Questions about thermocouples?
Thread Content
This is the first time I’ve used a thermocouple in my work, a K-type one. I have some questions for fellow professionals: 1. Is the mV signal output by the thermocouple DC or AC? 2. At a room temperature of 20°C, using a multimeter to measure the two leads of the thermocouple shows 0 mV. Is this measurement method correct? According to the table, for a K-type scale at 20°C, the voltage output should be 0.798 mV; why is it 0 mV? Thank you all! :)
Let me make it clear right from the start: I’m no hero, as your questions are too simple. I’ll answer them one by one: 1. Is the mV signal generated by the thermocouple a DC or AC signal? Answer: DC voltage signal 2. At a room temperature of 20°C, when using a multimeter to measure the two leads of the thermocouple, the reading is 0 mV. Is this measurement method correct? According to the table, for a K-type scale at 20°C, the voltage output should be 0.798 mV; why is it 0 mV? Analysis: 1. Have you selected the correct setting on your multimeter? Is a multimeter good? 2. Is K-even good? If both are true, there must be a millivolt value.
Thank you, I’m wondering the same thing Let me confirm again
First, it is necessary to understand the principle of temperature measurement using thermocouples, as well as what is meant by the cold junction and the hot junction. If you hold the thermocouple at a room temperature of 20°C, with both the cold and hot ends at 20°C, how can there be any voltage if there is no temperature difference? Some people ask whether the multimeter settings are correct or if the thermocouple is in good condition; it seems really ridiculous
The first question was answered correctly! For the second one, please refer to the answer on floor 5!
1. The signal from a thermocouple is DC in the form of mV; I’ve never heard of instrument signals being AC. 2. If the thermocouple is placed indoors where there is no temperature difference, its output will definitely be 0!
This post was last edited by keviniwg on 2017-4-25 at 11:01. Thank you for acknowledging my answers; however, regarding the answer to the second question, I would like to emphasize once again and make a correction: even in the absence of wiring at room temperature, thermocouples can still measure electromotive force, it’s just that the temperature of the cold end is not 0°C, and there is a room-temperature error in the measurement results. Please be aware of this. Thank you.
This post was last edited by keviniwg on 2017-4-25 at 11:08. Thermocouples also generate an electromotive force at room temperature; it’s just that there is no compensation, which results in errors in the measurement values. Please don’t speak recklessly, and certainly don’t make fun of others.
This post was last edited by hfrs on 2017-4-25 at 11:16. It’s understandable that one might make mistakes with this issue before. So it is necessary to find out what the millivolt value of a 0-degree K-type thermocouple is, as well as what the resistance of a PT100 is. But the original poster is really clueless.