early days of radio, when the received radio signal was detected by means of a germanium crystal and a fine, pointed wire that rested on it. In modern germanium (or silicon) point-contact diodes, the wire and a tiny crystal plate are mounted inside a small glass tube and connected to two wires that are fused into the ends of the tube. Junction-type diodes consist of a junction of two different kinds of semiconductor material. There are literally thousands of different specification diodes. They are usually identified with a number but some are colour coded. You can use our Diode Colour ID Band Table to identify such diodes.
The Zener diode is a special junction-type diode, using silicon, in which the voltage across the junction is independent of the current through the junction. Because of this characteristic, Zener diodes are used as voltage regulators. (Try our Zener Diode Calculator.) Another special junction-type diode is used in solar cells; a voltage appears spontaneously when the junction is illuminated. In light-emitting diodes, commonly called LEDs, the exact opposite happens. A voltage applied to the semiconductor junction results in the emission of light energy. LEDs are used in numerical displays such as those on electronic digital watches and pocket calculators. They are usually in one of two shapes, bars or dots, and come in various sizes. Bars are placed in a particular pattern to form letters or numbers; when they are letters, they are called an alpha display. When the are numbers, they are called a numeric display. In many cases, they can be either and are known as an alpha-numeric display.

DPDT Double Pole Double Throw (DPDT) switch. A switch which connects or disconnects two inputs to two sets of outputs
DPR DPR Double Pole Relay - In spite of all the advances in electronic components over the past few years, there is still no realisticalternative to the electro-mechanical relay. This is especially the case when the voltages or currents to be
switched bear no relation to the circuitry switching them. Similarly, the ‘Changeover Switch’ arrangement is not
easy (or economical) to implement in solid state form. Analogue Switches are available, but are generally only
suitable for ‘small signal’ circuitry such as Audio/Video equipment.
The module shown here provides eight independent double pole changeover relays, mainly intended
for track section switching, frog polarity switching etc, although they can be used for any desired function within
the specification of the relays. The module is designed to be Control Panel mounted, as part of an RPC (remote panel control) system by a MERG member.

DPST Double Pole Single Throw (DPST) A switch that connects or disconnects one input to one output.
Driver This a system to get computer programs to work the hardware to work the track/locos signals MERG Member
Brian Johnson
Updated: Jul-2006
Electro frog Is a Peco term for live (power) frog Turnout (Switch or Points),which some people call power-routing.

Peco electro-frog

Links:
http://www.loystoys.com/peco/about-electrofrog.html
PECO
Updated: Jul-2006
Electro magnet A coil of wire in air or on a former that if current is passed through the wire a magnetic field will be produced

Electro-magnet

Links:
http://www.le.ac.uk/se/centres/sci/selfstudy/mam11.htm
MERG Member
Brian Johnson
Updated: Jul-2006
Faller Manufacture Model Railway accessories and buildings. Faller road system MERG TBA36/1&/2 - merg members only
MERG Member
Brian Johnson
Updated: Jul-2006
Fast clock Is use in time table model railway operation where the time goes faster
There is a MERG TB A32/2 MERG kit for members
MERG Member
Brian Johnson
Updated: Jul-2006
Feathers Term used for the 'route indicator' on colour light signals comprising 5 white lights at an angle to indicate the diverging route. MERG Member
Keith Norgrove
Updated: Jun-2008
Fets The field effect Transistor is a device which us to use one electrical signal to control another. The name ‘transistor is a shortened version of the original term transfer resistor, which indicates how the device works. Most transistors have three connections. The voltage on (or current into/out of) one wire has the effect of controlling the ease with which current can move between the other two terminals. The effect is to make a resistance whose value can be altered by the input signal. We can use this behaviour to transfer patterns of signal fluctuation from a small input signal to a larger output signal.
MERG TB G12/1 - merg members only

Links:
http://www.st-andrews.ac.uk/%7Ewww_pa/Scots_Guide/first11/part7/page1.html
MERG Member
Brian Johnson
Updated: Jul-2006
Flip flop “Flip Flop” is the common name given to a two-stage device, which offer basic memory for sequential operation. Flips flops are heavily used for digital data transfer and are commonly used in banks called “registers for the storage of binary numerical data.

Links:
http://en.wikipedia.org/wiki/Flip-flop_%28electronics%29
Wikepedia
Updated: Jun-2006
Frequency Frequency is the measurement of the number of times that a repeated event occurs per unit of time.

Links:
http://en.wikipedia.org/wiki/Frequency
Wikepedia
Updated: Jun-2006
Frequency modulation (FM) The process of varying the carrier frequency with the modulation frequency thus enabling the signal to have a constant amplitude, mainly used at Very High Frequencies 90-110MHz broadcasts, this enables verygood noise control. More complex than AM as it requires a special demodulator to obtain the information. Ron Mitchell
Fuse This a protection device to protect the main power, or any type of supply

MERG Member
Brian Johnson
Updated: Jul-2006
GPP software This is a company that has written a Microsoft Basic program to control a model railway from a computer.

Links:
http://www.gppsoftware.com
MERG Member
Brian Johnson
Updated: Jul-2006
Ground Is a common point in circuits normally 0 volts, but can be higher than 0 volt.
MERG Member
Brian Johnson
Updated: Jul-2006
Hall effect This a transistor type that is effected by a magnetic field placed in close proximity
See MERG TBs A7/2/ 3/ 4 merg members only
MERG Member
Paul King
Updated: Jul-2006
Handset DCC HandsetIs a means of control in your hand. MERG Member
Brian Johnson
Updated: Jul-2006
Header plug or socket Are plug & sockets primarily for use on PCB boards to make connections to and from the board

Typical header
MERG Member
Brian Johnson
Updated: Jul-2006
Heat sink Waste heat is produced in transistors due to the current flowing through them. Heat sinks are needed for power transistors because they pass large currents.
If you find that a transistor is becoming too hot to touch it certainly needs a heat sink!
The heat sink helps to dissipate (remove) the heat by transferring it to the surrounding air.

