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Kelvin leads for DMM
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BillyO:

--- Quote from: Electro Fan on August 30, 2023, 03:07:07 am ---Yes, it is.  Do you think the AC comes and goes that symmetrically?  Seems slightly hard to believe but maybe....

--- End quote ---
Your collection was over only 2 hours so the external temperature likely would not have changed much in which case the AC would cycle fairly regularly.  As for symmetry .. luck of the draw in most cases but to be expected for a well designed system.

One way to test would be turn the AC off for a couple of hours and re-run the data collection.
Electro Fan:
Ok, fwiw, since my earlier post I went back to run the 45 cm 18 AWG copper wire test.  Below is the trend chart for that; doesn't appear quite so symmetrical but it's only about 9.6 milliohms vs roughly 150 milliohms for the 45 cm 30 AWG kynar wire.

I have restarted the kynar wire test and I'm going to shut the AC off and let the room warm up.  We'll see what that looks like after the test runs for awhile.
mawyatt:

--- Quote from: Electro Fan on August 30, 2023, 03:07:07 am ---
Yes, it is.  Do you think the AC comes and goes that symmetrically?  Seems slightly hard to believe but maybe....

--- End quote ---

Our AC operates on a "Bang-Bang Servo" concept, where the AC comes ON until a lower set temperature is achieved, then OFF until a higher set temperature occurs, then the cycle repeats. The AC period is shorter during the day, but longer at night when the outside is cooler.

Copper has a very high TC and thus becomes a temperature sensor rather than a fixed stable resistor. You can cover the entire measurement with a blanket or thermal insulating box, this will reduce the measurement excursions.

If you have another plotting meter, get a thermistor and plot the temperature along with the measurement, they should correlate well.

Best,
Electro Fan:

--- Quote from: mawyatt on August 30, 2023, 01:52:20 pm ---
--- Quote from: Electro Fan on August 30, 2023, 03:07:07 am ---
Yes, it is.  Do you think the AC comes and goes that symmetrically?  Seems slightly hard to believe but maybe....

--- End quote ---

Our AC operates on a "Bang-Bang Servo" concept, where the AC comes ON until a lower set temperature is achieved, then OFF until a higher set temperature occurs, then the cycle repeats. The AC period is shorter during the day, but longer at night when the outside is cooler.

Copper has a very high TC and thus becomes a temperature sensor rather than a fixed stable resistor. You can cover the entire measurement with a blanket or thermal insulating box, this will reduce the measurement excursions.

If you have another plotting meter, get a thermistor and plot the temperature along with the measurement, they should correlate well.

Best,

--- End quote ---

Thanks for your post.  I didn't see it until just now so the measurements have been running overnight since my last post with the AC off.

Here is the latest....

Electro Fan:
Looks like the symmetric pattern was just the Air Conditioning cycling on and off.

I haven't given as much attention to the exact room temperature as I should have but my guess is that overnight the room reached about 78F and since I turned the AC back on it's been cycling just a little above and below 74F (the current target temp).

No doubt there is a relationship between resistance and temperature.   :-+
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