# Figuring resistance and temperature

1. Aug 21, 2010

### ISX

I am trying to make a calculator to figure the temperature based on the ohm reading. I have done a lot of measuring with the sensor I am using and the results are in the excel. I tried calculating it with y=mx+b since it is linear but for some reason it doesn't seem to work. Any ideas?

Here is a pic of the excel if you don't want to download it.

http://i38.tinypic.com/1phykz.jpg

#### Attached Files:

• ###### OhmsandDegrees.xls
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Last edited: Aug 21, 2010
2. Aug 22, 2010

### HallsofIvy

Have you graphed those points? (Excel should be able to do that for you.)

Does the graph look like anything familiar? If it is a straight line, it would be easy. If it looks like a parabola, cubic, exponential, etc. you can write out the general formula for such, the put in enough of your values to determine what the constants in the formula are.

3. Aug 22, 2010

### physret

Plotting a scatter plot in Excel gives not a straight line but a downward curve, something like a falling exponential or perhaps y = 1/x. y = mx+b won't fit well even with negative m. The fact that resistance decreases with temperature suggests that your sensor is a thermistor (or other semiconductor device), and thermistors are not linear. Metal wires have resistance that increases with temperature linearly for a moderate range. You might find a suitable equation for your sensor on spec sheets for thermistors or other semiconductor temperature sensors.