The issue of delayed instrument readings
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I have a question for everyone. I have very high requirements regarding temperature control here; in particular, it’s necessary to be able to respond quickly to changes in actual temperature. We use PT100 thermistors for temperature measurement, and the readings are accurate. However, due to the fast rate of temperature increase, there is a significant delay in the temperature displayed on the gauge. When the temperature reaches 60 degrees, the heating stops, but the gauge doesn’t react immediately – it may take a minute before the actual temperature of around 70 degrees is shown. The temperature range we need is 0–150 degrees, and logically, thermistors shouldn’t exhibit such a delay in temperature readings. Does anyone know what could be causing this delay in temperature readings here? Thank you in advance
I think it takes time for the temperature to rise, which is different from the sampling time you showed
Thermocouple thermal resistors have a time constant; check out the relevant information on this topic! We have encountered this situation as well.
The resistance value of a thermistor changes in a roughly linear manner as the temperature changes; therefore, the thermistor itself does not exhibit (or exhibits very little) lag. Since the temperature sensing element needs to exchange heat sufficiently with the medium being measured, it takes some time to reach thermal equilibrium; as a result, there is a delay in temperature measurement. A proper installation method and ideal temperature measurement points can be used to improve heat conduction and thus enhance the temperature response speed. Non-contact temperature measurement instruments (such as infrared devices) can also be used; they measure temperature based on the principle of thermal radiation, and the sensing element does not need to come into contact with the medium being measured. The response time is generally fast ； However, it suffers from significant measurement errors due to external factors such as the emissivity of the object, the measurement distance, as well as smoke, dust, and water vapor. This post was last edited by zhx7540 on 2007-12-29 14:11]
1\ If there are no major issues with the thermal resistors, the problem lies mainly in the improper installation or location of the sensing points. 2\ System-related problems: Some systems have issues with their processing capabilities; the scanning time is incorrect (this could also be due to problems with the host computer, resulting in an incorrect scanning time), and the quality of the system itself is poor.
Temperature transfer lag is a type of pure lag that cannot be overcome; it can only be compensated for through certain measures. Check whether the insertion depth of your measurement point is sufficient ； Is it installed in a representative location? ； Replacing the armored thermoresistor can improve the response speed slightly ； Some secondary meters (IO components) also have a rate of change setting, similar to damping; look for it and make the changes.
I agree with Han Xing’s view... If you really need a very fast response time... you could consider using infrared technology...
It’s not a measurement issue; adjust the controller, and you can reduce the overshoot!
Using a fast thermocouple, with a response time in the millisecond range.
It’s possible that the thermometer wasn’t inserted deep enough, resulting in inaccurate readings.
The main reason is the lag of the temperature sensing element. I solved the problem by using a film-type PT100 element (slightly larger than a sesame seed) that I made myself. It’s mainly a packaging issue: the PT100 element is enclosed inside a thin-walled stainless steel capillary, and thermal conductive silicone grease is injected into it, with the amount of grease being sufficient to cover the element. If the pressure is high, my method won’t work.