Typical heatsink

Links:
http://www.kpsec.freeuk.com/components/heatsink.htm
kpsec
Updated: Jun-2006
Hector This is a track detector using an optical system to detect the location of train Merg kit for members MERG Member
Bryan Knight
Updated: Jul-2006
High This what we call greater than the base voltage or ground e.g. so high is 5v ~ 4.4volts above 0 BJ
Updated: Jan-2007
HYPOTRAC This a high voltage track detector system for 2 rail Model railway track , see TB T9/2 merg members only Merg Member
John Dowm
Updated: Jul-2006
Hysteresis loop Hysteresis is wellknown in ferromagnetic materials. When an external magnetic field is applied to a ferromagnet, the ferromagnet absorbs some of the external field. Even when the external field is removed, the magnet will retain some field: it has become magnetized.

Links:
http://en.wikipedia.org/wiki/Hysteresis
Wikepedia
Updated: Jul-2006
ICs Integrated Circuits are usually called ICs or chips. They are complex circuits which have been etched onto tiny chips of semiconductor (silicon). The chip is packaged in a plastic holder with pins spaced on a 0.1"(2.54mm) grid which will fit the holes on stripboard and breadboards. Very fine wires inside the package link the chip to the pins.

Integrated circuits

Links:
http://www.kpsec.freeuk.com/components/ic.htm
kpsec
Updated: Jul-2006
Incandescent lamps Lamps emit light when an electric current passes through them. All of the lamps shown on this page have a thin wire filament which becomes very hot and glows brightly when a current passes through it. The filament is made from a metal with a high melting point such as tungsten and it is usually wound into a small coil.
Filament lamps have a shorter lifetime than most electronic components because eventually the filament 'blows' (melts) at a weak point.

MES lamplamp with wire tails

Links:
http://www.kpsec.freeuk.com/components/lamp.htm
kpsec
Updated: Jun-2006
Inductor An inductor is a coil of wire which may have a core of air, iron or ferrite (a brittle material made from(iron). Its electrical property is called inductance and the unit for this is the henry, symbol H. 1H is very large so mH and uH are used, 1000uH and 1000mH=1H.
Iron and ferrite cores increase the induction.
Inductors are mainly used to tune circuits and to block high frequency AC signals (they re sometimes called chokes)
They pass DC easily, but block AC signals ,This is the opposite to capacitor.

Inductor

Links:
http://www.kpsec.freeuk.com/components/other.htm#inductor
kpsec
Updated: Jun-2006
Infra red emitter These IR emitters are high intensity Gallium Arsenide infrared emitting diodes mounted in
clear plastic with a smoke color lens.
They are made with Gallium Aluminum Arsenide window layer on Gallium Arsenide Infrared emitting diodes. Viewing angle is 20 degrees

Infra red emitters
MERG Member
Brian Johnson
Updated: Jul-2006
Infra red receiver/detector Two types of IR receivers are used, a phototransistor or a photodiode

Photo-diode
MERG Member
Brian Johnson
Updated: Jul-2006
Insulfrog Description used by UK track manufacturer, PECO, to denote turnouts manufactured with an insulated crossing (frog). This avoids the need for polarity switching for the crossing at the expense of poorer current collection for locomotives. KN
Updated: Jan-2006
Interlocking Name for means of linking the operation of points and signals such that signals can only show a proceed aspect when points are correctly set, and that points cannot be moved unless the signals over them are showing stop aspects. Interlocking can be mechanical, electrical using relays or carried out by computers. KN
Updated: Jan-2006
Java This is a Software programming system by Sun Microsystems

Links:
http://java.sun.com

http://java.sun.com/docs/books/tutorial/
BJ
Updated: Jan-2007
JMRI Java Model Railroad Interface: The main information on this open source software initiative. There is a Yahoo Group providing support.

Links:
http://jmri.sourceforge.net/

http://groups.yahoo.com/group/jmriusers/files/
BJ
Updated: Jan-2007
Kits A set of parts and instruction to build something BJ
Updated: Jan-2007
Latching A pulse method to change the state from on to off or vice versa.


Links:
http://www.heathcote-electronics.co.uk/RelayBrd.htm

http://www.4qdtec.com/trd.html
BJ
Updated: Jan-2007
Lead free This is a change in the content of solder. It cannot have lead in it due to Health and Safety requirements BJ
Updated: Jan-2007
LED Light Emitting Diodes (LEDs) emit light when an electric current passes through them. Example:Red LED
Circuit symbol: LED symbol

Links:
/merg_resources/led.php

http://www.kpsec.freeuk.com/components/led.htm
BJ
Updated: Jan-2007
LENZ A German dcc system and decoder manufacturer BJ
Updated: Jan-2007
Lighting decoder A DCC decoder made especially for lights for a loco or carriages. BJ
Updated: Jan-2007
Logic In a model railway it is a way to do step by step sequence to make the train do what you require.

Links:
http://en.wikipedia.org/wiki/Logic
BJ
Updated: Jan-2007
Magnet A magnet is an object that has a magnetic field. It can be in the form of a permanent magnet or an electromagnet.

Links:
http://en.wikipedia.org/wiki/Magnet
BJ
Updated: Jan-2007
Microprocessor A microprocessor (sometimes abbreviated µP) is a programmable digital electronic component that incorporates the functions of a central processing unit (CPU) on a single semiconducting integrated circuit (IC).

