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Cable length limits for Dr DAQ external thermometer

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Cable length limits for Dr DAQ external thermometer

Postby sejones » Thu Nov 06, 2008 3:09 am

I wanted to measure the temperature at different pints in my house, but when I use an extension to the thermocouple line, I get screwy readings, like ******. Is there a limit to the cable length? If so, is there any other trick around it so I can measure temperatures at long distance?

Thanks
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Postby Robin » Mon Nov 10, 2008 9:53 am

Hello

Are you using a thermocouple or a thermistor? It is not possible to use thermocouples with DrDAQ, as there is no cold-junction compensation.

Assuming that you are using thermistors, the lengths that you are describing should be acceptable. The thermistor has a high resistance, so the added resistance of extra wire makes little difference.

Does the sensor work without the extension?

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Postby sejones » Tue Nov 11, 2008 2:55 am

Thanks Robin,

The temperature sensor is the one that was provided with DrDAQ, so I presume it must be the themistor.

The sonsor works without the extension, but as I add cable lengths, the answer becomes more strange. For example, with an additional 10 ft, the temperature is about 80 degress off, then with an extra 50 ft, the reading starts off fine, but every second gets higher, into the 100s, then finally off-scale, reading "****". It's almost as if there is some type of power/current limit being reached.

I agree, I would have thought the device has high impedence, so the long cable lengths would not be that much an issue, but it seems to be.

Does this make sense?

Thanks,

Steve
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Postby Robin » Wed Nov 12, 2008 11:32 am

Steve

I'm not sure why you're getting such strange results. Have you measured the resistance with and without the extension connected? Is there any equipment nearby that could be interfering?

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