Basically, I'm looking for a temperature display around 4m from the sensor, wondering if I can just extend one I already have.
Cheap digital thermometer
Cheap digital thermometer
Cheap digital thermometers like the one pictured below, does anyone know if you can cut the wire, extend it by a couple of metres and maintain accuracy? The signal from the thermocouple will be microvolts so is voltage drop along wire important/calibrated for? Or is it insignificant as current is ~0?
Basically, I'm looking for a temperature display around 4m from the sensor, wondering if I can just extend one I already have.
Basically, I'm looking for a temperature display around 4m from the sensor, wondering if I can just extend one I already have.
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adam2
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- Joined: 02 Jul 2007, 17:49
- Location: North Somerset, twinned with Atlantis
Don't know.
BTW, I doubt that it contains a thermocouple. To determine temperature by use of thermocouples requires TWO thermocouples, one is the "cold" junction and for accurate work this is maintained at zero degrees by an ice/water mixture.
For measuring high temperatures, the cold junction is contained within the instrument and for calibration purposes is assumed to be at room temperature of say 20 degrees.
I suspect that cheap temperature indicators such as the one illustrated use a semiconductor sensor, the resistance of which varies with temperature.
In view of the low price of these I would be inclined to try extending the wire and see what happens.
Reasonably accurate calibration at 0 degrees* is possible with an ice/water mixture, and at 100 degrees* with boiling water.
At room temperature comparison with another device gives some idea of accuracy.
*for best accuracy, the 0 degrees calibration should be done with distilled water, and with ice made from distilled water. Clean tap water will give acceptable accuracy for non critical purposes.
The 100 degrees calibration should also preferably use distilled water, and for best accuracy should be corrected for the observed barometric pressure.
At close to sea level and avoiding extreme weather, the boiling point of tap water may be taken as 100 degrees for non critical purposes.
BTW, I doubt that it contains a thermocouple. To determine temperature by use of thermocouples requires TWO thermocouples, one is the "cold" junction and for accurate work this is maintained at zero degrees by an ice/water mixture.
For measuring high temperatures, the cold junction is contained within the instrument and for calibration purposes is assumed to be at room temperature of say 20 degrees.
I suspect that cheap temperature indicators such as the one illustrated use a semiconductor sensor, the resistance of which varies with temperature.
In view of the low price of these I would be inclined to try extending the wire and see what happens.
Reasonably accurate calibration at 0 degrees* is possible with an ice/water mixture, and at 100 degrees* with boiling water.
At room temperature comparison with another device gives some idea of accuracy.
*for best accuracy, the 0 degrees calibration should be done with distilled water, and with ice made from distilled water. Clean tap water will give acceptable accuracy for non critical purposes.
The 100 degrees calibration should also preferably use distilled water, and for best accuracy should be corrected for the observed barometric pressure.
At close to sea level and avoiding extreme weather, the boiling point of tap water may be taken as 100 degrees for non critical purposes.
"Installers and owners of emergency diesels must assume that they will have to run for a week or more"
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adam2
- Site Admin
- Posts: 11014
- Joined: 02 Jul 2007, 17:49
- Location: North Somerset, twinned with Atlantis
Alternative approaches include;
1) buy an instrument with a 2M lead and a large display that you can read easily from another couple of meters distance.
2) place the display where you can read it via CCTV, a daft waste of resources to install CCTV for this purpose, but worth considering if CCTV is already installed for security or other purposes.
3) If you don't need to know the exact temperature, but require warning of "too hot" or "too cold" then use a simple mechanical thermostat, a dry battery and a bell.
4) use a small telescope, or binoculars to observe an instrument that is too distant for direct sighting.
1) buy an instrument with a 2M lead and a large display that you can read easily from another couple of meters distance.
2) place the display where you can read it via CCTV, a daft waste of resources to install CCTV for this purpose, but worth considering if CCTV is already installed for security or other purposes.
3) If you don't need to know the exact temperature, but require warning of "too hot" or "too cold" then use a simple mechanical thermostat, a dry battery and a bell.
4) use a small telescope, or binoculars to observe an instrument that is too distant for direct sighting.
"Installers and owners of emergency diesels must assume that they will have to run for a week or more"
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Little John
A cheap alternative to standard CCTV is to use a second hand android mobile phone with an on-board camera and a free network video streaming app for the camera.
Something like this:
https://play.google.com/store/apps/deta ... pas.webcam
https://www.youtube.com/watch?v=Z6CH2CLEsTs
All of that assumes a high enough video resolution/appropriate focus capacity on the camera and/or a large enough display on the thermometer.
Something like this:
https://play.google.com/store/apps/deta ... pas.webcam
https://www.youtube.com/watch?v=Z6CH2CLEsTs
All of that assumes a high enough video resolution/appropriate focus capacity on the camera and/or a large enough display on the thermometer.