Temperature Coefficient of Resistance Science Project

Using Arduino Project Guidance
1

Hello all,

I am trying to do a science project for school measuring the temperature coefficient of resistance of copper wire. My plan is to submerge a coil of magnet wire (thermally conductive, electrically insulated) into a pot of water and adjust the temperature to adjust resistance. I'm not really sure how big of a difference my resistance will be, but I am approximating at about .85 ohms at 25 degrees C, and a change to maybe 1.1 ohms at 100 degrees C. I am attaching a diagram to show how I plan to set it up.

My biggest questions:

  1. Is this even practical for the arduino to measure these small changes such as this between these temperature levels? I know it measures at 5/1023 V resolution, but I'm just wondering if you guys think that's even enough?
  2. I know how to measure voltage with arduino, but since I am trying to solve for resistance, I can't really use it to solve for current with ohm's law. Is there a way to measure current with the arduino?
2

Attaching image isn't working well for me. I uploaded it to google photos. Schematic

3

It is very difficult to accurately measure resistance values that low, let alone small changes in those values.

One possibility is to increase the wire length to perhaps 1000 Ohms and use a Wheatstone bridge to measure the changes.

But without signal amplification, this project may be impossible using just an Arduino.

4

That's a cool suggestion, thanks. With 24 AWG copper wire, I should be getting about 85 ohms of resistance per 1000 meters at 20C , which is a lot of wire. The factor I have calculated is that a change from 20C to 100C will read 1.32328 times the resistance at 20C. To get to 1kOhms, I would need 11 km of wire :confused:

I can also think about exploring a low end, up to -80C with dry ice, extending my range a bit. I'll try to find something with the bridge that can work with something this small unless someone has another idea. Thanks!

5

With 38 AWG wire, you would have 2164 Ohms per 1000 meters. If the spool has both ends accessible, like mine, you don't have to unwind anything.

6

Oh, this is great. Thank you.

7

You can also use the internal bandgap for the Aref, at 1.1V you can measure more like 1mV per bit change instead of 4.88mV.
The analog input has to be under 1.1V then as well.

8

I'd dissect a relay, be an old cradle or reed relay, to get a coil of high resistance.

Using oil instead of water will result in a wider temperature range, and simplifies the insulation of the wires soldered to the immersed coil.

In either case a thermometer is required, because the boiling point of e.g. water depends on the atmospheric pressure. The Arduino can be used to also control the heater, for temperature stabilization.

9

electronic diy sites have circuits you can build to measure small low resistances or you can get special meters to do the same