Links:
http://en.wikipedia.org/wiki/Microprocessor
BJ
Updated: Jan-2007
Mobile decoder A DCC decoder intended for fitting in a loco. BJ
Updated: Jan-2007
Modulation Is the process of superimposing information onto a pure sine wave (Carrier wave), this process can be achieved by any of fourmethods, amplitude (AM), frequency (FM), Phase (PM)
or Pulse (PAM, PWM, or PPM)
Ron Mitchell
Multiplexor A communications device that multiplexes (combines) several signals for transmission over a single medium. A demultiplexor completes the process by separating multiplexed signals from a transmission line. Frequently a multiplexor and demultiplexor are combined into a single device capable of processing both outgoing and incoming signals.
A multiplexor is sometimes called a mux and also spelled as multiplexer.

Links:
http://www.webopedia.com/TERM/M/multiplexor.html
BJ
Updated: Jan-2007
Negative A DC term that means the voltage is lower than 0
You can have it plus or minus the zero point
BJ
Updated: Jan-2007
NMRA The National Model Railroad Association in the USA is the largest organization devoted to the development, promotion, and enjoyment of the hobby of model railroading. The NMRA was founded in 1935 in Milwaukee, Wisconsin in order to provide a service to the hobby of model railroading. It is responsible for defining the standards for DCC control systems. BJ
Updated: Jan-2007
NOR Nor is a gate term used to describe logic components.
NOR gate (NOR = Not OR)
This is an OR gate with the output inverted, as shown by the 'o' on the output.
The output Q is true if NOT inputs A OR B are true: Q = NOT (A OR B)
A NOR gate can have two or more inputs, its output is true if no inputs are true.

NPN Types of transistor: There are two types of standard transistors, NPN and PNP, with different circuit symbols. The letters refer to the layers of semiconductor material used to make the transistor. Most transistors used today are NPN because this is the easiest type to make from silicon. If you are new to electronics it is best to start by learning how to use NPN transistors.
See also: Transistors

Octal Darlington Arrays Circuit diagram of Darlington configuration
In electronics, the Darlington transistor is a semiconductor device which combines two bipolar transistors in tandem (often called a "Darlington pair") in a single device so that the current amplified by the first is amplified further by the second transistor. This gives it high current gain (written β or hFE), and takes up less space than using two discrete transistors in the same configuration. The use of two separate transistors in an actual circuit is still very common, even though integrated packaged devices are available.
Wikepedia
Updated: Jun-2006
Ohms Definition: >An ohm is a resistance that produces a potential difference of one volt when a current of one ampere is flowing through it.
1 ohm = 1volt/amp (1 Ω = 1 V/A
Wikepedia
Updated: Jul-2006
Op amp Operational amplifier Also called an op amp. A specialized linear integrated circuit (IC) that consists of several transistors, resistors, diodes, and capacitors, interconnected to produce gain over a wide range of frequencies. A single amplifier can comprise an entire IC, or an IC can contain several amplifiers. The dual op amp and the quad op amp are common variants. Some ICs contain one or more amplifiers in addition to other circuits. The devices can be used with resistance-capacitance (RC) network combinations to build active filters for use at audio frequencies. The Illustrated Dictionary of Electronics (4th Ed) Stan Gibilisco (Published by McGraw-Hill)
Open collector Open-collector configuration In an integrated circuit, an output scheme utilizing no internal pull-up resistor. Wired-OR outputs can thus have opposite states without risk of damage to the device. The Illustrated Dictionary of Electronics (4th Ed) Stan Gibilisco (Publishedby McGraw- Hill)
Optical detector Optical detector: Anintegrated-circuit (IC) that provides light-to-voltage conversion. Its direct-current output voltage is proportional to the intensity of light impinging on its sensor. The Illustrated Dictionary of Electronics (4th Ed) Stan Gibilisco (Published by McGraw-Hill)
Opto-isolator Optoisolator: A light-emitting diode (LED) or infrared-emitting diode (IRED) and a photodiode combined in a single package with a transparent gap between them. The LED or IRED converts an electrical signal to visible light or IR; the photodiode changes the visible light or IR back into an electrical signal. This device eliminates interstage impedance reflections that can plague systems that employ electronic coupling. Even the most drastic changes in load impedance have no effect on the impedance “seen” by the signal source.
The devices can also protect expensive equipment against electrical transients; for example, in telephone-line modems used with personal computers.
The Illustrated Dictionary of Electronics (4th Ed) Stan Gibilisco (Published by McGraw-Hill)
Oscillation Oscillation: The periodic change of a body or electrical quantity in amplitude or position (e.g., oscillation of a pendulum, voltage, or crystal plate). The Illustrated Dictionary of Electronics (4th Ed) Stan Gibilisco (Published by McGraw-Hill)
Oscilloscope An instrument thatpresents the pattern representing variations in an electrical quantity for visual inspection on a Cathode Ray Tube (CRT) The Illustrated Dictionary of Electronics (4th Ed) Stan Gibilisco (Published by McGraw-Hill)
Parallel 1 . Pertaining to the shunt connection of components or circuits.
2. Pertaining to the type of operation in a computer when all elements in an information item (e.g., bits in a word) are acted upon simultaneously, rather than serially (one at a time
3. The condition in which two comparably sized objects or figures are equidistant at all facing points parallel).
The Illustrated Dictionary of Electronics (4th Ed) Stan Gibilisco (Published by McGraw- Hill)
PCB software Software for producing the “Gerber” files which are used in the etching process to produce the required PCB’s Ron Mitchell
Peco motor The PECO implementation of the Point motor, notable because they are constructed so as to be directly attached to both N and 00 gauge PECO track, thus making it easier to line up the pull and throw of the point Ron Mitchell
Phase 1. The angular relationship between two points in time of a sine wave.
2. The angular relationship between two sine waves simultaneously.
Ron Mitchell
Phase Modulation (PM) A specialist modulation mainly used in Radar equipment, the phase rather than the frequency of the carrier wave is varied in order to obtain information Ron Mitchell
PIC A complex integrated circuit which may be programmed to carry out a controlled sequence of events, ie certain output events controlled by an input event Ron Mitchell
PMD1 A piece of electronic kit designed by Gordon Hopkins which may be used to switch fast action point motors See TB G16/14 From TB list
PMD2 A piece of electronic kit designed by Gordon Hopkins which may be used to switch slow action point motors See TB G16/15 From TB list
PMR1 Solenoid Point motor /relay driver with onboard relay see TBG16/26 From TB list
PNP A bipolar junction transistor in which the emitter and collector layers are p-type semiconductor material, and the base layer is n-type semiconductor material. See also "NPN" and "Transistor" The Illustrated Dictionary of Electronics (4th Ed) Stan Gibilisco (Published by McGraw-Hill)
Point Motors An electro mechanical device for switching points. There are many examples of point motors, some are fast solenoid switched and others slower acting motor switched Ron Mitchell
Points A track based device for manually or electrically switching one input track to two or more tracks, or two or more tracks into one track. Ron Mitchell
Polarity 1. The condition of being electrically positive or negative.
2. The condition of being magnetically north or south.
3. The orientation of the positive and negative poles in a battery or power supply relative to a circuit.
4. The orientation of a magnetic field, relative to the surrounding environment.
The Illustrated Dictionary of Electronics (4th Ed) Stan Gibilisco (Published by McGraw-Hill)
Positive 1. The condition of being electrically positive or negative.
2. The condition of being magnetically north or south.
3. The orientation of the positive and negative poles in a battery or power supply relative to a circuit.
4. The orientation of a magnetic field, relative to the surrounding environment.
The Illustrated Dictionary of Electronics (4th Ed) Stan Gibilisco (Published by McGraw-Hill)
Pot Abbreviation for Potentiometer see below
Potentiometer 1. A variable resistor used as a voltage divider. The input voltage is applied across the entire resistance element and the output voltage is taken from the wiper, relative to one end of the element. One end is usually grounded (at zero potential).
2. A null device whose operation is based on a variable resistor, and is used for precise voltage measurements. The unknown voltage is applied to the input of a variable resistor whose settings are known with great accuracy; the resistance is adjusted for an output voltage that exactly equals the voltage of a standard cell (as indicated by a null between the two voltages). The unknown voltage is then determined from the resistance and the standard-cell voltage.
The Illustrated Dictionary of Electronics (4th Ed) Stan Gibilisco (Published by McGraw-Hill)
Power district Power to the track is divided into sections. Can be to assist fault finding, to avoid shutting down the whole layout if a short occurs, and in large layouts to provide separate power supplies one to each district.
Power pack A controller including a power supply to the track.
Programming The activity of entering a list of instructions that a computer can act on. That is “run” the programme. These instructions take the form of a programming language that the computer can understand. John Ferguson
Progressive cab control The means to facilitate manually driven trains following one another on the same track but in different electrical sections powered by different controllers. (See MERG Journal August 2005 page 10) Mike Buckingham
PSU Power supply unit
PTP RPC System - PTP (Point-to-Point)
Self contained (non-PC) automatic data transfer system for up to 960 functions each way, using standard RPC Modules. Includes PCBs and all components.

