heisan wrote:A thermocouple (as used to measure CHT and EGT) measures the difference in temperature between the probe and the 'cold junction' (the point where the thermocouple wire connects to the display)*.lessersg wrote:I have a question for the boffins.
Truth be told please------
Speaking to an instrument technician a few weeks ago, he indicated that it is the norm for the RDAC or any other make to measure the ambient temperature inside the cowl and add this to the CHT and EGT temp reading. Is anyone familiar with this equipment or can confirm this statement.
I do know that this happens with the MGL RDAC unless I misunderstood I did ask three times for an explanation ......
Old temperature gages just estimate environmental temp and display the result (so if the cold junction is 10 degrees hotter than normal, it will show 10 degrees *colder* than expected).
Modern EFIS systems though a re 'cold junction compensated' - there is a separate thermometer that measures that absolute temperature of the cold junction, adds the thermocouple relative temperature, and displays the real temperature (irrespective of environment temperature).
The MGL RDAC *is* cold junction compensated, so should be accurate in all conditions.
* NOTE: Some people extend thermocouple wires with copper wire. This moves the 'cold junction' to the join in the wire, and the resulting reading will be off by the difference between the temperature at the junction and the temperature at the instrument.
Ok if it adds the thermocouple relative temp how can it be a true temp reading of the cylinder head...