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


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L

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Leading Hull Artificer, a rank in the Irish Naval Service.

Read more about ranks in the Naval Service here

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In the context of diesel engines, the lag stage is the time between when atomised fuel is injected into the combustion chamber and the time when this fuel begins to burn. During this time, the fuel absorbs heat from the compressed air in the cylinder. No burning, and therefore no temperature or significant rise in pressure occurs during this period. The shorter this period of time, the less diesel knock there is in the engine.

This period is more commonly referred to as delay period.

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λ A letter from the Greek alphabet, often used in automotive engineering. When used in connection with tuning a petrol engine, when Lambda = 1, this represents stoichiometric, or chemically correct air to fuel ratio of 14.7: 1. The figure for diesel is approximately 14.5:1.

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Laminar Flow, Turbulent Flow:

  • Laminar flow describes when a fluid moves smoothly in a system.
  • Turbulent flow describes when fluid flow is unsettled and disturbed.

Read more here.

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A laminated iron coreIron is ferrous, and it is often used to concentrate magnetic lines of force into areas where they can do the most work.

For example, in igntion coils, both the primary windings and the secondary windings are wound around a laminated iron core. Likewise the armature windings in a starter motor are wrapped around a laminated iron core.

The reason why the core is laminated is that, besides concentrating magnetic lines of force into areas where they do useful work, these same lines of force inevitably move across the soft iron, thus iducing electricity in the soft iron.

This induced electricity will have its own magnetic field which will always oppose the magnetic field that induced it in the first place (Lenz's Law). These magnetic fields are known as eddys or eddy current.

This magnetic opposition can have undesirable effects - it can slow down the rate of collapse of the magnetic field around primary coil windings, causing a weak spark, or it can cause significant drag in motors.

In order to minimise the effect of these eddy currents, instead of using one solid mass of soft iron to concentrate magnetic flux, we use thin strips of soft iron laminated together.

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Local Area Network: A network of computers all inter-connected. The term 'local' suggests that whilst the machines are all connected to each other (either by means of a wireless or ethernet hub or access point), they are not connected to the internet.

If you check your network connection status on your machine, it will say 'local' or 'local and internet'.

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From page to page, file downloads may be offered. For example, there is a workshop manual available for the TS400 consaw. This file is around 14 Mb., which is relatively large - the link is shown as an example below:

Workshop manual for a Stihl TS400 consaw. (Workshop manual in PDF format, large download, about 14 Mb.)

It is a large document, so the large file size is unavoidable. The reason why the 'Large download' warning is put beside the download link is that files of this size can take a little time to download.

The speed of download depends on the speed of your internet connection, so it can take from 20-30 seconds up to a couple of minutes. There is nothing wrong with the link, it just takes a little time for the file to download.

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This refers to delay time. For example, a node on a CAN bus wanting to transmit a low priority message must wait until all higher priority messages have been transmitted. This waiting time, or delay time is called latency time.
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Latent just means 'hidden'.

During Phase 2, you will come across the word in 2 contexts:

  1. Latent heat of vaporisation: When you heat water, its temperature will rise. When the temperature reaches 100oC, the water will boil.
    If you keep heating the water, the water will continue to boil, but there will be no further rise in temperature. Because we know that energy cannot be created or destroyed, it must be doing something. We cannot see it by measuring the temperature of the water. However, the continued supply of energy is causing the water to boil and turn to vapour - steam vapour.
    Because we cannot immediately see and measure this temperature, we call it 'the latent heat of vaporisation'. Because we cannot immediately see this heat, we refer to it as 'latent' or simply 'hidden'.
  2. Asbestos fibres viewed under a microscopeThe Latent Period, Mesothelioma and Asbestos: Asbestos is a poor conductor of heat, and when asbestos is heated, its own properties do not change significantly. This made asbestos very useful and suitable for use as a heat insulator, and also for use in friction materials such as brake linings and clutch linings.
    However, when asbestos is broken down into very small particles (like when brake and clutch linings wear, or when we drill through asbestos used as an insulator), very small, spear like particles of asbestos become airborne.
    Because of the very sharp ends on these particles, when inhaled, become embedded in the lungs and remain there for many years. During this time, they don't cause problems, so we are not aware of their existence. However, after a latent or hidden period which can be as long as 30-40 years, these particles cause diseases such as mesothelioma.

    These conditions are inoperable and fatal.
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