Pulse Can be any shape and is normally a short period of time
Pulse Modulation There are basically 3 forms of pulse modulation, Amplitude, Position, and width, each having its own characteristics and uses. This type of modulation may be superimposed onto RF or on DC voltages. Ron Mitchell
Pulsed output Pulsed output duty cycles
QTU The QTU (Quad Throttle Unit) by Howard Amos is intended to be a throttle (controller) unit for use on a model railway. In fact four throttles are built into a single card. These four throttles can be used as conventional manual throttles by connecting potentiometers for speed and switches for brake and reverse. Inertia potentiometers can also be added so that speed changes are gradual. Track circuiting (current detectors) are built-in and these could be used to drive lights on a control panel. QTU kits are available as full kits and as partial kits containing just the hard to get parts. Only Howard Amos's Tcc software is currently (2008) capable driving QTU's. John Ferguson & Howard Amos
RC filter A resistance and capacitor network to limit a particular frequency
Or noise rejection from motors

Rectification The process of converting alternating current (AC) to direct current (DC). most offten using diodes. The diodes are commonly arranged in a set of 4 combined in one package. See also "Bridge rectifier".
Reed Switch The contacts of a reed switch (usually SPST) are closed by bringing a small magnet near the switch. They are used in security circuits, for example to check that doors are closed. Standard reed switches are SPST (simple on-off) but SPDT (changeover) versions are also available. Warning: reed switches have a glass body which is easily broken!

Reed switches

Regulated power supply This is a typical simple regulator supply using an LM317Integrated circuit. Zener diodes can also be used to regulate low power to fixed levels.
Power suply schematic

Relays A relay is an electrically operated switch. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. The coil current can be on or off so relays have two switch positions and they are double throw (changeover) switches.
Relays allow one circuit to switch a second circuit which can be completely separate from the first. For example a low voltage battery circuit can use a relay to switch a 230V AC mains circuit. There is no electrical connection inside the relay between the two circuits; the link is magnetic and mechanical.
The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be as much as 100mA for relays designed to operate from lower voltages. Most ICs (chips) cannot provide this current and a transistor is usually used to amplify the small IC current to the larger value required for the relay coil. The maximum output current for the popular 555 timer IC is 200mA so these devices can supply relay coils directly without amplification.
Relays are usually SPDT or DPDT but they can have many more sets of switch contacts, for example relays with 4 sets of changeover contacts are readily available. For further information about switch contacts and the terms used to describe them please see the page on switches.
Most relays are designed for PCB mounting but you can solder wires directly to the pins providing you take care to avoid melting the plastic case of the relay.Relay schematicTypical relays Relay details

Resistor Resistor is the name for an electronic component exhibitingResistance. Resistance is the property of a component which restricts the flow of electric current. Energy is used up as the voltage across the component drives the current through it and this energy appears as heat in the component. Resistance is measured in ohms, the symbol for ohm is an omega. 1 is quite small for electronics so resistances are often given in k and M.1 k = 1000 1 M = 1000000. Resistors used in electronics can have resistances as low as 0.1 or as high as 10M.
Resistor network A set of resistors combined in one package for convenience in assembling circuits. Often abbreviated to "Resnet".

