3 ms·

Out of interest what pt100 probe did you use? Would this be a 4 wire pt100? Also did you use a specialised chip for converting to digital readings? I vaguely

Out of interest what pt100 probe did you use? Would this be a 4 wire pt100? Also did you use a specialised chip for converting to digital readings? I vaguely recall looking at some fancy reference RTD thermometers with glass housings (just found them, they seem to be called SPRTs - https://isotech.co.uk/products/isotech-model-670/ https://isotech.co.uk/products/isotech-model-670/)

twawaaay 4y ago
I don't remember the exact PT100 I used but it wasn't very expensive (still probably one of the more expensive things I ever bought per unit of mass -- they are probably more expensive that diamonds). It was definitely 4 wire (you don't want to measure wire resistance change and 4 wire is only way to get rid of it). As to housing and type of RTD, a lot of the cost here is spent on making sure the measurements are stable over long time (so for example to prevent humidity and other gasses from putting it out of calibration). In my case I did not care a lot about it because I wasn't after absolute precision, for me the important part was rate of change. If you are after absolute precision you might want one of the fancy RTDs. But I cared that it is small and that it has very low thermal impedance interface with the measured object. Smaller means less thermal mass means faster response. For the chip I used a general purpose ADC. You also need a very good voltage reference, otherwise even best ADC isn't worth much.
- ISL 4y ago
  If you're primarily chasing sensitivity, one can generally be much more sensitive with a non-platinum thermistor. They're less stable but exhibit a much greater change in resistance with temperature. A good voltage reference (or current source) is important, but even more important is building up a reliable bridge topology.
  - deleted 4y ago
    [deleted]
  - twawaaay 4y ago
    You might be right about PTCs though I now can't remember exact reason for choosing PT100. It probably wasn't just linearity. I think I had other problems like controlling amount of power dissipated on the sensor (large changes in resistance mean large changes in amount of power dissipated) and possibly other.

twawaaay 4y ago

I don't remember the exact PT100 I used but it wasn't very expensive (still probably one of the more expensive things I ever bought per unit of mass -- they are probably more expensive that diamonds). It was definitely 4 wire (you don't want to measure wire resistance change and 4 wire is only way to get rid of it). As to housing and type of RTD, a lot of the cost here is spent on making sure the measurements are stable over long time (so for example to prevent humidity and other gasses from putting it out of calibration). In my case I did not care a lot about it because I wasn't after absolute precision, for me the important part was rate of change. If you are after absolute precision you might want one of the fancy RTDs. But I cared that it is small and that it has very low thermal impedance interface with the measured object. Smaller means less thermal mass means faster response. For the chip I used a general purpose ADC. You also need a very good voltage reference, otherwise even best ADC isn't worth much.

ISL 4y ago
If you're primarily chasing sensitivity, one can generally be much more sensitive with a non-platinum thermistor. They're less stable but exhibit a much greater change in resistance with temperature. A good voltage reference (or current source) is important, but even more important is building up a reliable bridge topology.
- deleted 4y ago
  [deleted]
- twawaaay 4y ago
  You might be right about PTCs though I now can't remember exact reason for choosing PT100. It probably wasn't just linearity. I think I had other problems like controlling amount of power dissipated on the sensor (large changes in resistance mean large changes in amount of power dissipated) and possibly other.