There’s a small issue with the K-type thermocouple. . .
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K-type thermocouples (with stainless steel protective sleeves) are in use on site; the temperature measured there is 1014 degrees, and the millivolt value is around 40.1. When connected to the engineer’s station in the control room via a wiring board with fuses, the temperature reads only around 980 degrees. How can this be explained? . (The on-site temperature is provided by the heating wire; the control room determines whether to supply power based on this temperature value.) I would appreciate some advice from the experts out there.
The quality of the compensation wires used is generally poor; this is also related to the distance or to inadequate cold-end compensation
The temperature measured on-site is the same as that at the input terminal in the control room; however, there are deviations in the temperatures of both the input and output terminals of the cards in the control room. Could there be a problem somewhere along the way? . . .
With a deviation of 34°, it is first necessary to determine whether compensation is required and whether the extension cable is connected in the wrong direction.
First, it is necessary to clarify how measurements are taken on-site. When using thermocouples for measurement, cold-junction compensation is required, which makes it difficult to draw conclusions.
What control system is being used, and is it possible to directly monitor the millivolt value of the incoming circuit board? And how was the value 1014 obtained? Looking at Table 40.1, it should be around 960-970.
Through the safety barrier? Check whether there is a problem with the card, or determine whether it should be 0-5v or 1-5v in the DCS system settings
It mainly depends on whether the millivolt signal enters the system directly or after undergoing temperature conversion; if it goes through temperature conversion, it’s likely that no cold junction compensation has been applied. If the signal enters the system directly, you might consider trying another channel
First, determine whether shielded compensation wires are being used and what the transmission distance is; then choose between KX or KC compensation wires based on that distance； Furthermore, the temperature correction for DCS could be considered
40.1 is equivalent to 970 degrees