Thermocouple input redundancy issue in DCS

The accuracy should be guaranteed; whether to include a safety barrier depends on your explosion protection requirements.

The precision should be sufficient; no problem! If it is in an explosion-proof area, a safety barrier must be added!

Accuracy is guaranteed; a safety barrier must be used when there is a 4-20mA input from a thermocouple and explosion protection is required

Generally, there are dedicated circuit boards with thermocouples, so no conversion is necessary. However, adding a transmitter is unlikely to affect accuracy after conversion; whether to include a safety barrier depends on the explosion protection rating. If the company has the money, just add it:lol

The precision of the DCS card should meet the requirements. If the instrument is located in an explosion-proof area, appropriate safety barriers must be installed. It is necessary to add redundancy at critical measurement points, although this increases the hardware investment cost.

We also achieve redundancy in the temperature control circuit in this way nowadays; however, we usually place the conversion function on-site, which also helps to save on the cost of compensation wires, which are much more expensive than ordinary cables. The accuracy should be fine.

For systems that rely on temperature zone control, it is generally required that the MV value be converted into a 4–20mA analog signal as a result of temperature-related adjustments. This signal is then fed into the DCS via redundant AI input cards. Such conversion does not compromise accuracy; on the contrary, it enhances stability (since the cards in the DCS that receive MV signals are usually not isolated for each channel, whereas those that receive 4–20mA analog signals are typically isolated for each channel). Additionally, the installation of temperature sensors has nothing to do with whether a safety barrier is needed; as long as there are explosion-proof requirements at the site, a safety barrier or isolation barrier must be installed. This post was last edited by harbin_999 on 2009-2-9 18:24.]

In this case, explosion-proof thermocouples do not require a safety barrier

Yes, it is very difficult to implement IO redundancy in the AI cards for TC signals, while it is almost impossible to do so for AI cards handling RTD signals – this is determined by the principles at the circuit level. It is recommended to use a signal transmitter to convert the signal to a standard 4-20mA format, and then employ a current-type AI card to achieve Io redundancy. If in a hazardous area. A temperature-type safety relay can be used: the input is TC, and it is converted to 4-20mA for output. The accuracy is guaranteed at present. In this way, it is both a temperature sensor and a safety barrier

Safety barriers must be installed in explosion-proof areas. The redundant design for thermocouple inputs involves placing two thermocouples in the same temperature area, so that the temperature can be measured simultaneously and safely using both thermocouples. If the temperatures measured by the two thermocouples exceed the set range, it is considered a fault, and an alarm signal is generated to trigger inspections and troubleshooting.

Regardless of the approach, redundancy varies; there is partial redundancy as well as full redundancy. So you need to check whether 1 the field thermocouples are redundant, 2 the wiring is redundant, 3 the input terminals are redundant, 4 the input modules are redundant, 5 the control modules are redundant, 6 the IO bus is redundant, and 7 the power bus is redundant. Generally, the level of redundancy is determined based on the importance of the measurement points. As for safety barriers, they are usually not used if compensation wires are used to connect them to the system; however, in some cases they are necessary (when the input modules have poor isolation and interference resistance capabilities), mainly to protect the module channels. If it is not connected to the control room using compensation wires, then the safety requirements at the site need to be taken into account; if those requirements are relatively high, a safety barrier should be used.

A temperature-sensitive safety barrier can be selected; it is converted to 4-20mA before redundancy is implemented