Thermocouple single point calibration
Thermocouple single point calibration
(OP)
Some people at work are suggesting the use of single point calibration in-place to calibrate our thermocouples/RTDs, and prevent damaging them through removal. Others are saying that this isn't effective because it doesn't give you at least one other point to set 0-point and span. Does anyone know where I can find literature on this subject so I can make informed suggestions. Thank you very much for any help





RE: Thermocouple single point calibration
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Thermocouple single point calibration
Two point verses one point determinations depend on the process you are controlling and the temperatures involved. With rather few exceptions most applications require control in a very narrow temperature range. Typically a process only needs one temperature. All others are only visited on warm-up or cool-down. Even the worst TCs will perform well if you calibrate them at or near the required operating-point-of-interest. In fact junk equations even work well in small temperature ranges.
So unless your process needs more than about a 100 degree range of full accuracy,(very few do), one point is certainly more than adequate.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Thermocouple single point calibration
Who in the world is still using thermocouples? Pt100s are state-of-the-art.
Regards
Wolf
www.hydropower-consult.com
RE: Thermocouple single point calibration
As to the OP question, I agree with Warcross, you cannot calibrate a thermocouple per se, it is what it is.
RE: Thermocouple single point calibration
Our dumb diesel and gas engines use thermocouples in the exhaust systems, and frequently in the engine temperature monitoring circuits as well.
I agree, technically you can't calibrate a TC, however, I firmly believe some effort should be made to perform a loop check verification if the TC is used for a critical process, like controlling a process where an overheat could lead to equipment damage or harm to people.
When I did lots of large engine commissioning, the TC circuits had the greatest number of problems, connection issues, cold junctions, reversed polarity, wiring damage, and wrong type installed or selected for the reading device.
Your check should assure the desired temperature measuring range is as accurate as you need, is linear and has the correct hysterisis, if it's important. If not, plug it in and go, reads close you're good, at least until something goes wrong and the AHJ asks how you verified it's proper operation.
Hope that helps,
Mike L.
RE: Thermocouple single point calibration
Application of TCs for gas turbines makes sense, of course. I narrowmindedly was thinking of electrical machines only.
Regards
Wolf
www.hydropower-consult.com
RE: Thermocouple single point calibration
RE: Thermocouple single point calibration
RE: Thermocouple single point calibration
Muthu
www.edison.co.in
RE: Thermocouple single point calibration
A single point check may not detect maintenance errors such as a TC replaced with the wrong type or the Xmitter set to the wrong type and the calibration in both cases adjusted at the normal operating temperature.
Two point calibration may also catch wrong type extension leads.
It depends on the reason for the calibration test, the possibility of maintenance mistakes and the overall company culture.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Thermocouple single point calibration
RE: Thermocouple single point calibration
RE: Thermocouple single point calibration
RE: Thermocouple single point calibration
Three questions:
Why do you want your TCs calibrated in the first place? What is the accuracy you require? What is the temperature range you have in mind?
Regards
Wolf
www.hydropower-consult.com
RE: Thermocouple single point calibration
It appears that a single point check of the thermocouple and a two-point calibration of the associated instrumentation would be satisfactory for most equipment; and perhaps pull the thermocouple and perform a two-point check and five-point instrument calibration for more process critical applications or for instruments with large temp ranges. We have more knowledgeable people on-site whose job it is to standardize these procedures, I just wanted to be able to give some feedback that might be of value.
RE: Thermocouple single point calibration