problem with NTC setup

[nicoawd]

hello ArT,

I have a problem with NTC sensor again: I installed a third sensor to monitor engine water temperature, connected the sensor white wire to car's chassis and sensor's blue wire to pin B2 Adc3 in Utcomp(the last vcc position available). in the input/output menu I selected NTC3 in the B2 courtain menu, then assigned engine temperature to NTC3 in the NTC calibration page. I entered the same calibration values used for the 2 other sensors(that are perfectly working): R25=47000 B=3800. unfortunately the value displayed on the screen is constantly -273.
I tried to disconnect the signal(blue) wire and reading went from -273 to +300 so it should not be a problem of missing signal. I tried to connect the negative wire(white wire) directly to negative wire in Utcomp instead of using car chassis but nothing changed, so I tried to disconnect the negative wire and the reading did not change(-273). is my problem here a missing negative connection? since I connected the white wire to the car chassis and also directly to Utcomp negative wire I assume it's not the connection that is missing: should I suppose the sensor is not working?

[ArT]

Hi Nico,

You should connect sensor to AdcVcc1 or AdcVcc2.
Adc3 does not support NTC sensor which is not connected to ECU already.
If you do not have any left from AdcVcc1 or AdcVcc2 you can modify Adc3 input to AdcVcc input.
You will need to add 1000 ohm resistor (1%) between signal (blue wire in your case) and +5V line. You can use +5V from DS18B20_VCC output, it's not exactly 5.0V but it should work too.

[nicoawd]

I tried the 1000 ohm resistor trick but I do not have a true reading: displayed value changed from -273 to 5 degrees while the other fluids(oil and intercooler water) displayed 21(engine not started yet) so 16° difference. after driving the car uphill with the fan running(running at slow speed), displayed water temperature was 35° so assuming a 16° difference it would make 51° that seems to be too low to have the fan running even if it's running at the slowest speed. do you think it's a matter of calibration or I have to use a different resistor? calibration used is the same as other ntc sensor I use: R25 47000 and B 3800

[ArT]

Are you sure that you have used 1000ohm resistor? What's your DS18B20_VCC output?

[nicoawd]

I tried to search on the internet to check the colours of my resistors and it seems like brown black red gold should be 1k ohm: I assume it's not possible to read it the other way around since I did not find anything starting with gold. since it's the first time I use such object I do not know if I can connect it in both ways or it gives a different result if connected reversed. since I insulated it with heat shrink I could not see how it is orientated. I simply soldered 2 pieces of wire to the resistor and connected the wires to b12(it was not a free position so it is supplying 5V to 2 sensors) and B2

[ArT]

It's 1kOhm with 5% tolerance, so it can be 950-1050 ohms. It can be connected in both ways, it does not matter. Do you have multimeter to measure resistance of resistor and measure voltage on B12 output? So I can calculate you better scaling parameters for this case.

[nicoawd]

I made the measurements and found that with engine running, the voltage output at pin B12 is between 4,83 and 4,84 volts and the real resistence of my resistor is actually is 982-983. can this difference from nominal values give me wrong readings on the temperature displayed on the screen?

[ArT]

Yes it can be the difference, but from my calculations you should read higher temperate not lower because you will have slightly lower voltage on sensor (lower voltage = higher temperature) so it all does not make sense. I can't figure out where is the issue, but I suppose that DS18B20_VCC is not a good voltage reference when you have connected any DS sensors. Could you open UTCOMP and make this mod inside so you will get voltage from inside instead of from DS18B20_VCC? so you will get exactly VREF (around 5,2V).

I marked you where you should connect 1k ohm resistor inside (between Adc3 and VCC). Please protect it to not touch to other pins.