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



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Gustav Kirchoff, image from WikipediaGustav Kirchoff, a German physicist, responsible for two electrical laws:

  • Kirchhoff's current law
    Current going into a circuit is always equal to the current coming out of a circuit - in other words, any electricity that goes into a circuit, must come back out of that circuit. 
  • Kirchhoff's voltage law
    In an electrical circuit, the total sum of the individual voltage drops is always equal to the supply voltage.
    For example, if you have a voltage of, say, 12V on a circuit with a single electrical load, and you measure the voltage drop across the load at 11V, this means that you are dropping 1V elsewhere in the circuit and you have a problem.
    Voltage drop in a circuit is unavoidable, so we have acceptable limits.
    For the live part of a circuit, the limit is approximately 0.25V (up to 0.5V in starter motor circuits).
    For the earth part of the circuit, the voltage drop should be 0V, or very close to it.

You can read more about Gustav Kirchhoff on Wikipedia

You can read more about Kirchhoff's circuit laws on Wikipedia

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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

  • The weight of an object is measured in newtons, N, which is a base derived SI unit.
  • The mass of an object is measured in kilogrammes, kg, which is a base SI unit.
  • The acceleration produced by gravity is measured in metres per second, m/s, which is a base derived SI unit.
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Represented in datasheets with the abbreviation Iq, quiescent current is the current used by a device when it is ready to operate, but not yet supplying any current to a load.

You can think of quiescent current as the current required have a device ready to perform a task, but not yet performing that task.

You could also think of it as the current used by a component when it is powered up, but not yet operating.

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In the context of LEDs, each of them has a value called 'forward voltage'.
This is the voltage that must be put on the anode of the diode in order for current to begin to flow through the diode.
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When the anode of a diode is connected to a positive supply, and the cathode to a negative supply, the diode is said to be forward-biased. The diode will tend to conduct in this condition.

For the diode to actually conduct in this condition, (forward biased), the voltage must reach a certain minimum level before any current flows. This value for a diode is known as its 'forward voltage'.

When these connections are reversed, and the anode is connected to the negative supply and cathode is connected to the positive supply, the diode is said to be reverse-biased. The diode will not conduct in this condition.

It should be noted that when a diode is reverse-biased, there is always a certain amount of 'leakage'. In addition, if the reverse voltage is high enough, the diode will break down and will conduct in the reverse direction (for example, a zener diode). Other ordinary diodes can be destroyed by being subjected to excessive reverse voltage.

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From the Aerial Platform Hire website:

Aerial Platform Hire is Ireland's leading work platform rental company. Founded in 1980 we offer for hire self propelled boom and scissor lifts manufactured mainly by JLG industries, the worlds largest manufacturer of powered access equipment. We also offer Telescopic Handlers from JLG and Manitou Buggiscopics. Hire is available from strategically located depots in Clane, Co. Kildare and Mallow, Co. Cork. We deliver machines throughout Ireland from both of these depots.

Read more...

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Edina logoEdina is the sole distributor for Perkins engines in Ireland.

Edina locations and contact details in Ireland and the UK.


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DDLETB

This is the educational institution that currently has responsibility for the provision of Phase 2 apprenticeship training in the trade of construction plant fitting.

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Of the seven phases of training for the CP apprentice, four of them are delivered 'on the job', in the apprentice's place of employment. These phases are 1, 3, 5 and 7.

The even numbered phases (2, 4 and 6) are known as the 'off the job' phases, and are currently delivered by DDLETB (Phase 2), and by the Cork Institute of Techonology (CIT), who deliver phases 4 and 6.

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Cross-sectional view of a lip sealLip Seals and Oil Seals

The diagram on the right here is a cross-sectional view of a lip seal.

Oil seals used to seal running shafts are known as dynamic seals. The main seal you will come across during the engine disassembly exercise is the crankshaft oil seal. The seal shown here has a circular spring to help it maintain a good seal. The lip of the seal should be soft and pliable. The steel casing allows the seal to be pressed into a housing.

When you are inspecting this seal, make a visual inspection to make sure there are not cuts or marks on the lip of the seal. Also, don't forget to inspect the pulley or shaft surface that the seal runs against. This can become worn or damaged.

Typical lip spring showing details of the spring that keeps the lip of the seal in contact with whatever it is sealing

Cross-sectional view of a fitted oil sealHere we can see how the steel spring keeps the lip of the seal pressed against the surface of the crankshaft pulley.

Note the oil slinger fitted behind the oil seal.

When fitting new seals, remember to inspect the pulley surface as well. The pulley forms half the seal.

Cross-sectional diagram showing how oil pressure helps the seal to function

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