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Measuring Cryogenic Cooled Ethanol

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  • Measuring Cryogenic Cooled Ethanol

    I need to measure the temperature of Cryogenic Cooled Ethanol (Food Grade, 200 Proof) at -40C to -35C. It appears that the ProSense RTD1-S04-03 would be an ideal RTD sensor as it already meets the Sanitary requirements and temperature range.

    My question has to do with the hazardous environment. If the ethanol leaks, it is an explosive hazard. In another room, what kind of RTD/4-20mA Transmitter do I need? Are any of the ADC units suitable? Is this RTD probe even acceptable?


  • #2
    How far does the signal need to go? the currents and voltages on a RTD are so low that I suspect it could potentially be made intrinsically safe (that would depend on what is at the other end of the wire, but it would seem the potential is there) If you can just run RTD extension wire to outside the hazardous area it might be easier.
    Sure, converting to 4-20mA is better for long runs, but 20mA is at least an order of magnitude higher than what is needed to measure an RTD. However, 20mA is still not a whole heck of a lot and could meet the requirements of intrinsically safe anyway, I suppose one just need to have the power supply to the transmitter properly current limited.

    A quick look at ADC's online catalog seems to show that the lowest any of their transmitters go is -40F which means you be right at the bottom of their range, not the best place to be.
    Well, looking a bit deeper, it looks like the FC-R1 can read down to -200C, though it is a DIN rail mount (not gauge head mount) and the catalog says nothing about being hazardous area rated, so I suppose one would want to run RTD extension to outside the hazardous area. One might check with someplace like Omega.com, they do have some FM approved signal conditioners, but they are expensive (and I was not impressed but the performance of their web site)

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