J-type thermocouple for temperature measurement
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As shown in the figure, a J-type thermocouple is used to measure the temperature of the equipment; the equipment itself is insulated. The height of the dashed box is approximately 500 millimeters, and the circular area at the top of the dashed box serves as a junction box for installing the transmitter. My question is: in the case of the dashed box area, whether insulation is present or not, what happens to the thermocouple itself? That is, when measuring the thermocouple alone, without the transmitter involved, the electromotive force generated, or the potential difference, or the mV value – I’m not exactly sure what to call it – but in any case, is this value the same in both situations?
If the shaded area is insulated, the temperature inside the junction box will be higher than when it is not insulated. This means that the temperature difference – the difference between the temperature at the thermocouple’s sensing point and the temperature at its terminal inside the junction box – will be smaller compared to the case where the shaded area is not insulated. As a result, the value of the thermoelectric potential MV will also be smaller. Also, the junction box should be as close to room temperature as possible. A high temperature in the junction box poses a safety risk… Could it not even cause those guy working with the instruments to suffer burns and become disabled?! :lol What if he turns around suddenly and his pants get burned, damaging the equipment as well? How would that be okay? Thinking about it this way, using the dashed area for insulation is absolutely absurd; it’s like some evil enemy trying to cause damage.....
Do you mean that, after insulation, the reading of the thermocouple wires inside the junction box will be higher when measured separately, compared to when there is no insulation? Is it possible then that it won’t increase, and will remain unchanged? Also, if the value of the thermocouple leads inside the measurement junction box is elevated, then the ambient temperature of the transmitter is also elevated; this shouldn’t affect the transmitter’s ability to perform cold-end compensation, right? I must be misunderstanding the concept of cold-end compensation
My final question is: why, after insulation, there is no change in the temperature inside the equipment, but the temperature output by the transmitter decreases? I want to confirm whether it’s a transmitter issue or a thermocouple issue
Heat retention → reduced temperature difference → decreased voltage output of the thermocouple in mV → if the temperature compensation in the signal reception circuit is not based on the temperature inside the junction box, then the temperature measurement result will be low!
The low measured value is caused by an incorrect selection of the thermocouple compensation point, that is, an incorrect potential reference point. . . Going a step further, compensating for the local temperature and processing the amplified thermocouple signals on-site is the proper way to achieve accurate temperature measurement.
One more thing to add: low measurement values are caused not only by inappropriate selection of points for warming therapy, but also by the technical methods and approaches used in such therapy, which often represent significant sources of error when it comes to accurate temperature measurement..... . .
Just talking about thermocouples alone. Without compensation, the measured millivolt value is correlated with the temperature difference. It becomes temperature-dependent only after compensation ； When the temperature inside the container is higher than that at the connection points, the higher the temperature at those connection points, the lower the measured millivolt value ； The lower the temperature at the connection point, the higher the measured millivolt value. Temperature compensation refers to eliminating the above two effects.
If there is a transmitter at XX that has built-in compensation, then the impact is minimal; otherwise, I can’t understand why insulation is needed at that dotted area A place with extreme cold?
The ambient temperature isn’t particularly low either, in the northeast. The problem now is that, after insulation, the temperature value output by the temperature transmitter with cold-end compensation has decreased significantly. I can’t understand why this is the case
You don’t understand what thermoelectric voltage refers to, nor do you understand what temperature compensation is. You need to know that the value output by the transmitter depends only on the difference between the ambient temperature of the transmitter and the temperature of the medium. The greater this temperature difference, the higher the output value. If no insulation is used, the temperature difference will be large; with insulation in place, it will be small. This isn’t that important, as temperature compensation is applied when the data is displayed in the control room. This compensation accounts for the difference between the ambient temperature of the transmitter and zero degrees, so what is displayed is the difference between the temperature of the medium and zero degrees, which is essentially the temperature of the medium itself.