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Identify a temp sensor without removing it. — Parallax Forums

Identify a temp sensor without removing it.

jdoleckijdolecki Posts: 717
edited 2022-11-03 17:02 in General Discussion

Is there a way to test/ measure a temp sensor in circuit without removing it?

The sensor is on the output hose of my laser head. I have verified I’m getting chilled water to it. But I can’t get my temp alarm to reset sometimes on the controller.

Is it just measuring the resistance of it and ordering a new one? What other specs do I need to know.

I have no schematics for this.

Comments

  • Tricky situation. If you measure the resistance of a defective temperature sensor you will not buy the right one. There are no guarantees that the sensor has any useful markings either.

    An intermittent problem might be a loose connection.

    Maybe what you could do is connect a dual gang potentiometer in place of the sensor. Dual gang potentiometers would most frequently be used for stereo volume control. The log taper shouldn't be a big problem here. That way you can read the resistance of one side while the other side emulates a thermistor.

    It may be worthwhile to check for resistance between the sensor wires and the fluid. I would imagine the a sensor is supposed to be insulated from the fluid.

  • Could be a RTD or thermisistor

  • Your will likely need to remove the part unless the maker supplies you with the part number. From there you can find the Temp to resistance graph to see if the device is working at all and if so, does it track the expected values for a given temp range. If you have to remove the part, hopefully the markings are still on it. Best bet though is to just order one from the manufacturer if they will sell it to you. There is no reliable test without the part data sheet. Same issues with my hot tub, but I can get third party parts for it. AS when the high limit thermister failed.

  • @SaucySoliton said:
    Tricky situation. If you measure the resistance of a defective temperature sensor you will not buy the right one. There are no guarantees that the sensor has any useful markings either.

    An intermittent problem might be a loose connection.

    Maybe what you could do is connect a dual gang potentiometer in place of the sensor. Dual gang potentiometers would most frequently be used for stereo volume control. The log taper shouldn't be a big problem here. That way you can read the resistance of one side while the other side emulates a thermistor.

    It may be worthwhile to check for resistance between the sensor wires and the fluid. I would imagine the a sensor is supposed to be insulated from the fluid.

    I pretty sure the sen

  • evanhevanh Posts: 13,852
    edited 2022-11-05 23:00

    I would say it's almost certainly a thermistor. Pt100/1000 are expensive so only get used for precision applications. And thermocouple wires are stiff and always colour coded.

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