Instrument forced issue
Thread Content
I study engineering, and I’d like to understand when valve forced switching occurs, when DCS forced switching is used, when SIS forced switching is applied, and in what situations AI forced switching is employed, as well as when DI forced switching is used. I’m seeking help from experts!
It is determined by the process requirements. The instrumentation field merely serves to meet the requirements of the process.
AI is for analog forcing, DI is for digital forcing
What situations involve AI-driven enforcement, and what situations involve DI-driven enforcement? What does that mean?
AI forcing refers to manually assigning a value to an analog quantity; this is usually done because there are associated interlocks, and if there is a problem with the instruments on site, a value is assigned manually. As for DI forcing, this can be handled using an OR gate – an internal switch is connected in an OR relationship with the DI signal; whenever this internal switch is set to 1, the output will also be 1, which is equivalent to forcing the DI value to 1. Of course, such operations cannot be performed by ordinary people; only DCS engineers are able to do this
Based on the production process, the management has given approval.
DCS is a process control system primarily used for operating industrial processes, while SIS is a safety instrumented system used for interlocks. The forced operation of valves mentioned by the poster is primarily reflected in SIS. AI (analog input, i.e., various transmitter signals such as flow rate, pressure, temperature, level, etc.) and DI (digital input, i.e., various status signals such as pump operation signals, switch signals, valve position feedback signals, etc.) are all used as conditions for interlocks; the action of these interlocks is to open or close valves. Both AI and DI signals originate from field signals that enter the DCS and SIS, or from communication between the DCS and SIS. When the AI and DI signals from the field do not meet the required conditions, interlock mechanisms are activated, preventing the valves from being opened or closed. In such cases, if process operators want to open or close the valves, they must send a fake signal to override the interlock. There are several situations where forced action occurs: 1. The AI-driven forced action mentioned by the poster, as well as DI-driven forced action, that is, direct enforcement of interlock conditions. 2. Forced valve, that is, directly forcing DO to act on the valve, regardless of conditions. 3. The interlock has a bypass button
Based on the production process, the management has given approval.
I won’t tell you this; ask those in the instrumentation field.
In any case, it’s just signals for which forced interlocking cannot be activated. The others are different names for the same thing.