RTD Calibration

[NCENG78]

We exclusively use RTDs at our site for temperatures measurement. For 75% of the time we have an associated transmitter, but for our older facility we have RTD going straight back to the DCS IO Card. So for ISO reasons we have to calibrate each RTD each year. For the transmitters we simply shoot the loop to check integrity of the loop. For the RTD's that go straight back to the IO card we use a dry block to check calibration for each thermocouple. Obviously this is very time consuming. Is there any other way to check the proper function of RTDs without using a dry block?

 

[danw2]

So you won't think you've been ignored, I'll chime in and say that I'm unaware of any other means to calibrate an RTD other than to force it to a known temperature and compare its resistance with the standard table value.

Techs I know claim that oil baths are quicker to heat up a sensor than dry blocks because there's more heat capacity in the oil than in the relatively low mass aluminum block that most dry blocks use.

Dan

 

[cjw32]

If you're only checking the loop on the transmitters but you're using a dry block on the RTD's on the direct IO inputs then the tests are a bit inconsistent as you're only actually testing the sensing element with the dry blocks. All the transmitter test is doing is checking the 4-20mA from the amplifier. I'm guessing you're just injecting a 4-20mA signal into the loop to test the loop or are you using a decade box into the transmitter demonstrate that the transmitter is able to generate the correct 4-20mA?

If that's acceptable for the transmitter then why not just use a decade box for the other RTD's with the direct input?

Also I'm not sure what you mean when you say that you're using the dry block to test the thermocouple when you said that you only have RTD's.

 

[NCENG78]

Sorry I meant RTD