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Glossary of terms you will come across during your Phase 2 training.


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 Two possible meanings here: it can either mean 'integrated circuit' (for example, the 555 chip) or collector current, refers to the amount of electricity flowing in the collector/emitter (c/e) circuit of a transistor. Different transistors have different tolerances, and you should consult the relevant datasheet to find the recommended collector current for a particular transistor.

Transistor data

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Idle circuitWhen an engine is idling, it is ticking over, running slowly and doing no useful work. The throttle flap is almost fully closed, which means that vacuum being generated by the downward movement of the piston(s) cannot act on the main jet, to draw in fuel. As a result, the engine runs slowly.

In order to keep the engine ticking over, it needs fuel, so we use the idle circuit, which has a small drilling just below the throttle flap. This ensures the engine can still draw fuel, even though the throttle flap is almost entirely closed.

As we open the throttle flap, vacuum is allowed to act on the main jet, drawing more fuel. Due to the inertia of the fuel, it will take a little time for the carburettor to respond to this changed throttle setting, so sometimes, progression jets are used as the transition is made from almost closed throttle (engine ticking over), to fully open throttle (engine at maximum power and drawing off the main jet).

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This is the speed an engine is set to run to when it is idle - when there is no working load on the engine.

It is commonly referred to as 'tick-over' speed.

In larger petrol and diesel engines, the idle speed is set by the ECU.

In smaller petrol and diesel engines (of the type used in small plant machinery), the idle speed is set at the carburetor (petrol enignes) or the fuel injection pump (diesel engines).

Setting the idle speed is often crucial for the satisfactory operation of the engine. For example, in a consaw, the idle speed must be set so that the no drive is taken up, and the cutting disk does not spin when the engine is idling.

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In a four stroke engine, a stroke is an upward or downward movement of the piston. Each stroke is half a revolution of the engine. There are 4 strokes:

  1. Induction
  2. Compression
  3. Power
  4. Exhaust

Of the four strokes, only one, the power stroke, produces power. The other 3 strokes are used to make the engine function. Because they do not directly produce power, the induction, compression and exhaust strokes are known as idle strokes.

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International Standards and conformity assessment for government, business and society for all electrical, electronic and related technologies.

Check here for more information.

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Abbreviation for 'ignition switch'. This is a legend that may be added to wiring diagrams to let you know that a particular circuit is controlled by the ignition switch - it is said to be 'live under key', or only live when the ignition is switched on.

In diagrams that use DIN numerical codes, terminal 30 is battery +, and terminal 15 is an (ignition) switched live. In other words, something marked '30' is live all the time, whereas something marked '15' is only live when the ignition is switched on. In this system, terminal '1' is ground.

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In electronic ignition systems for petrol engines, the ignition driver stage controls the flow of primary current in the coil. To do this, it acts on signals from the distributor: a square wave in the case of Hall effect type distributors, and a sine wave in the case of inductive systems.
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An ignition turret.A complete ignition system, mounted on a stand-alone unit, allowing for the in-depth study of that system. It is completely self-contained, with 4 spark plugs, HT leads, motor drive, vacuum advance and ignition timing indicator. The unit is provided by AG Block, and is designed for use with the Wilkinson electrical trainer.
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The Institute of the Motor Industry: A UK based professional association for people involved in the motor trade and the automotive industry in general. Membership is open to all involved in the trade, technicians or managers.
The Irish branch of the IMI run seminars and lectures from time to time. These are generally notified on the C.P. Fitters online learning environment site news. Anyone subscribed to this forum will receive these notices.

Apprentices should note that student membership is available at a reduced fee.

More on the IMI

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Impedance is the opposition that a circuit presents to the flow of electrical current.

In circuits carrying steady direct currrent, the impedance of the circuit is simply the resistance of that circuit.

In circuits where the current varies or alternates, the impedance of that circuit is the resistance plus the reactance of the circuit.

Note: Most of the time, in automotive D.C. circuits, the flow is referred to as "steady flow". However, D.C. will depart from or approach steady flow, particulary when switches are opened and closed.


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