MSgpio.com read only forums (Jan.15,2018)

That's a good point Lance..

Hi Lance, just revisiting this topic as my install is now complete so just need get this sorted.

I can confirm that my thermo sensor is fed 12v. I've just checked the resistance between the 12v supply and the thermo sensor output at 0.291Mohm. The Audi manual states 0.247Mohm @ 20c so that's about right considering the temp in my garage.

So what do I enter in TunerStudio?

Addicted,

What we want to enter is a temperature/resistance pair. TS works out the voltage from that resistance, using the bias resistor. The formula is:

Vsig = Vsup * (Rtherm/(Rtherm + Rbias))

where:
Vsup = supply voltage (the voltage supplied to the bias resistor)
Vsig = the signal voltage
Rtherm is the thermistor resistance at the given temperature, and
Rbias is the bias resistance

We need to calculate the equivalent resistance that will give us the same voltage that we have from your earlier specs:

20C - Ra = 247000, Rb = 3300, Vin = 15, Vout would be 0.198v, ADC 40
60C - Ra = 48800, Rb = 3300, Vin =15, Vout would be 0.95v, ADC 194
120C - Ra = 7400, Rb = 3300, Vin =15, Vout would be 4.63v, ADC 947

For example, take the last value: 120C and 4.63V

Lets also use the standard 2490 Ohm bias value (we could use other values, in the end it only matters that we are consistent). We'll spec it as a Vsup of 5 Volts (I'm not sure that TS will let you use 12V, and in any case our calculations will account for it).

So again, we want to know what resistance value will give us 4.63 Volts, and that's the resistance value we pair with 120C in the TS calibration menu (along with two others).

Well, with 2490 Ohms and 5Vsup, the equivalent resistance to get 4.63 volts would be:

Vsig = Vsup * (Rtherm/(Rtherm + Rbias))

4.63 = 5.00 * (Rtherm/(Rtherm + 2490))

4.63/5.00 = Rtherm/(Rtherm + 2490)

0.926 (Rtherm + 2490) = Rtherm

0.926 * Rtherm + 2305.7 = Rtherm

2305.7 = 0.074 Rtherm

Rtherm = 31158 Ohms

So the last point to enter is 120C, 31158 Ohms (specifying 2490 for the bias resistor and 5V for the supply voltage [aka. the "bias voltage"]).

The other two are done similarly.

Note that the resistance usually decreases in a thermistor as the temperature increases, and as a result the signal voltage drops with increasing temperature. Yours increases according to your table of values. However the given resistances appears to decrease, so you might have the resistor values mixed up, and 4.63 might really be 5.00-4.63 = 0.37, in which case the equivalent resistance value would be:

0.37/5.00 = Rtherm/(Rtherm + 2490)

0.074* Rtherm + 184.3 = Rtherm

Rthem = 199 Ohms

If the signal voltage actually does increase with temperature, I don't know how TS will handle that (i.e. what are it expectations, if any, are for the thermistor curve). You can try it and see.

Lance.

Thanks Lance, I had to read that a few times before it sank in

I've also asked the guys at EFI Analytics to see if they can shed a light also..

Addicted wrote: Doesn't seem to work though, its 17c in my garage and Tunerstudio is reporting about 60c..

Make sure there is no Celcius - Fahrenheit confusion. Last I checked the resistances for that sensor were in *F..

And I have a VW 01M in dire need of megashift.. I know this is no place to ask but how did you get all 7 of those silly Solenoids to function correctly? Is it possible (I have the standard Megashift GPIO board waiting for assembly).

Update.

Lance, your equation works!

Coolant temp in engine 18 degrees C, transmission fluid temp 17.7 degrees C


Thanks!

Great, I am glad it works!

Lance wrote: If the signal voltage actually does increase with temperature, I don't know how TS will handle that (i.e. what are it expectations, if any, are for the thermistor curve). You can try it and see.

Lance.

'thatswagenwagen' has tried it this weekend and Tunerstudio reads the temp as decreasing when its actually increasing