Examples of resnets

Resonator A device used to produce an oscillation of a specific frequency, primarily for use as the clock signal for digital circuits.
Reverse polarity The Positive voltage goes to the Negative part of a circuit and vice versa.
Used to reverse DC motors in trains.

Risk assessment An analysis of the risks and the method of management in a strategy or practice.
RMS This is what you read on an analogue meter used on AC voltage. It compares to the dc level. So it’s an average value.
Road Vehicle Control Usually refers to a electronic system to control model road vehicles.
Route setting This is used when you operate a set of instructions to drive a train from A >>>B with all the instructions to operate points and signals.
RPC Remote Panel Control RPC System - Remote Panel Interface (RPI)
(RS232 Single Unit PC Interface Module) Includes PCB and all components
a MERG system

RPI RPC System - RPI (Remote Panel Interface)
Serial interface module for PC control. RS485 Multi-Drop version. Includes PCB and all components. a MERG system

RS232 It is commonly used in computer serial ports. Is a standard for serial binary data signals connecting between a DTE (Data terminal equipment) and a DCE (Data Circuit-terminating Equipment) Wikipedia
RS485 It is commonly used in computer serial ports. RS485 enables the configuration of inexpensive local networks and multidrop communications links. It offers high data transmission speeds (35 Mbit/s up to 10 m and 100 kbit/s at 1200 m). Since it uses a differential balanced line over twisted pair (like EIA-422), it can span relatively large distances (up to 4000 feet or just over 1200 metres) Wikipedia
RSA The RSA is a RS 232 to RS485 converter a MERG system
RSE RPC System - RSE (Remote Stack Extension)
Allows a stack of RPC modules to be divided into remotely located parts, connected using standard 4 pair Cat 5 network cables. Includes PCBs and all components. a MERG system

RTC Computer controller train controller from the RPC collection a MERG system
SD4 RPC System - SD4 Accessory
(Multiple Aspect Signal Driver) Includes PCB and all components
a MERG system

Seep motor Proprietary brand of double solenoid motor for operating model points.

Seep point motor

Semaphore Railway signal giving indications to the train driver by means of the position of a mechanical arm.
Series A series circuit is when the items are in a line not like a ladder
Servo Servo motorGives a mechanical output for electrical input
Shift register Data received in the chip register is shifted right on the pulse received. One of the most common uses of a shift register is to convert between serial and parallel interfaces John Ferguson
Signalling Could be any form of indication to an model railway operator
Smoothing The addition of components to a power supply to reduce peaks in the flow of current . John Ferguson
Solid conductor Category 5e and Category 6 network cable comes in a solid conductor format, and in stranded conductor formats. People often ask which is appropriate for their application. We'll detail the difference between two types of cable, and help you decide which application is suits which cable.
Solid conductor uses 1 solid wire per conductor, so in a standard Cat 5e / Cat 6 4 pair (8 conductors) roll, there would be a total of 8 solid wires. Stranded conductor uses multiple wires wrapped around each other in each conductor, so in a 4 pair (8 conductors) 7 strand roll (typical configuration), there would be a total of 56 wires.
Solid conductor cable is most useful for structured wiring within a building. It is easily punched down onto wall jacks and patch panels since it is a single conductor. The wire seats properly into insulation displacement connector. Solid is less useful when you are terminating with standard RJ45 connectors, as used when making patch cables. Most RJ45 connectors use 2 prongs which penetrate the conductor itself. This is not desirable, since solid cable has the tendency to break when penetrated by the prong. Using a 3 prong style RJ45 connectors creates a much better connection as it doesn't break the conductor - the 3 prongs style connection wraps around the conductor instead of penetrating it. All being said, it is recommended that stranded network cable be used for patch cables - they make better quality RJ45 termination connections than even using 3 prong connectors.
Stranded cable is much less useful for punching down on wall jacks because the strands do not keep their perfect round shape when thrust into an insulation displacement connector. For best results, use solid for wall jacks and stranded for crimp connectors. Stranded cable is typically used to create patch cables. The cable itself is more flexible, and rolls up well. The RJ45 terminators have a better, and more flexible and complete connection to stranded wires than solid wire

Sound decoder This is a type of DCC digital decoder fitted in locomotives to provide appropriate simulated sounds in time with its operation. It can also include motor control or can be an addition to a decoder dedicated to control of the motor. A speaker is attached to reproduce the sound. Some makes can be programmed to receive sound files. John Ferguson
Soundtrax An American manufacturer of DCC sound decoders John Ferguson
SPDT This is the description of the electrical contacts in a switch or relay:
SP: Single Pole (one wire will be switched)
DT: Double Throw (1 contact may be connected to either of two others)

Sprog SPROG is a computer based programmer for DCC decoders.

