selecting a temperature sensor for air/solvent vapor
selecting a temperature sensor for air/solvent vapor
(OP)
hello,
I need to select a temperature sensor for an air flow containing solvent vapours. My criteria are
- fast response. This is top priority
- fair accuracy and repeatability. I would choose a 3-wire pt100 if it had a faster response
- good chemical resistance. I would prefer an exposed sensor but any polymer such as thin film or pvc covered wire will be attacked by the solvent vapors
- should withstand a significant airflow, around 300 m3 /h (88 L/sec)in a 2" pipe.
the relevant temperature range is -10C to + 45 C.
Any ideas?
Claus
I need to select a temperature sensor for an air flow containing solvent vapours. My criteria are
- fast response. This is top priority
- fair accuracy and repeatability. I would choose a 3-wire pt100 if it had a faster response
- good chemical resistance. I would prefer an exposed sensor but any polymer such as thin film or pvc covered wire will be attacked by the solvent vapors
- should withstand a significant airflow, around 300 m3 /h (88 L/sec)in a 2" pipe.
the relevant temperature range is -10C to + 45 C.
Any ideas?
Claus





RE: selecting a temperature sensor for air/solvent vapor
xnuke
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RE: selecting a temperature sensor for air/solvent vapor
https://www.emerson.com/en-us/catalog/automation-s...
https://www.emerson.com/en-us/catalog/automation-s...
or this, but be careful of velocity and strength of element casing
https://www.emerson.com/en-us/catalog/automation-s...
Possibly with a Rosemount 1097 Thermowell (thin wall, 3mm)
Consider using 4wire pt100
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RE: selecting a temperature sensor for air/solvent vapor
Yes, I was a little vague there, i'll try to be more specicif.
response time
I have found a fast response RTD with a time constant of 2 sec. @ 63.2% and with a 2" inserted length and in stainless steel for direct immersion.
I think this would work but the 2 seconds are measured in moving water, and I don't know what to expect when the sensor is used for air instead. I suppose the response will be slower but by how much? I asked a supplier and they couldnt provide any useful info.
Accuracy / repeatability
Both thermocouples and RTDs would be Ok for this application. I have not used thermistors, they are said to drift over time and to self heat. They are not my first choice unless one of you convinces me otherwise.
chemical resistance
a thermocouple could give me the response time I need but I think they would be exposed elements or quite thin, sheathed elements and I doubt they are the right choice for the aggressive environment and/or the air flow.
I Can't used copper tipped probes either. The ideal materials are stainless steel and/or ptfe.
I was hoping that someone could see some options that I don't know about.
Thanks for helping
RE: selecting a temperature sensor for air/solvent vapor
RE: selecting a temperature sensor for air/solvent vapor
I don't think it will make a difference what type of element you use but RTD will be more accurate for sure. The velocity will be beneficial in reducing the time constant.
RE: selecting a temperature sensor for air/solvent vapor
RE: selecting a temperature sensor for air/solvent vapor
You can go without a Thermowell for faster response, but just remember if you ever need to replace the element, you will have to shut down your process!
______________________________________________________________________________
This is normally the space where people post something insightful.
RE: selecting a temperature sensor for air/solvent vapor
Roydm, good point about the volocity, I had so far only seen the problems which are that the velocity will make a very thin element vibrate until it fails. But indeed, the sensor may respond almost as fast as in water.
Thanks !
RE: selecting a temperature sensor for air/solvent vapor
RTD's require electrical current pumped through them in order to take a measurement so commercial RTD's are not grounded to the sheath.