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


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Picture of Lorcan McGivney

Lorcan McGivney

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A bridge wave rectifier utilises at least four diodes to control the flow of the current produced by the geneator. If we look at the wiring diagram for a simple bridge wave rectifier we can see that the input is coming in between two sets of diode pairs with anode to cathode configuration. this ensures that regardless of the direction of flow from the alternating input whether its negative or positive, the incoming current can only flow in one direction.

Bridge wave rectifier and rectification


Contributor: Lorcan McGivney, CP Fitters, January to May, 2012.

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Picture of Matt Molloy

Matt Molloy

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A science Master's Degree.
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Technicians who succesfully complete their National Craft Certificate (formerly the Senior Trade Certificate) and the Advanced Automotive Technological Certificate are awarded a Technicians Diploma and are entitled to use the title Tech. Dip.
Picture of Padraic Kelly

Padraic Kelly

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Coolant is the liquid that absorbs heat from the engine and then dissipates it through the radiator. It can also dissipated through the cab heater in the drivning compartment of the vehicle.

The main component of coolant is water, for the following reasons:

Pure water as coolant does have the following disadvantages:

  • Water boils at 100oC, and turns to steam.
  • Water freezes at 0oC, crystallises and expands. This will cause it to damage whatever system it is enclosed in.
  • Water causes corrosion.

Water as coolant does have big advantages, that is why we use it, but we must add things to it, and do things to the environment in which we store and work it:

  • Water boils at 100oC and turns to steam. This temperature is below what many modern engines want to operate at. In order to raise the boiling point of the water, we pressurise the cooling system.
  • If we allow the water to freeze, it will crystallise and turn to solid ice. When it does this, it will expand and crack the system in which it is contained. In the case of the cooling system, this means the engine block and hoses can get damaged.
    To avoid this, we add anti-freeze to the water.
  • Water causes corrosion, so we must add some sort of inhibitors such as rust inhibitors.
  • Water causes scale - just look at the element in an old electric kettle. To avoid scale build up inside the water passages of the engine, we add inhibitors. Scale build up will restrict proper coolant flow and slow down heat transfer.
  • Whilst pure water is a poor conductor of electricity, the water found in cooling systems is not pure, and it will conduct electricity. A liquid that conducts electricity is known as an elecrolyte.
    In addition, inside a cooling system, there are many different types of metals.
    This makes a liquid cooled engine one big battery: dissimilar metals immersed in an electrolyte. Because of this, coolant must contain some sort of electrolytic inhibitor.

Checking Coolant

All modern cooling systems are sealed and as a result they shouldn’t ever really need topping up between car services provided everything in your vehicle’s engine is functioning correctly. It is a pressurised system and as such should only be checked or topped up when the vehicle's engine is cold.

Benefits of coolant:

  • No corrosion - By replacing corrosive water with engine coolant solution, you will prevent corrosion damage.
  • No scale - Complete elimination of scale build up inside the water passages of the engine. In addition, "hard" fresh-water causes scale form, and this will restrict proper coolant flow and heat transfer.
  • No electrolysis in the engine.
  • Anti-freeze protection.


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Picture of Simon  Bramble

Simon Bramble

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generator with earth leakage circuit breakerThe Earth Leakage Circuit Breaker is a safety device used in electrical installations with high earth impedance to prevent shock. It detects small stray voltages on the metal enclosures of electrical equipment, and interrupts the circuit if a dangerous voltage is detected.

Basically what it does is if the ELCB detects a voltage leak,it will open the circuit, stopping the machine from operating.

You can read more about ELCBs on Wikipedia

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Site Administrator

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> means greater than -example 2 > 1

< means less than - example 1 < 2

≤ means less than or equal to.

≥ means greater than or equal to.

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Lambda, a letter from the Greek alpahbet. In automotive engineering, it is used to represent the stoichiometric ratio of the amount of air required to burn a fuel. For example, for diesel, the value is approximately 14.5:1, meaning that it takes 14.5 parts of air to burn 1 part of diesel.

The stoichiometric ratio for petrol is approximately 14.7:1.

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Pi, Greek letter used to represent how many times the diameter of a given circle will fit into its circumference. This is constant at 3.142. Apprentice cp fitters use this figure for many calculations, for example: when calculating the capacity of an engine; when calculating centrifugal force and when calculating the peripheral speed of a cutting disk.
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1104D Perkins common rail engineThis is a Perkins designation, and refers to the 1100 series engine. The '4' refers to a four cylinder engine, and the 'D' refers to the common rail engine.

This engine has full electronic control of the fuel system - common rail with electronic injectors. 

As of April, 2012, we operate 3 of these engines.

