Regarding when to use thermistors and when to use thermal resistors
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There is a significant difference between temperature transmitters that use 4-20mA signals and thermal resistors that use PT100 signals; the cost difference for DCS cards is also substantial. For design institutes, how should they make choices during the design process? Are there any guidelines?
The current regulations do not provide any provisions.
The current regulations do not provide any provisions.
If the working environment on-site allows temperature variations within the range of -50 to 70 degrees, it is possible to use it there; however, in case the working conditions are harsh, it is better to use a card-type device to avoid failures caused by such conditions. I’ve also used both of the methods you mentioned, and the failure rate of the card components is significantly lower.
One advantage of temperature variation is that it can provide isolation, protecting the card components. For future maintenance and management, if I can use current signal cards to measure temperature. Then I can save a lot of costs. There’s no need to have too many different types of card inserts. If on-site temperature variation is not required, I can also use a temperature safety barrier to achieve the function of temperature variation. For ordinary thermal resistors, the error of thermocouples shall not exceed ±1.0°C. The accuracy of the D/A converter is ±0.025% of full scale, with good cold-end compensation; the overall temperature effect is ±0.1%/28°C. Therefore, in special operating conditions where high precision with regard to temperature is required, a temperature-compensated version must be used.
For on-site signals that need to be isolated or transmitted over long distances, thermistors should be used; for others, thermal resistors can be considered.
I am here to learn*. Our devices also have thermal resistors and thermocouples; I can’t tell the difference between them
The control circuit uses temperature sensing; an integrated or separate type can be chosen depending on the ambient temperature
1. If you don’t want different types of DCS card backups, temperature compensation can be used; however, the cost is not as low as mentioned above – on the contrary, it is higher. 2. The accuracy generally decreases when temperature compensation is used. 3. If there are few temperature points, it is recommended to use a temperature-sensitive element; if there are many points, either option is acceptable. 4. If lightning protection and isolation are considered necessary, use a temperature-sensitive element. 5. When using a temperature-sensitive element, make sure to choose one of good quality, otherwise you won’t even be aware of temperature drift. One thing to note: domestic temperature-sensitive elements tend to experience significant drift after a few years of use, which is far worse than using DCS temperature card terminals.
First, Party A requires that we normally opt for an integrated temperature sensor; for smaller factories, a Pt100 will suffice to meet the requirements. I recommend choosing an integrated temperature sensor