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Old 08-01-2005, 06:01 PM
Tech Apprentice
Join Date: May 2003
Location: Melbourne
Posts: 55

Just had a look at the PE-1 at the link you posted and I have noticed a few things to be careful of.

The emissivity appears to be set at a fixed value of 0.95. This is a bad thing because the emisivity of a nice shiny piece of metal is usually closer to about 0.50 or less. I know this probably sounds a bit confusing and makes no sense but, what this means is that depending on the way the instrument is designed you could be getting errors of up to 20 Degrees celcius or more. I know that the manufacturer states the accuracy as 2 degrees celcius, I am sorry to tell you this but there is no way that can be anywhere close to true as I said above ten times that might be getting reasonable. The other thing to keep in mind is it has a field of view ratio of 1:1 this means that the target area expands by one inch for every inch you move away from the cylinder head. This means that you MUST get as close to the glow plug as possible because if the target area expands beyond what you are trying to measure the results will be plain wrong.

Now you ask what is a thermocouple, in short it is the thermometers that you can get that have the little wires you can hang around the cylinder head. These are realy good in many ways, because they are always attached they can record the temperatures during a lap or race, this peak temperature is far more interesting to you then the temperature of the glow plug after the engine has started to cool down. I know that a lot of people complain that the thermocouple only measures the air around the cylinder head but, this is easily fixed if you take that loop of wire and place it between the head and the screws that hold the head in place and use the screws to clamp the wire against the head. This means that you are now measuring the temperature of the head and not the glow plug but this is ok because most of the rules of thumb for tunning according to engine temperature where developed before infared thermometers where easily available and so are based on the cylinder head temperature not the glow plug temperature. If you suddenly change to using an infared thermometer you introducing another error into you measurment just because you have changed technique.

I hope this dosn't cause too much trouble but there are a lot of things to be aware of when changing to infared thermometers.

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