Links:
http://www.sprog-dcc.co.uk

SPST This is the description of the electrical contacts in a switch or relay:
SP: Single Pole (one wire will be switched)
ST: Single Throw (off or 1 contact)

Updated: Jul-2006
SRI4 Part of the RPC series of products offered by MERG member Gordon Hopkins.
SRI4 provides for the RPC system to read up to 4 Bytes (=32 bits) of logic data for transmission to the remote panel or computer.
See TBs in the G16 series

Updated: Jul-2006
SRO4 Part of the RPC series of products offered by MERG member Gordon Hopkins.
SRO4 provides for the RPC system to write up to 4 Bytes (=32 bits) of relay drive data for transmission to the layout from the remote panel or computer.
See TBs in the G16 series

Updated: Jul-2006
SSI SSI is a Model Railway Control System family of software products offered byGramam Plowman in Australia...see the website
'Highly reallistic Looks and operates like real IECC (Integrated Electronic Control Centre) systems commonly used across the UK and the World. Full control of turnouts and signalling. Full interlocking support which is highly configurable. Fully implements Entry/Exit (NX) functionality. Simplifies and reduces the cost of your layout wiring. Simple and Easy control of your layout! '

Links:
http://www.gppsoftware.com

Updated: Jul-2006
Star network Star Network is a generic term that describes any network that is configured like the rays of light that radiate from a star, that is, there is a centre point and all other points radiate out from the centre.
A Star Network is often recomended for use in the ground system of sensitive equipment, where each separate element is separately connected to the central ground point or 'Star Point', this is done so that individual ground currents do not flow in common wires and thus interfere with each other, probably causing crosstalk which can spoil an HiFi installation with 'Hum' or can cause unreliable operation in a digital system.

Updated: Jul-2006
Stationary decoder For MERG this usually refers to a DCC decoder that is not intended to be mounted in rolling stock.
For example it may be intended for controlling track-side equipment, such as switch machines, signals, uncouplers, lights, level crossings, sound devices etc.

Updated: Jul-2006
Steady state Apart from Fred Hoyle's theory of the 'Steady State Universe' in which the density remains constant with time, although the Universe is expanding, in electronics we have a simpler viewpoint:
When a process starts, it may cause surges of the working fluids (eg water/steam/electricity) after the initial acceleration the process may be assumed to continue at constant level, or to have reached 'Steady State'.
A good example is a car starting from cold and accelerating from rest to a cruising speed...during acceleration fuel consumption is high, but this settles to steady state conditions in the cruise and as the entire machine warms up.
For MERG one explanation for 'Steady State Decoder' is to distinguishit from 'Pulsed Decoder'. The pulsed decoder is usually related to solenoid switch machine, which requires a capacitor discharge device to provide high transient power (maybe 5Amps for 20mS). In contrast the steady state decoder is intended for non pulsed functions, such as micromotor operated machines, and can have a lower cost design.

Updated: Jul-2006
Stranded conductor Stranded wire is composed of a bundle of small-gauge wires wrapped in a single piece of insulation to make a larger conductor. Stranded wire is more flexible than a single, thick strand of the same gauge, or crossectional area.
Another form of Stranded Wire is called "Litz wire" which is used in coils that are used as inductors in high-frequency tuned circuits, because at high frequencies electricity travels near the outside of the wire. This is called the skin effect.

Updated: Jul-2006
Super Bloc This is the Name for a set of ideas and kits started by MERG member JJ Matthews and his team which provides for automation of the principle of block control, observing signal logic and providing smooth accelerations, if required without human intervention.
The TB-33 series describes and Kit #38 to 40 provides the hardware.

Updated: Jul-2006
Surface Mounted Components In the context ofMERG this refers to electronic components that are intended to be mounted directly by being soldered onto the conducting tracks on the surface of a printed circuit board (PCB), usually without drilling any holes. The opposite is 'Through Hole Mounted' in which all the connections pass through the PCB to be soldered on the side opposite to the component.
Working with Surface Mount Devices is discussed in one of the Babani books.

Updated: Jul-2006
SWG Standard Wire Gauge, this is the Imperial standard for wire gauges, the reference shows a table of sizes for this series and the American similar (but different) table 'AWG'.
Updated: Jul-2006
Switch A 'Switch' can have2 prime engineering meanings:
The simplest is an electrical switch, as in 'Light Switch' which is amechanically operated device used for connecting or disconnecting electrical circuits. Such switches can have many contacts and become quite complex.
The second meaning is the American term for the English 'Points'...this being the scheme to allow a railway track to diverge or converge with another route. It allows the path of the train to be 'switched' from one route to another.

Updated: Jul-2006
Switch machine In model railways, as on the real railway it is now usual to operate 'switches' (points) using a small electrical machine, called the 'Switch Machine', or in UK probably point motor. Switch machine exist in many forms, each with its protagonists:
Solenoid operation: tend to be very violent and require special arrangements for driving reliably (eg Capacitor Discharge)
Slow Motion: usually small DC motor operated.
See MERG newsletter Spring 2005, page 12

Updated: Jul-2006
Switch mode A switched-mode power supply, switching-mode power supply or SMPS, is an electronic power supply unit (PSU) that incorporates a switching regulator. While a linear regulator maintains the desired output voltage by dissipating excess power in a "pass" power transistor, the SMPS rapidly switches a power transistor between saturation (full on) and cutoff (completely off) with a variable duty cycle whose average is the desired output voltage.

Advantages include smaller size and lighter weight (from the elimination of low frequency transformers which have a high weight) and lower heat generation from the higher efficiency. Disadvantages include greater complexity, the generation of high amplitude, high frequency energy that the low-pass filter must block to avoid electromagnetic interference and a ripple voltage at the switching frequency and the harmonic frequencies thereof
Wikipedia
Tag strip Point-to-point construction uses terminal strips (also called 'tag boards' of 'tag strips'). A terminal strip is a stamped strip of tin-plated loops of copper. It is mounted in a way that electrically insulates it. The metal loops are mounted on a cheap, heat-resistant material, usually synthetic-resin bonded paper (FR-2), or bakelite reinforced with cotton, or sometimes paxolin. The insulator has an integral mounting bracket, sometimes shorted to the stamped loops to ground them to the chassis.
Tag boards are usually in the form of two rows of tags mounted at each edge of the insulating board to allow axial components to be mounted between them, and wires to be easily attached. Before 1960 or so most electronic equipment was wired with this type of assembly.
Tag Strip is usually a single row of solder tags mounted on a narrow insulating strip, designed with mounting feet so that it stands a right angles from the base(board). These are commonly used in model railway layouts to keep cabling tidy and neatly terminated.

