An insight

One observant instrument user has noticed that our EGT/CHT readings tend to be higher than with ordinary gauges - Why is that ?

Our EGT/CHT gauges, like all others are based on thermocouples. Instruments based on these devices can only read correctly if the temperature of the "cold junction" (i.e. the terminals where the thermocouple connects to the instrument) is known. The instrument needs to measure this temperature and it needs to be taken into account in the overall calculation of the temperature at the tip of the thermocouple.

It may surprise you, but very, very few instruments do this. It is common practice to adjust the instrument during manufacture so it reads correctly with the instrument at zero degrees Celsius (the Ice point). This unfortunately means there is an error if the temperature of the instrument is not at zero degrees. For example, should you be at a more manageable 25 degrees Celsius - your instrument will UNDER READ by about 25 degrees !!! Our instruments have very high measurement resolution, normally only found in laboratory instruments and they compensate for the local temperature. This is called "Cold junction compensation". As a result our readings are very accurate and this does not change with ambient temperature as the instrument automatically adjusts itself.

A further, unusual measure found in our instruments related to measuring temperatures, is that the amplifier used to amplify the very small voltages from the thermocouples is itself measured for errors caused by ageing and drift - and these are corrected for in the measurement result.

 

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