I would like to ask you some questions about thermocouples.
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I'm new to instrumentation. I saw a thermocouple today. I read it in the book but it said it was not very nutritious. I have a few questions to ask the seniors in the forum. Thank you. 1. I drew a simple diagram by hand. If I use a multimeter to measure the millivolt value at the junction box, is this value the output thermoelectric potential value of the working end of the thermocouple or the thermoelectric potential difference in the entire loop? Do I need to remove the wires when measuring the millivolt value? 2. If the millivolt value of the junction box is 1.5mv and the ambient temperature is 10 degrees, how can the temperature of the working end be determined? 3. If the installation location of the thermocouple is not convenient for me to measure, is it feasible for me to measure the millivolt value at the terminal of the secondary meter? What exactly is this millivolt value? 4. For the connection line between the junction box and the secondary meter, the cold end can be extended to a place with a constant temperature by using a compensation wire. However, if the temperature in this place is not 0 degrees, assuming the indoor constant temperature is 22 degrees, then how to eliminate the influence of this 22 degrees on the loop thermoelectric potential? What are the forms? 5. What will happen if I don’t use the compensation wire?
What are the forms? 1. It is the thermoelectric potential output by the thermocouple. This thermoelectric potential needs to form a loop to be meaningful. There are other signals in the loop, and the wiring needs to be disconnected for measurement. 2. If the millivolt value of the junction box is 1.5mv and the ambient temperature is 10 degrees, you need to add the mV value of the junction box temperature. How to look up the table to get the temperature of the thermocouple measurement end. 3. If the installation location of the thermocouple is not convenient for me to measure, is it feasible for me to measure the millivolt value at the terminal of the secondary meter? OK, just like the field, the use of the thermocouple compensation wire is equivalent to the extension of the thermocouple. 4. For the connection line between the junction box and the secondary meter, the cold end can be extended to a place with a constant temperature by using a compensation wire. However, if the temperature in this place is not 0 degrees, assuming the indoor constant temperature is 22 degrees, then how to eliminate the influence of this 22 degrees on the loop thermoelectric potential? Just use the display instrument with automatic cold end compensation. 5. What will happen if I don’t use the compensation wire? Inaccurate measurement
Thank you for your answer, :victory:
The answers on the second floor are very detailed, learn* Got it
Thermal resistors and thermocouples are just rogue if they are not equipped with temperature change modules. They require 3-core cables and compensation cables, and thermal resistors and thermocouple clamps are needed between cabinets. It is not possible to save much cost. The signals between cabinets are not uniform, making maintenance troublesome.