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Topic: Which Cable should i use? (Read 418 times) previous topic - next topic

motomoto2

Hy

I want to place a LM35DZ temperature sensor 5 m away and need a 5m cable. I have already bought a cable (specifics in the pdf), but when connected the received signal jumps around like crazy (more too low than too high but also too high).

I would like to know which type of cable I should use in the first place, if the one I bought is useable and if anybody can lead my to a tutorial on choosing the right sensor cable as I didnt find anything on the web.

Thanks

MarkT

I presume you are using 2 cores in the cable, one for supply and one for the output, screen is ground?
There will be some small systematic error due to the IR drop across the ground screen, but its probably
negligible.

The low level of the signal (10mV / C) means that even small amounts of pick-up are an issue - fortunately
temperature is a slowly varying quantity so low-pass-filtering ought to be able to lose a lot of the noise.
Perhaps just adding a 100nF capacitor across the output would be a good start, try with a 10k resistor in
series too.  If you bring the noise bandwidth down to 1Hz or less it should make a dramatic difference.
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