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Temperature sensors have been widely used, but some engineers and technicians cannot skillfully design procurement standards or requirements during the design and selection process (this does not refer to the relevant technical parameters of the temperature transducer). They might blindly compare prices, or fail to consider the key factor. And at the end they might buy the wrong product, for example the final temperature transmitter purchased might be not cost-effective, or the low-priced products are not easy to use, or high-priced purchases are used in occasions with low use requirements. So, how to choose a suitable temperature transducer?
The accuracy of ordinary temperature sensors and temperature meters is mostly 0.2% FS, and the temperature sensors of general analog circuits belong to this category.
Temperature sensors with higher accuracy generally have an accuracy of 0.1% FS, which is a digital temperature transmitter or an intelligent temperature transmitter. This kind of temperature transducer has good stability, wide power supply voltage range (generally 9~30VDC), adjustable range (the smallest range difference can be 50℃), and the input resistance is generally any two, three, or four-wire PT100 option, according to customer requirements, which can also be connected to PT1000. Unlike the temperature sensor of the analog circuit, which can only be connected to the three-wire PT100, the lead wire resistance of the transmitter cannot be overcome when the transmission distance is slightly longer than tens of meters. It can only be corrected on the host computer, and the integrated temperature transducer itself the accuracy has not reached the technical parameters of 0.2% FS, and the minimum range difference is basically above 100 ℃.
Current secondary instruments generally require temperature sensors to output 4-20mADC current signals, and individual requirements are RS485 signals. Generally, acquisition cards have more voltage signals of 0-5VDC. The analog signal that PLC CPU directly accesses is generally 0~10VDC, rarely 4~20mA signal, and 4~20mA analog input module. 4-20mA analog input module, the general wiring method is three-wire, but when purchasing a temperature transmitter, two-wire 4-20mA is actually fine, as long as the PLC and the ground terminal of the temperature transducer are connected to the ground when wiring, some people are looking for a three-wire temperature transducer with 4-20mA signal all over the world, which is actually unnecessary.
This is a proposition that everyone has his own opinion. Products purchased at lower prices may only achieve a lower initial budget cost. Products purchased at higher prices may not have a high final cost. Of course, this includes a series of issues such as maintenance, after-sales and service. Therefore, please consider the cost performance, not just the price.