Rosemount temperature transmitters for measuring thermocouples
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In actual on-site installation, as in RT, the compensation wire runs from the primary sensing element of the thermocouple to the transmitter; it does not extend directly to a location within the cabinet where the temperature remains constant, as described in the textbooks. So how is temperature compensation at the cold end achieved? Seeking help from experts
The cold terminal is the transmitter; from the transmitter to the cabinet, a converted 4-20mA/1-5V standard signal is transmitted. Temperature transmitters come with their own models and compensation settings, and automatic cold terminal compensation can be achieved through a built-in bridge circuit
Bro, is the principle of the compensation circuit a bridge circuit? What is the principle behind the compensation of this circuit?
No problem. Modern temperature transmitters come with built-in temperature compensation, not to mention those from Romon
As a supplementary note, by converting it to 4-20mA, temperature changes are no longer a concern
The basic principle of thermocouple temperature compensation is to add a compensating potential to the thermoelectric potential of the thermocouple, based on the law of intermediate temperature for thermocouples. When the intermediate temperature remains constant, the compensation potential can be replaced by a fixed temperature reading ； When the intermediate temperature changes significantly, the temperature transmitter measures the intermediate temperature and generates a compensation potential ； The two methods for generating the compensation potential mentioned above can be used simultaneously. In a thermocouple circuit that uses compensation wires, the compensation wires and the thermocouple can be regarded as a single unit, treated as one thermocouple. It can eliminate a lot of confusion regarding compensation issues.
I have cropped a page from our training PPT; below is the principle of temperature compensation
This post was last edited by Sai Xin on 2022-2-11 at 17:01. The round-shaped temperature-sensitive modules that we usually see are supposed to be a single unit; the built-in temperature sensor inside (I assume it’s a PT100 element, with NTC elements being less common) should not be removable； I checked; for Romon’s models 248 and 644, the accuracy of this cold-end compensation is roughly 0.5°C ； Another one is from an imported brand; it’s 1.0°C – a value that appears on the samples provided by these temperature-sensitive manufacturers. I also spent some time studying this today
For temperature variation, there is a cold-end thermometer that allows for compensation on the transmitter side.