I have three temp sensors. CLT, IAT and EGT. And I want to calibrate them. I allready ordered a digital thermometer. So I can calibrate CLT and IAT.
EGT calibraion
Look at http://vems.hu/www.vems.co.uk/VEMS/egt.html Step 5.
Cold is easy: short the EGT inputs (eg. alligator clips) and verify offset is reasonable (reading appr. the same as the temp of EGT input, within a few degrees). Let's say it's 20C and you read 15C (it won't be precise enough for human body temp measurement, but perfect for EGT).
Knowing the K-thermocouple slope: 40uV/C, that is +40mV between EGT inputs => +1000C (that is 1015C reading if the v3 temperature is 15C), you can finetune the egt_cal (0x49 .. 0x4a are most common IIRC). You can apply 15..50 mV with a voltage divider. The exact value does not count, just measure with your DVM so you can divide it by 40uV/C to get the delta-temp in C.
And I have an open IAT sensor. Can i put this one in hot water also?
- IMHO as long as you plan to use it on a turboed engine it should handle high temperatures and water otherwise it's can't keep up with the planned application.
With an NTC type IAT, take a v3 readings
- at a known temp between 0..30C (eg. 25C). Than we can calculate resistance(temp) curve quite precisely.
- with a 1k (or even lower) fixed resistor in place of the sensor
- take note of what firmware version you used (publish the vems.hex or at least the 0..0x3FF part if it's a nonfactory hexpatched firmware).
We can help you finetune the curve than. Better than playing with hot liquids. If you really insist hot liquids, boil water and put the sensor into waste cooking oil on top of it (to avoid changing resistance with the conductivity of water). WhatEverYouDoYouDoItAtYourOwnRisk
Did some tests with clt sensor in water with digital thermometer and dvm. But I'm confused. This is what I measured:
30 degrees Celsius = 1713 Ohm
40 degrees Celsius = 1205 Ohm
50 degrees Celsius = 857 Ohm
60 degrees Celsius = 640 Ohm
100 degrees Celsius = 189 Ohm
When I calculate my sensors nominal resistance (at +25C) the way it is explained on the EasyTherm/SensorTable page. Everytime I get a really different outcome. At 100 degrees 2700 is the best choice. And at 40 degrees 2252 is the best choice. Is there something I'm doing wrong here?