Updated: Jul-2006
TB Technical Bulletin,an entire catalog of MERG publications,having the objective to disseminate techincal information to the membership. Access is through the 'members only' section of the website:
Updated: Jul-2006
TCC This is a Java Script control interpreter written by MERG member Howard Amos which provides an easy interface to Gordon Hopkins RPC range of modules using an RS232 interface from a PC (or MAC) allowing the logical control of all the modules functions, whether feedback (like ToTI) or control (eg relays, logic, relay switches, point motors, etc.)
This capable program is described and can be downloaded from the MERG website:

Links:
/merg_resources/tcc.php

Updated: Jul-2006
Technical Data This is a generic term used in Electronics to describe 'data sheets' for electronic parts or components, or to describe the engineering oriented detailed description of a product. It may include absolute maximum limiting factors, typical performance, operating limits, power consumption etc.
Technical Data for a real steam locomotive might include working boiler pressure, weights, tractive effort, specific coal consumption, physical dimensions etc.

Updated: Jul-2006
Throttle/handset The Throttle controls the power output of an internal combustion engine, in model railways it represents the, usually electrical, controller that is used to adjust the speed of the train being driven.
The physical form of the 'throttle' can be a knob or buttons mounted directly on the model railway controller, or they may be mounted independently in a small box, usually called a Handset, which is attached to the main controller by a thin wire, radio link or infra red link.

Updated: Jul-2006
Timers The basic timer is the Kitchen Timer, consisting of some sort of clock and alarm that can be set as required.
In electronics timers exist in various forms and may be intended for setting a time or delay, for measuring a time or time interval. They can be implemented digitally typically by counting a 'clock' or oscillator (as in a PIC implementation) or using an analog timer, such as the well known '555' timer device.

Updated: Jul-2006
Toggle A 'Toggle' is a combination of an operating lever and spring loading which causes the lever to be 'locked' at one or other extreme position. It is extensively used in mechanical assemblies, in which the extremes may be 'locked' by the 'toggle spring'. Another example is the 'Mole' self locking wrench in which the toggle action also gives strong mechanical advantage.
The Electronic version is also a device that can be 'latched in one position or another, indeed sometimes called a 'latch'.

Updated: Jul-2006
Tortoise motor The commercial name given to a model of turnout actuator or motor manufactured by Circuitron in the USA. This device features a high torque low-speed motor which is geared down to provide the drive to move the throwbars of model railway turnouts. A MERG Technical Bulletin A6/3 shows the data sheet for this device
Updated: Jul-2006
Toti Train-on-Track Indicator. A device or electronic circuit designed to interwork with, or form part of a track circuit which provides an output suitable for connecting to signalling, an indicator panel or other electronic component such as a computer, when a piece of track or block section is occupied by a train or item of rolling stock. There are a number of MERG designs featuring amongst the Technical Bulletins, three of which have been offered as kits. See kits nos.56 (DCC only), 62/63 (DC and DCC) and the RPC FTC module.
Updated: Jul-2006
Track circuit A method of isolating a section of track so that an electric current flows when that section is occupied by a train or item of rolling stock. MERG Technical Bulletin T9/1 deals with 2-rail track circuits
Updated: Jul-2006
Track cleaner A device for cleaning track so that dirt or other deposits do not impede the flow of electric current. A number of methods exist to accomplish this. MERG Technical Bulletin A4/1 features the Relco Track Cleaner which superimposes a high frequency, high voltage signal over the traction current. This burns through track deposits when traction is interrupted. Mechanical abrasive rubber-type products are also available such as the Peco PL41 Rail Cleaner and the MERG kit 83, PCB and Track Cleaner. These must be rubbed over the track to clean it. A variety of solvents applied with a clean cloth are also suitable as are a number of wagon-mounted abrasive blocks. A popular MERG method is to polish the rail tops with the rough surface of common hardboard.
Updated: Jul-2006
Train detection A means of generating a signal when a train or item of rolling stock is present. Quite commonly accomplished by means of a track circuit and ToTI, FTC or DTC module which detects an object for the whole of its traverse through a track section but also possible using spot detectors such as infra-red devices (see MERG Hector kit 72), Hall effect switches (see MERG kits 101, 102 and 103) and magnetically-operated reed switches (see MERG kits 97 and 104 - 109)
Updated: Jul-2006
Transducer A collective term used to describe devices that convert one form of energy into another, generally for the purpose of detection, measurement, actuation or information transfer. Most often of electrical or electronic nature, the most common forms of transducer are either sensors or actuators and thus find common usage in model railway systems. Such examples can be found in a number of MERG kits for train detection and turnout actuation and are either the device that physically detects the presence of rolling stock such as a Hall effect switch or infrared sensor or the coil that drives a turnout throwbar.
Updated: Jul-2006
Transformer A electrical device consisting of two or more coils of insulated wire wound round an iron core to allow a focussed and fluctuating magnetic field generated by the alternating current in one coil to induce an alternating current in the other coil(s). Most frequently used to change the voltage of a power distribution or electronic signal from a high value to a lower value or vice versa. Commonly found in the mains power distribution network between power station and consumer and usually found in the power supplies of most appliances used in the home.
Updated: Jul-2006
Transistor A triple-layered semiconductor assembly made from doped silicon or germanium arranged so that potential differences between the layers allow this device to be used as an amplifier, switch, voltage stabiliser, signal modulator and many other uses. Positive-doped layers are termed P and negative-doped layers are termed N so that transistors can be NPN or PNP, operation of one being the inverse of the other. Control is achieved by allowing a small current to flow into the centre layer, called the Base, and this invokes a larger current to flow between the outer layers, the Emitter and the Collector. Transistors feature either as individual components or packed in many thousands into Integrated Circuits and form the basis of modern electronic technology. First patents were filed for a transistor as early as 1928 and again in 1934 but the first successful device is believed to have been constructed by Bell Labs in 1947.

