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Suggested method of '''EGT input''' calibration / verification. Needed: * DVM * 2 resistors ( with a ratio of 100-500, like 4k7 and 1Mohm ) or sensor in gas-flame For offset-calibration, only an alligator clip is needed. ---- Round device '''typical EGT calibration value''': 157 (0x9d). If calibrating, start from this. Calibration is for device input, NOT the sensor. No need to calibrate if using with a different sensor. Recently (since 2008-03) EGT input is calibrated. (the default value gives smaller reproducible error than the error related to sensor placement). Calibration is useful verification any time one . ---- '''Offset calibration''' Before adjusting offset, make sure egt calibration has a reasonable (near 157 value, say +- 8). If it's way off, like 0 or 255, you will have to repeat offset step later, so better start with a reasonable offset. * '''attach 0mV''' to input (alligator clip between white and green) * start with '''offset =255'''. (EGT will read a bit high) * '''decrease offset''' (offset -= 2 for -1C) to a value '''until it displays the cold junction temp''', which is the end of green compensational cable (the green and white wires at the alligator clip) (eg. +27C) ** This step is easier if EGT is displayed on bottom, but can be watched in megatune. offset: 0-255 (device dependent, no typical value) Now follow to EGT calibration step: ---- '''EGT calibration with 15-45mV signal''' A voltage divider (or hot EGT sensor) can be used to provide a small appr 30 mV signal. Maybe divide from a 4V signal (eg. temporarily steal from wbo2 pump- ), * 1k between green wire and GND * 100k between green wire and 4V result: 4V * 1k / (100k + 1k) = 39.6mV * white: 0mV * green: +39.6mV '''measure''' this with DVM (digital voltmeter) example calculation: This 39.6mV is equivalent to 39.6 * 25C + 27C = 990C + 27C = 1017C (where +27C is the cold junction temperature). '''Adjust EGT calibration''' until reading is 1017C. That's all. Attach the alligator-clip again (0mV) and verify that cold-junction temperature is still OK. (if offset was adjusted with a weird calibration value, it might be off now: than go back to offset adjustment). Take note of the offset and calibration values for future reference (with permanent pen on the side or on a white tape on a cable). ---- '''Ice / Boiling water''' - because of the 100C (=4mV) not as precise as the 15-45mV signal above Set the offset to 255 and the calibration to 157. Adjust the calibration until you get a 100degree difference between the ice and boiling water - then use the offset to set the temperature so that it reads 0 in ice, and check the boiling water temperature to ensure that the temps are scaling properly. ----
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