Selection of temperature sensing element?
Thread Content
Temperature measurement (temperature 150°C): Should a thermal resistor be used or an integrated temperature transmitter? Combination 1: Explosion-proof thermal resistor at the field site + RTD card in the control room. Combination 2: Intrinsically safe integrated temperature sensor at the field site + safety barrier in the control room + AI card in the control room. Combination 3: Explosion-proof thermal resistor at the field site + safety barrier in the control room (for converting resistive signals to standard signals) + AI card in the control room. Let’s analyze them from the perspectives of price and measurement accuracy. Also, I would like to ask whether all thermal resistors are flame-retardant? Is there still a intrinsically safe one? Or do thermal resistors not come in intrinsically safe or explosion-proof versions, and it is only when combined with a transmitter to form an integrated temperature sensor that intrinsically safe and explosion-proof versions become available? Please ask an expert to answer, thank you!
The accuracy of measurement using thermal resistors and integrated temperature sensors with built-in temperature sensing is roughly the same. In the case of thermal resistors, signal conversion takes place in the cards located in the control room, whereas with integrated temperature sensors that include thermal resistors, signal conversion is carried out on-site. As for the price, it’s hard to say; prices vary significantly among different brands.
I often use explosion-proof thermal resistors combined with PT100 input cards to configure such temperature circuits. Because integrated temperature sensing can cause errors in temperature measurement in the cold winter climates of the north. If an intrinsically safe circuit is to be used, a PT100 thermistor should be paired with an intrinsically safe temperature transmitter in the control room, and the signal should then be fed into a 4–20MA output module. It is important to use intrinsically safe cables in this circuit in order for it to function as an intrinsically safe circuit.
Thermistors are recommended for temperatures below 600 degrees; integrated thermometers are advised when the transmission distance is large. The choice between explosion-proof and intrinsically safe designs should be determined based on the local explosion protection requirements.
As for explosion protection, in a strict sense, it is divided into intrinsically safe and flameproof types. The personal analysis regarding the selection between thermal resistors and integrated temperature sensors is as follows: it should be clear that thermal resistors and thermocouples are chosen based on the different temperature ranges they can measure, and when a temperature sensing module is added, it is referred to as an integrated system. There is a limit to the transmission distance of thermistor signals, after all, they are resistance signals being transmitted. Increasing the module improves the accuracy and range after conversion to a standard signal; thermal resistance measurement involves only a small sensing element at the bottom. Therefore, I personally believe that there is no issue of high measurement errors in the northern environment. Considering the type of components used in the control system as a whole, if there are many thermoresistors and they are not very far apart from each other, it is possible to connect the thermoresistor signals directly. If the number of thermoresistors is not large, then it is advisable to use heating modules; this approach helps to reduce the number of components required in the control system as well as to improve the consistency of the cables used.