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The 1106C Perkins diesel engineThis designation refers to the 1100 series Perkins engine. The '6' refers to the number of cylinders, and the 'C' refers to the fuel injection system, which is mechanical, based around a rotary fuel injection pump. This engine is the forerunner of the 1100D common-rail engine. Currently, the section is equipped with 6 1106C engines and 3 1104D engines.

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Typical 12V electrical training boardDuring the electrical module, one of the suggested exercises is to construct various electrical circuits such as parking lamps, headlamps (including relays) and glow plug circuits (including solenoid control).

In order to facilitate this exercise, we use 12V electrical training boards. These are boards of steel construction, with a working tray and a base that can accommodate a 12V battery.

This set up allows apprentices to construct the various circuits, and connect the board to an engine fitted with an alternator.

This set up allows each apprentice to wire up all the basic electrical circuits and components found in a typical plant vehicle.

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Typical 12 volt electrical test lampThis consists of a 12V lamp, with two different terminals. One terminal (the earth terminal) consists of a short cable and a crocodile clip. The other terminal is at the pointed end of the tool. It is used by fastening the crocodile clip to a good earth point, and then using the sharp end of the took to probe wires. If the wires are live, the lamp will glow.

During the induction phase of the course, you will be issued (at your own expense) with a 12V test lamp.

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Typical diodeOne of a series of diodes (the 1N4000 series). They are popular, 1 amp, general purpose, silicon rectifier diodes.

During the Phase 2 course, we use these diodes to make half-wave rectifiers, full-wave rectifiers, and to suppress voltage spiking on 30 amp relays in circuits such as the time-delay circuit built as part of the Electrical Module.

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Crowsfoot injector removal toolCrow's foot tool that allows you to tighten injector pipe unions with a 3/8" torque wrench.
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The 3 effects of electicity.

3 Effects of electricity:

  1. Chemical change  - For example, the electrolyte in a battery changes from sulphuric acid (H2SO4) when the battery is charged, to water, H2O, when the battery is discharged.
  2. Heat - For example, current passed through a bulb causes the filament to glow white hot. This is incandescent heat.
  3. Magnetism - for example, when we pass electrical current through the commutator and the field windings of a motor, like poles come into close proximity. These poles repel each other, giving us the motoring action.
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DIN numerical wiring code:

  • 15: Battery live supply controlled by the ignition switch (often referred to as 'live under key').
  • 30: Battery live or battery positive (+)
  • 31: Battery earth or Ground (-)

Other codes you will come across on Phase 2 training include:

  • 85: End of coil (for example, the end of the coil windings on an electromagnetic relay)
  • 86: Start of coil (for example, the start of the coil windings on an electromagnetic relay)
  • 87: To load (for example, on an electromagnetic relay, battery positive is supplied to terminal 30 on the relay. That leads to a set of contact points, and the far side of those contacts is terminal 87, which leads to whatever load the relay is serving.

Understanding European DIN Codes (PDF document download)

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Injector clamping boltInjector clamp bolt.
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Also written as 50 Hz or 50Hz.

This is the frequency at which mains electricity in Ireland is delivered at.

We know that in an AC circuit, rather than flow constantly in one direction, the electrons move rapidly back and forth. The rate at which these electrons move back and forth is referred to as the frequency of the supply. In Ireland, the mains AC supply has a frequency of 50 Hz. In other words, the electrons in our homes move back and forth in the wires 50 times every second when a circuit is closed.

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From Wikipedia:

555 chipThe 555 Timer IC is an integrated circuit (chip) implementing a variety of timer and multivibrator applications. The IC was designed by Hans R. Camenzind in 1970 and brought to market in 1971 by Signetics (later acquired by Philips). The original name was the SE555 (metal can)/NE555 (plastic DIP) and the part was described as "The IC Time Machine". It has been claimed that the 555 gets its name from the three 5-kohm resistors used in typical early implementations, but Hanz Camenzind has stated that the number was arbitrary. The part is still in wide use, thanks to its ease of use, low price and good stability. Read more...

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A4 lever arch folderThis is a hard covered folder for holding any course notes you may write up, and for any diagrams you may draw.

It is important to get into the habit of writing up your notes on a regular basis. To that end, you are supplied with a spiral notebook and black and red pens. During induction, you will also purchase a geometry set and a pack of markers.

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A4 refill padsDuring your phase 2 training, it is important that you take and write good notes on the course material. You should also get used to drawing detailed diagrams of vehicle and machine components.

In order to help you do this, you will be issued, free of charge, a spiral notebook and an A4 refill pad. As you fill these pads and notebooks, you will be given new replacement items, also free of charge.

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Advanced Automotive Engineer.

This is a qualification awarded by the Institute of the Motor Industry.