Transistor symbols

The leads are labelled base (B), collector (C) and emitter (E).
These terms refer to the internal operation of a transistor but they are not much help in understanding how a transistor is used, so just treat them as labels!

Updated: Jul-2006
Turnout actuator A collective term that refers to the device that switches turnouts by means of a mechanical linkage, so that trains can be diverted from one track to another. A common example is the twin solenoid arrangement that, when pulsed with an electric current, cause the turnout throwbar to switch from one side of the track to the other. Actuators can also consist of high torque motors or servos that change the turnout direction in response to an applied control signal.
Updated: Jul-2006
Twinkling The description given to the fast, frequent and random change of brightness of a light source. The most common example is to be found in the appearance of stars in the night-time sky which twinkle in response to random fluctuations of water vapour density in the Earth's atmosphere affecting the path of the stars' light. A MERG kit is available (kit 61, Gas Lamp Twinkler) which applies random variations of current to a connected LED thus simulating a twinkling gas lamp.
Updated: Jul-2006
Unregulated power supply A Power Supply Unit (PSU) in which there is no controlled stabilisation of the voltage output applied electronically. The voltage supplied by a loaded PSU is therefore lower than one which has no load connected due to the increase in output current having a variety of effects, principally through impedance or resistance in the PSU components.
Updated: Jul-2006
USB The shorthand term used to denote a standard Universal Serial Bus developed to allow the interconnection of many peripheral devices such as mice, keyboards, joysticks, scanners etc., to a computer such as IBM compatible and Apple PCs. Developed by collaboration amongst leading companies in the computer and electronics industry, the specifications are standardised by the USB Implementers Forum (USB-IF). USB 3 has recently become more readily available and offers speeds up to 5Gbps.

Links:
http://www.usb.org

Updated: Jul-2010
Volt A unit of electromotive force defined as the potential difference across a conductor when a current of 1 ampere dissipates 1 watt of power. Used as the universal measure of electrical 'force' across the World, it was named in honour of the Italian physicist Allessandro Volta who invented the first chemical battery. Its precise value was fixed by the 18th General Conference on Weights and Measures in 1948 and is maintained internationally for practical measurement by the US National Institute of Standards and Technology (NIST) through the development of the Josephson junction array chip.

Links:
http://www.nist.gov

Updated: Jul-2006
Voltage regulator An electronic circuit composed of discrete components or packaged in an Integrated Circuit, which is designed to render the output voltage of a PSU or other device, constant irrespective of load applied. A simple semiconductor example is a zener diode but many more complex designs are now available at a range of output values and powers such as those incorporated into the 7800 and 7900 series IC regulators.
Updated: Jul-2006
Watt A unit of power most often used in the electrical and electronic industries and is defined as one joule of energy per second. Named after the British Engineer James Watt, it was adopted by the Second Congress of the British Association for the Advancement of Science in 1889. All household appliances have the amount of power in watts that they consume imprinted somewhere on the casing. Watts in the electronic arena are calculated as volts x amperes.
Updated: Jul-2006
Welding simulator An electronic circuit that creates short intensity high brightness sparking or flashing to mimic that caused by the process of welding. The MERG kit 61 Gas Lamp Twinkler can be modified to produce this effect with the use of suitable high brightness LEDs
Updated: Jul-2006
Zener diode A type of diode named after the American physicist Clarence Melvin Zener who discovered a method of creating controlled breakdown at a specific voltage in a specially doped P-N semiconductor junction. When reversed biased, the zener diode behaves like a conventional diode and passes little or no current until the reverse voltage reaches the breakdown voltage when current will begin to flow. At this point the reverse voltage is maintained more or less constant irrespective of increase in current so that the zener diode can be used as a reference or stabilising component for voltage regulation. Zener diodes are available at a range of breakdown voltages which are quite accurately defined by the doping process in the manufacturing stage. See the BZX84 (0.3w), BZX55 (0.5w) and BZX85 (1.3w) series of diodes.
Updated: Jul-2006
Zero 1 An early form of Command Control for model railways, Zero 1 was launched in 1979 and systems incorporating the technique were marketed by Hornby and Hammand and Morgan. Now obsolete, having been overtaken by the DCC system, Zero 1 pioneered the concept of controlling model railway motors by establishing a constant track power source that included control signals to define locomotive identity, speed and direction. The MERG series of Technical Bulletins CC1 written when Zero 1 was popular, remain an important source of information and techniques on this system. A MERG kit 71 is still offered which provides replacement parts for Zero 1 system keyboards. Some of the DCC decoders supplied by ZTC Controls Ltd. can also be used with the Zero 1 system.
Updated: Jul-2006
ZIMO ZIMO ELEKTRONIK, an Austrian company based in Vienna, first launched a digital model railway control system in 1979 and progressively developed the system through the 1980s and early 1990s to include decoder BEMF, block control, route setting and a push button CTC panel amongst other advanced functions. Switching to the emerging DCC standard in 1996, ZIMO swiftly gained a reputation as the 'Cadillac' of DCC suppliers and maintains a leading industry position at the time of writing.

Links:
http://www.zimo.at/web2007/index2E.htm

Updated: Jul-2006
ZTC ZTC Controls Ltd, a British supplier and designer of DCC systems now based in Yeovil after the former manufacturer ceased trading. ZTC has over 25 years of design and manufacturing experience and has supplied DCC systems for Network Rail training schools.

Links:
http://www.ztccontrols.co.uk/site/

Updated: Jul-2010