Poor Phidget 1048_0 resolution

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EddyQ
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Poor Phidget 1048_0 resolution

Postby EddyQ » Mon Mar 25, 2019 7:08 pm

I noticed recently that all 4 channels of my Phidget 1048 has poor 0.2deg C resolution. When temps fall slowly, I can see this with Phidgets Control Panel. Basically temps hold than then step downward 0.2C. Weird thing is, the temp does change slightly as it samples. I just updated the control panel tonight (build March 4th, 2019). The previous build was March 7th, 2018 and had the same issue. I tried a different USB on my laptop (didn't help). I'm running Windows 7 Pro 64bit.

Any clues as what would cause this? Anyone else have an issue like this? Could my 1048 gone bad?

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Patrick
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Re: Poor Phidget 1048_0 resolution

Postby Patrick » Tue Mar 26, 2019 10:31 am

The jitter you see is coming from the IC temperature sensor which measures the thermocouple junction temperature. Thermocouple temperature is calculated as a combination of the junction temperature and the voltage difference. You can see how they correspond by opening the IC sensor - it has ~+-0.05 degree noise at 32ms data interval.

The absolute resolution on the incoming voltage is 0.0015mV, which corresponds to ~0.04 degrees for a K-type thermocouple at ambient temperature. The resolution will be different at different temperatures and for different types of thermocouples.

You can verify this by plugging the board in, and waiting for the IC temperature to stabilize - this can take 5-10 minutes, as the board warms up. Then, set the data interval to 32ms, and watch the thermocouple temperature - you should not see jumps of 0.2 degrees, at least not for a K-type.

-Patrick

EddyQ
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Joined: Mon Mar 25, 2019 7:00 pm
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Re: Poor Phidget 1048_0 resolution

Postby EddyQ » Tue Mar 26, 2019 7:46 pm

Thanks for the fast reply Patrick

There are a few things that make me think it is not the IC sensor.
1) I see this on all three probes I have connected and the "step" happens at different times depending upon the probe.
2) This happens after very long periods of being on and running (very temperature stable
3) I just checked Phidgets control panel and the IC temp is stable and has no steps (even when a probe does have a step).

Today I received an 1045 IR sensor. I noticed when I connected it for the first time, USB drivers loaded. Then Phidget control panel connected. It is working great. When I connect the 1048, it never loads USB drivers. Could these drivers be re-loaded?


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