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I am continuously measuring resistances of certain organic materials (resistances anywhere from 30ohms to 15Mohms) using a 2 point method. The idea is to study change in resistance as a function of temperature and time (the experiments last ~10-20 mins). I have noticed some sort of drift in the measurements, and I was hoping I could get some advice as to cancel out this drift. The image below shows that resistance (red curve) changes even though the temperature of the sample isn't changing.
Basically, I set the source voltage to 1V, and I have auto-settle and auto-zero on. I have tried different keithleys, and I see the same thing, so there is something wrong with my set-up or the way I'm measuring. Any help would be appreciated.
- Keithley Applications
- Posts: 1323
- Joined: October 15th, 2010, 10:35 am
- Country: United States
For the low resistance values (less than 100Ω) you should use 4-wire ohms connections. This will eliminate effect of the lead wires.
For your room temperature data, you have change of about 300mΩ which is a full order of magnitude larger than what you'd expect from the 2V source range and the 100mA measure range of the 2400 for an ideal 39Ω DUT. The total error could be coming from multiple contributors, such as thermal drift in any dissimilar metal junctions in your connections.
You might want to access just the drift/stability of the 2400 with a simulated 39Ω DUT (discrete resistor) connected directly to the instrument terminals.
Try testing a real resistor -- do those readings drift ?
Try force a higher R range (which uses a smaller test current). You'll lose resolution/accuracy, but maybe thats OK ?
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