Regarding the issue of temperature drop in digital display instruments with compensation wires
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There is a digital display currently available, set for an S-type thermocouple. Inside, connect the S pair with a section of S-shaped compensation wire. The temperature displays the room temperature, and after a while it gradually drops to 10°C. After replacing the compensation wire with a regular wire, the measurement was taken at room temperature. Suspect a problem with the compensation wire. By directly short-circuiting the compensation wire and connecting it to the digital display, the reading dropped from over 40 degrees to 10°C. Pressing the contact with the hand raises the temperature, while releasing it lowers it. When connected in reverse on the digital display unit, the temperature reads over 40 degrees; pressing the contact causes the temperature to drop, while releasing it causes the temperature to rise. Currently, the compensation wire is being connected to the DCS card for observation. Let’s discuss it together. The room temperature is around 25°C.
Based on the description, it seems to be a problem with the compensation wire. Since digital display instruments all have an automatic cold-end compensation function, the display showing room temperature after replacing it with a regular wire indicates that there is nothing wrong with the display instrument; try using a new compensation wire.
If the digital display shows a low value, it is likely due to a negative millivolt signal; there can be no negative millivolt signal if there is no temperature difference at room temperature, so the issue lies with the compensation wires. Even if the model of the compensation wire is selected incorrectly, the room temperature shouldn’t be low. And how to explain his gradual decrease step by step?
The value connected to DCS is also low, but by only a small amount – 22°C. Now I suspect that the temperature sensing probe of the digital display instrument is located on the circuit board; as the power supply continues, the temperature rises there, while there is hardly any temperature difference at the connection terminals of the digital display instrument and the thermocouple. Is this gradual decrease in temperature the process of the circuit board’s temperature rising?