wiring an additional ntc

cosmowave

I have connected the ntc and it works more or less.
The only thing i know about the sensor that it is a 10k ntc. When i measure the resistence at 21°, it has a resistance of 11550 Ohm.
When i enter this in the config tool i get:
R10000 B3159 C0

So i configured the sensor with:

M308 S4 P"e6temp" Y"thermistor" A"TWater" T10000 B3159 C0   ; configure sensor4 as TWater, watertemp sensor

But the temp in dwc is more than 30° to high. And every time i restart the board, the temp is rising from a low value (-30°) to that value... with a curve like there is a capacitor to load...

cosmowave

Nobody a hint?
Eventually @dc42 can help me....?

droftarts

@cosmowave you can’t wire a thermistor directly to temp pins on the expansion header; they don’t have the necessary voltage divider circuit that is required to get a reading. See the Duet 2 schematic pdf for reference to build the circuit (last page, on the left) https://github.com/Duet3D/Duet-2-Hardware/blob/master/Duet2/Duet2v1.04/Duet2_1.04c_Schematic.pdf

I think all your doing at the moment is shorting vssa to ground, which is dragging down the voltage.

Ian

cosmowave

@droftarts Thank you very much for this info!
So, if i understand correct, i need to wire only the additional resistors to ADV-Ref?

dc42

@cosmowave to add a thermistor without using a DueX board, connect it between e6temp and vssa, and connect a reference resistor between e6temp and vref. A suitable value for the reference resistor is 2.2k. Specify the value of the reference resistor in the R parameter of the M308 command.

cosmowave

@dc42 Thank you very much. I will try that.

One more question:
Can i read and display (in DWC) a tacho signal without configuring a fan (in config.g)?
Or do i have to configure something like a "dummy fan" for the tacho signal?

dc42

@cosmowave you would need to configure a dummy fan.

cosmowave

@dc42 said in wiring an additional ntc:

@cosmowave to add a thermistor without using a DueX board, connect it between e6temp and vssa, and connect a reference resistor between e6temp and vref. A suitable value for the reference resistor is 2.2k. Specify the value of the reference resistor in the R parameter of the M308 command.

I've done that. But no improvement.
When i power the board, the temp is rising from a low value to a too high value with a "capacitor like" curve...

dc42

@cosmowave that may happen if neither the thermistor nor the resistor is connected to the pin. Please check that you are using the correct pin on the expansion connector.

cosmowave

@dc42 Sorry! my error.. i was thinking thermistor6 is e6temp.
Thanks again

dc42

@cosmowave does it work now?

cosmowave

@dc42 Yes! It's working!
Thanks a lot!