Varied Resistance for a Certain Temperature

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thunderdog116
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Varied Resistance for a Certain Temperature

Post by thunderdog116 » January 8th, 2020, 11:00 am

Hi, I've created a thermistor that's waterproofed and had been working well. Yet, now one day the thermistor for example outputs a value of 30000 ohms for 25 celcius, and then the next day might output 350000 ohms, which is very odd). Does this mean I should rebuild my device instead of focusing on calibration.

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Re: Varied Resistance for a Certain Temperature

Post by waterlubber » January 10th, 2020, 2:36 pm

You probably have a loose wire or connection, or a busted thermistor. Thermistors should output the same resistance for the same temperature (and do quite reliably), so if you're getting results like that you need to find where your error is.
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Re: Varied Resistance for a Certain Temperature

Post by rabbitman » January 14th, 2020, 5:57 am

I have the same problem, if someone has determined the cause, please consider sharing. I think it is because either my sensor is trash or my waterproofing is sketchy.

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Re: Varied Resistance for a Certain Temperature

Post by YeagerTheCat » January 14th, 2020, 9:45 am

rabbitman wrote: I have the same problem, if someone has determined the cause, please consider sharing. I think it is because either my sensor is trash or my waterproofing is sketchy.
If the resistance drops, then you likely have water getting into your connections to the thermistor. If the resistance goes up, you likely have some issues with your connection to the thermistor (eg dodgy solder joint, wire issue). Thermistors are not indestructible but they are not weak either.

Hope this helps,

YtC

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Re: Varied Resistance for a Certain Temperature

Post by thunderdog116 » March 4th, 2020, 5:24 pm

I realized when I moved the wiring connecting the circuit board to the arduino the readings changed. It was probably due to the connection to the circuit board, so I hot glued the wires to the circuit board so they would stay in place. Sorry, for the really late response.

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Re: Varied Resistance for a Certain Temperature

Post by arazborov » March 4th, 2020, 7:11 pm

Hot gluing the wires to the circuit board (or breadboard) isn't such a great idea... If you are having this problem you should probably use jumpers or directly solder to the board (if you have some spares).

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Re: Varied Resistance for a Certain Temperature

Post by MTV<=>Operator » March 5th, 2020, 7:58 am

The thermistors that I use have really thin leads, and previously I had been connecting them to two male-female wires and coating this with waterproofing, but this doesn't seem to create a reliable connection. Would it be better to just solder the leads to wires? I'm worried that the heat required to apply the heat shrinks would melt the solder
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