Glossary of Electronic Terms Used in the MERG Journals and Technical Bulletins

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Updated 7 June 2008.

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Subject	Explanation	Source/Contributor
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 2006
Baud	http://www.cnet.com/Resources/Info/Glossary/Terms/baud.html Most people use baud to describe modem speeds in bits per second--but they're 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 aren't 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.	AJC 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 <http://www.merg.info/Members/tb.htm#T> - The BC3 kit is No38 Nos 39 and 40 are a test jig and a setting up kit <http://www.merg.info/Members/kits.htm>.  Kit instructions for 38 and 39 are available from <http://www.merg.info/Members/kits/kitinstructions.htm>	AJC 2006
Bell signals	Bell Signals were used to convey information from between signal boxes <http://www.signalbox.org/block/bells.shtml>	AJC 2006
Bipolar	?Bipolar transistor - presumably not bipolar disorder or manic depression.	AJC 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 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.   <http://www.signalbox.org/block.shtml 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.	AJC 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 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.  <http://www.merg.org.uk/resources/blong/superbloc2.html> 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. <http://ngaugesociety.com/benefits/areagrp.php3>	AJC 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.  <http://www.ithaca.edu/library/course/expert.html There is nowhere in Boolean for MAYBE or DON'T  KNOW.	AJC 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 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 06_2006 /John Ferguson
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.   The diagram shows the operation of a bridge rectifier as it converts AC to DC. Notice how alternate pairs of diodes conduct.	Wikepedia 06_2006 /John Ferguson
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 06_2006 /John Ferguson
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 06_2006 /John Ferguson

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Subject	Explanation	Source/Contributor
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. 06_06 /John Ferguson
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 06_2006
Cabling	Refer to 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 06_2006 /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 06_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 06_2006 /John Ferguson
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 06_2006 & MERG Secretary John Ferguson 06_2006 /John Ferguson
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 03_2006 /John Ferguson
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 03_2006 /John Ferguson
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 06_2006 /John Ferguson
Cleaning Tracks	There is a commercial product called Relco. More information on cleaning tracks can be obtained from Southern E-Group web site http://freespace.virgin.net/c.gardner/semg/relco.htm	MERG Secretary John Ferguson 06_2006 /John Ferguson
Clearing point	This is a location in advance of a signal box up to  which the track must be clear to 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 03_06 /John Ferguson
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 06_2006 /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 06_2006 /John Ferguson
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 06_2006 /John Ferguson
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 06_2006 /John Ferguson
Colour light	Refers in model railways to model signals with coloured LED lights for red, amber, and green.	MERG Secretary John Ferguson 06_2006 /John Ferguson
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 06_2006 /John Ferguson
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	See http://rail.felgall.com/crw.htm for more details.
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.
CV's	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.

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Subject	Explanation	Source/Contributor
Electro frog	Is a Peco term for live(power) frogTurnout(Switch or Points),what some people call power-routing. http://www.loystoys.com/peco/about-electrofrog.html	PECO 07_2006
Electro magnet	Is a coil of wire in air or on a former that if current is passed through the wire a magnetic field will be prduced http://www.le.ac.uk/se/centres/sci/selfstudy/mam11.htm	MERG Member BRIAN JOHNSON 07_2006

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Subject	Explanation	Source/Contributor
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 07_2006
Handset	Is a means of control in your hand.	MERG Member BRIAN JOHNSON 07_2006
Header plug or  socket	Are plug&sockets primarily for use on PCB boards to make connections to and from the board	MERG Member BRIAN JOHNSON 06_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.   http://www.kpsec.freeuk.com/components/heatsink.htm	kpsec 06_06
Hector	This is a track detector using an optical system to detect the location of train    Merg kit  for members	MERG Member Bryan Knight 07_06
High	This what we call greater than the base voltage or ground e.g. so high is 5v ~ 4.4volts above 0	BJ 2007
HYPOTRAC	This a high voltage track detector system for 2 rail Model railway track , see TB T9/2 merg members only	Merg John Dowm TB 07_2006
Hysteresis loop	Hysteresis is well known 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. http://en.wikipedia.org/wiki/Hysteresis	Wikepedia 07_2006

Subject	Explanation	Source/Contributor
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. http://www.kpsec.freeuk.com/components/ic.htm	kpsec 07_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. http://www.kpsec.freeuk.com/components/lamp.htm	kpsec 06_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 Are sometimes called chokes) They pass DC easily, but block AC signals ,This is the opposite to capacitors, http://www.kpsec.freeuk.com/components/other.htm/inductor	kpsec 06_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	MERG Member BRIAN JOHNSON 06_2006
Infra red receiver/detector	Two types of IR receivers are used, a phototransistor or a photodiode	MERG Member BRIAN JOHNSON 06_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 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 2006

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Subject	Explanation	Source/Contributor
Latching	A pulse method to change the state from on to off or vice versa, see: http://www.heathcote-electronics.co.uk/RelayBrd.htm http://www.4qdtec.com/trd.html	BJ 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 2007
LED	Light Emitting Diodes (LEDs) emit light when an electric current passes through them, see:    http://www.merg.org.uk/led/index.htm or http://www.kpsec.freeuk.com             Example:       Circuit symbol:	BJ 2007
LENZ	A German dcc system and decoder manufacturer	BJ 2007
Lighting decoder	A DCC decoder made especially for lights for a loco or carriages, see:   http://www.electricnose.co.uk/dcc/dccbachmann158.html http://www.btinternet.com/~modern.image/Voyagerlights.htm	BJ 2007
Logic	http://en.wikipedia.org/wiki/Logic In a model railway it is a way to do step by step sequence to make the train do what you require.	BJ 2007

Subject	Explanation	Source/Contributor
Negative	A DC term that means the voltage is lower than 0 You can have it plus or minus the zero point	BJ 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 2007
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"
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. Input A 0 0 1 1 Input B 0 1 0 1 Output Q 1 0 0 0 Traditional symbol IEC symbol Truth Table

Subject	Explanation	Source/Contributor
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 compter 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

Subject	Explanation	Source/Contributor
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! Photograph © Rapid Electronics
Regulated power supply	This is a typical simple regulator supply using an LM317 Integrated circuit. Zener diodes can also be used to regulate low power to fixed levels.
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.
Resistor	Resistor is the name for an electronic component exhibiting Resistance 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".
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

Subject	Explanation	Source/Contributor
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.
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	Gives 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	http://www.sprog-dcc.co.uk/ SPROG is a computer based programmer for DCC decoders.
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)	July 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	July 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	July 2006
SSI	SSI is a Model Railway Control System family of software products offered by Gramam 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! ' http://sitenet.gppsoftware.com	July 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.	July 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.	July 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 distinguish it 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.	July 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.	July 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.	July 2006
Surface Mounted Components	In the context of MERG 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.	July 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' http://www.comax.uk.com/wire_gauge_chart.htm http://home.datacomm.ch/hb9abx/wire_gauge.htm	July 2006
Switch	A 'Switch' can have 2 prime engineering meanings: The simplest is an electrical switch, as in 'Light Switch' which is a mechanically 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.	July 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	July 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