# How to simulate a thermistor input without a thermistor

I would like to test one of a data acquisition modules. The input type is thermistor. I do not have a thermistor. I simply want to know if the module is able to read a temperature. I would like to know if it is possible to test the channel by just placing a jumper across the terminal(applying a 0 ohm resistance).
Thermistor module

Will this work? Is there a type of thermistor which has a known temperature at 0 ohms?

The module I am using has an interface to view the corresponding temperature value.

• Test with an R25 value, such as 10k, so just use a resistor instead of thermistor or even a potentiometer – sstobbe Jun 21 '17 at 22:00
• Yep, just use a know resistance and look it up on the thermsitor curve you have. – Voltage Spike Jun 21 '17 at 23:36
• 0 ohms would be a very high temperature for an NTC thermistor, off scale in the positive direction, and should probably be flagged as an erroneous reading in a well-designed system. – Spehro Pefhany Jun 22 '17 at 0:37
• You can use a simulator and calibrate with precision fixed R's .Thermistors come in a wide range of R values to reduce current in a bridge and wide range of tolerances. murata.com/en-us/tool/download/… or direct murata.com/en-us/tool/download/thermistor/download – Tony Stewart Sunnyskyguy EE75 Jun 22 '17 at 1:29

Thermistors are resistors with some reasonable level of resistance to be measured by a data acquisition system (DAQS). It would not be reasonable to try to test with zero ohms short.

The DAQS will typically be measuring the voltage drop across the thermistor when a current is biased through the device. Your proposed short circuit would imply no voltage to measure. It is not uncommon to bias a thermistor with a constant current. The known current makes it easy to use Ohms law to relate the measured voltage to the thermistor resistance. The other scheme used is to place the thermistor in a voltage divider with a fixed precision resistor that is then connected to a known fixed voltage. The DAQS reads the divider voltage and it is easy to compute the thermistor resistance using the voltage divider formula.

Care must be used to not put to much current through the thermistor part to minimize self heating. Self heating will clearly cause reading of the wrong temperature.

I would like to know if it is possible to test the channel by just placing a jumper across the terminal(applying a 0 ohm resistance).

Will this work? Is there a type of thermistor which has a known temperature at 0 ohms?

Not really, a zero ohm resistor will either read the max temperature or min temperature. There is a better way.

Generally thermistors are speced with a temperature and a resistance, like 25kΩ at 25C or 30kΩ at 25C or 10k at 25C (the thermistors are usually built to be a certian resistance at 25C (but can be other temperatures)). So all you would have to do is plug in 25k or 10k and watch the recorded temperature of the DAQ, it should be the same on all DAQ's you test, assuming that the DAQ's have the same thermistor constants in their software.

If you know the thermistor curve inside of the DAQ you could calculate what the temperature would be with a given resistor. Or you could experiment with trial and error. Start with 10k and then try 30k.

Thermistors have a curve, they are generally defined by 3 constants, A, B and C. This defines an exponential curve and defines the converstion of resistance to temperature. If the DAQ has the ability to change those constants then you could change them to the thermistor of your choice, and simulate the resistance. If you can't change those constants then that is ok, but you may want to do some research into how those equations work.