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Anti blockier system, or anti-lock braking system, an electronically controlled system that senses the relative speeds of road wheels in order to determine whether braking wheels have locked up and began to skid. If they have, the system overrides the braking effort supplied by the driver, and frees the brakes until the wheel begins to turn again (stop skidding).

The system is informed by speed sensors at the wheels. These same sensors can be used to feed into a traction control system.

Check here for more information.

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Acceleration is simply a change in speed.

Acceleration can be positive - an object speeds up, or it can be negative - an object slows down.

The kind of acceleration we all experience every day is the acceleration produced by gravity - 9.81m/s2, referred to as 'g' in engineering calculations.

For example, in order to calculate the weight of an object, we multiply its mass by the acceleration produced by gravity:

W=m.g

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Acid-proof apronDuring Phase 2, you will spend a lot of time working with lead-acid batteries. In order to protect your body and clothing from acid, you will be issued with an acid-proof apron.

You will also be issued with acid-proof gloves to protect your hands against acid.

You should wear the gloves, apron and your safety goggles whenever you work with lead-acid batteries.

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Acid-proof glovesDuring Phase 2, you will spend a lot of time working with lead-acid batteries. In order to protect your hands from acid, you will be issued with acid-proof gloves.

You will also be issued with an acid-proof apron to protect against acid spillages.

You should wear the gloves, apron and your safety goggles whenever you work with lead-acid batteries.

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This alerts the operator or the service technician that an electronic system malfunction is currently present. Refer to the term Diagnostic Code in this glossary.
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Ackermann angle

Imaginary lines drawn through the king pin and the track control rod end on each side of a vehicle will intersect at a point just in front of the rear axle of that vehicle. The angle they make with each other is known as the Ackermann angle.

The purpose of the angle is to allow the front wheels to turn through different angles when cornering. This is because the inside wheel always needs to turn through a bigger angle in order to get around the corner without scrubbing.

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Word formed by using the first letter of other words, for example:

RAM-Random Access Memory

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Pressure sensors - active sensorsUnlike a passive sensor, an active sensor needs a power supply. There are 3 terminals on a pressure sensor. One is a supply, one is ground, and the third sends a signal back to the ECM.

Here, we can see the example of a pressure sensor. There are 3 terminals. We know this is an active sensor because it has these 3 terminals.

  1. Pin A is a 5 volt supply into the sensor.
  2. Pin B is common, meaning it is grounded to 0 volts.
  3. Pin C sends a signal back to the ECM. From this signal, the ECM calculates the pressure acting on the sensor.
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In certain course modules, such as the small plant module, there are activity sheets for you to download. Once you do this, you should work your way through the sheet, carrying out all the activities listed, and researching answers to all the qeustions asked by searching this website, your own course notes and the world wide web.

The small plant module covers a large range of machinery, so it can be very difficult to cover everything.

Acitvity sheets will guide you to study all matters related to health and safety, theory and practical work. If you do all activity sheets, you will not come across anything in the practical or theory exams that you have not already researched as you worked your way through the activity sheets.

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Acupuncture probe in useA needle-like probe used in automotive diagnostics when probing wires and connector blocks for electrical signals.

It is very easy to cause damage to wires, their insulation and to connector blocks when trying to diagnose electrical problems. You must make good metal to metal contact with electrical circuits to analyse them, but it is essential you do not cause any damage when doing so.

An acupuncture probe is smooth and pointed, allowing you to slide the probe into connector blocks without causing damage. The probe then connects to your voltmeter or oscilloscope by way of the standard 4mm connector.

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This denotes a self-learning system.
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This is a software process that is performed in the ECM that optimises engine performance.
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Sometimes, course participants may feel they can add more to an explanation given in this glossary. In cases like this, they can add comments. See the comment at the bottom of this entry. (Please note: comments are only visible to registered users who are logged in.)
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This is content over and above what is on the Phase 2 syllabus for CP Fitters.
It is sometimes posted on the site in order to help apprentices who may wish to find out a little more about certain topics or equipment that is covered during Phase 2.
Additional content will not appear in any Phase 2 examinations.
You need only view additional content if you want to broaden or deepen your knowledge about specific topics or pieces of equipment.

Example of Additional Content

During the Electrical Module, there is a learning unit called 'Lighting Circuits'. During this unit, you will build various wiring circuits. One such circuit is an indicator (turn signal) circuit.
This type of circuit originally used what was known as a 'hot-wire' flasher unit. Nowadays, these older type flasher units have been replaced by electronic version.
If you would like to learn more about these more modern units, there is a page of additional information with an overview, links to data sheets and a video of the operation of a typical electronic flasher unit:
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Address bar in a browser windowThis is the part of a browser window into which you can type the URL (the web address) of a website. If you know the exact URL of a site, you should type it in here.
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