Thermal resistance issue
Thread Content
The resistance value is very stable at room temperature, which is no problem. However, once the resistor core is inserted into the device, the resistance value changes by about 0.3Ω. This change isn’t observed at room temperature on the device; it’s a new resistor core. What could cause such a change in the resistance value? I measured the thermistor directly; all the wires weren’t connected. That’s exactly why it was replaced before, and I didn’t expect the same problem to arise even after the replacement
The resistance value of a thermistor is affected by the ambient temperature; as the temperature rises, the resistance value increases； As the temperature decreases, the resistance value decreases. Therefore, when measuring a thermal resistor, it is necessary to ensure that the temperature remains stable; only by conducting the measurement under such conditions can accurate results be obtained. If the resistance value changes after a new resistor core is inserted into the device, it may be caused by the following reasons: 1. Unstable temperature: Changes in the temperature around the device lead to variations in the resistance value output by the thermistor. 2. Wiring issues: There may be problems with the wiring, such as poor connections or inadequate contact, which can lead to inaccurate measurement results. 3. Issues with thermal resistance elements: The new resistance elements themselves may have problems, such as poor quality or damage, which leads to inaccurate measurement results. It is recommended that you check whether the device configuration and wiring are correct, ensure that the ambient temperature remains stable during measurement, and also try using multiple thermistors for testing in order to determine if there are any quality issues with the thermistors themselves. .
Regarding the fault symptoms you’re experiencing, I personally think there are slight fluctuations in temperature
. The situation in question appears to be affected by electromagnetic interference. When measuring the resistance value on-site with the subsequent circuits completely disconnected, if there are fluctuations in the resistance value, one of the wires of the thermistor can be directly connected to the metal cover (protective tube, armored shell), and then the resistance between the two wires can be measured. If the fluctuations disappear, it can be basically determined that the fluctuations were caused by interference. .
I had one wire that wasn’t disconnected; once everything was disconnected, things stabilized. For some cases, it worked fine as long as only point A was disconnected – what’s the reason for that?
. From personal experience, it is necessary to prioritize eliminating interference issues. Disconnect all connections at both ends of the signal cable, and check the insulation of the cable ； Check the shielding of the signal cable; the shielding layer must have only one grounding point. If shielded wires are not used, it is necessary to ensure that the wires are placed inside metal conduits and trunking ； The protective sleeve of the thermal resistor must be grounded (no special connection is required except in the case of electric furnaces, but it must still be connected to ground) ； There should be no electrical connection between the shielding layer of the shielded cable and the measurement protection tube ； If negative grounding is used for the DC power supply of the instruments, it should be connected to the same grounding system as the shielding grounding in the control room ……