MGL Avionics User Forum

Hi. Thanks Rainer for this function in my Enigma and this User Forum.

I've recently upgraded my Jabiru 3300 engine to Rotec Liquid Cooled Heads which is going well.

I've wired an auto coolant temp sensor into the RDAC coolant input and now need to configure it in my Enigma.

I've selected programmable probe in Coolant temperature setup as the one I bought is not one of the pre-configured ones.

The four digit calibration number I need to enter for each 20 degree increment does not have any units mentioned (on screen or in manual) and wont take an input > 4900.

Can someone please advise if the required entry is ohms, kilo-ohms, or something else?

Thanks
Darren

the number you are entering is the actual ADC raw reading that ranges from 0 to 4095 (12 bit ADC).
The raw reading can be obtained from your diagnostics menu once your sender is connected and you cycle it through the various temperatures - usually heating oil on a stove using a reference thermometer.
Another way is to use one of the many free circuit simulators if you know what the resistance curve vs temperature is. Construct a simple simulated circuit with two resistors in series with a DC power source. Make that source 4095 volts (or 4.095 volts if your simulator balks at the high voltage).
So now your two resistors in series go from the positive voltage source to ground. Now fix the value of the top resistor to 1500 ohms. That is the pull up resistor in the RDAC. The bottom one is your new probe. Enter the resistance from your curve in steps and "measure" the voltage over it. That is now your ADC value for that temperature. Enter those numbers in your Enigma and you should be fairly accurate.
Be aware that usually these probes have significant tolerances and are usually only reasonable around the target temperature which tends to be 100 degrees C for coolant probes and 120 degrees C for oil temperature probes.