# I Calculate the temperature based on Resistance

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1. May 26, 2016

### Elvira

Hello experts...
I have an experiment pool boiling. The test section filled with DI water, and use thin flat copper as the heater that connected to the power supply.

I want to ask how to measure or calculate the heater temperature if I only have the resistance, voltage and current data reading from the power supply.

As I observed it's not accurate if I attach thermalcouple to the surface of the heater, because the temperature will be different in every location (not uniform)

Thank you so much and have a good day

2. May 26, 2016

### Simon Bridge

Welcome to PF;
Knowing two of R,V,I you can find the rate that energy is dissipated in the heater ... the temperature also depends on the temperature of the surroundings.

Note: since you observe that the temperature reading via a thermocouple is not uniform across the heater, then the heater probably does not have just one temperature to find. Do you have good reason to think the heater should have uniform temperature?

What is the experiment supposed to find out?

3. May 26, 2016

### Elvira

Thank you Mr. SImon,
I 've tried to attached thermocouple in the edge and also in the middle, and they both have different reading.
I've read one paper and they mentioned that they just calculate the temperature based on the resistance then calibrate it.
So, I have no idea how will I get the accurate temperature reading for this case. I was thinking to attached the thermocouple on the surface by solder. Then put epoxy for the insulation and get the linear function (excel) then after that I can use the function for all experiment for calculate the temperature based on resistance.

But Im not so sure if Im right. That is why Im asking it here and needs expert opinion like you.
Thank you so much Mr. Simon.

Regards,

:: Vira ::

4. May 26, 2016

### Staff: Mentor

The resistance will depend on the temperature distribution, so you can get some measurement. Relating that to a single temperature value will probably not work, as different parts will have a different temperature and the distribution does not have to be the same in all setups. You can calibrate it with the thermocouples, if you follow exactly the same heating procedure every time this should give a reasonable estimate for the temperatures.

5. May 26, 2016

### Simon Bridge

The thermocouple has an internal resistance that depends on temperature - you also have a flat metal plate that you are using as a heater: this also has a resistance. The heater plate will, in general, have different temperatures at different places.

The thermocouples are being accurate ... you are getting accurate temperature measurements.
The heater really does have a different temperature at different places.

How you deal with that depends on what the experiment is supposed to be doing.

6. May 26, 2016

### edguy99

You may want to look at the COMSOL simulation program. One of their demo samples uses a copper filament and is pretty close to this.