****It should be designed to be fail-safe； Field bus communication should not be used; assistance is requested as the situation is unclear

My understanding is that your signals are currently uploaded to the DCS or PLC via a fieldbus. He required that a logic loop signal should be connected via hardwiring to the same DCS or PLC station, and interlocking could not be achieved through fieldbuses. I’m not sure if my understanding is correct; this is for reference only.

My understanding is that devices for which safety interlocks cannot be ensured through fieldbus communication are such devices. According to the meaning of the first sentence, there is a one-to-one signal transmission from the sensor to the system or instrument, and from the system or instrument to the actuator; bus communication cannot be used

Final actuating components such as valves cannot use direct bus control types; instead, traditional fail-safe types must be used.

The communication between the instrument and the actuator is a one-to-one signal transmission; bus communication cannot be used

The so-called \"fail-safe\" concept means being in a safe state in the event of a failure. Consider a pressure control valve used to regulate the pressure of a certain device: it opens more when the pressure is high and closes slightly to maintain pressure when it is low. If the pressure in this device becomes too high, an explosion can occur; however, low pressure does not pose any danger. In such cases, the pressure control valve must be designed to remain in the fully open position in the event of a signal failure – this is what fail-safe design entails.

　　Fail-safe means automatically entering a safe state in the event of a failure. For control devices, this means that if the device malfunctions and can no longer function properly, it should automatically enter a safe (or interlocked) state. A common specific application is the selection of air-open/air-close for control valves and normally open/normally closed for limit switches. There are many discussions on forums regarding such issues; you can search for them by yourself, for example: http://bbs.hcbbs.com/thread-51660-1-1.html and http://bbs.hcbbs.com/thread-1397235-1-1.html. A characteristic of fieldbus communication is that data transmission does not require adherence to any physical order – it doesn’t matter whether devices are connected in series or in parallel, as long as they are connected together. Especially when individual devices fail to respond, they are left unattended. The advantage of this approach is that the physical connection is simple, and the entire control system will not come to a stop due to problems with individual devices. But the problem is that it will cause critical data to become invalid. For example, three instruments using a two-out-of-three voting system can be connected together on-site via a bus connection, and then connected to the control room with a single cable. If the communication is fine, a two-out-of-three voting mechanism works normally, but if the communication is impaired, the entire control system becomes ineffective. Therefore, the specifications require that each gauge be connected to a different card in the control room (this connection can be via bus communication, but it does not have to be done in a bus-based manner). Only then can the main computer in the control room handle it as three separate measurement systems. 　

Fieldbuses are suitable for applications with moderate safety requirements; for critical applications, hardwired connections are still necessary