Regarding the issue of whether to initiate interlock or alarm first on DCS
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The workshop supervisor in our plant said that for some monitoring parameters on the DCS, the original setting was such that the interlock value was lower than the alarm value; as someone who works in system design, I consider this unreasonable. But they want me to find the specifications. May I ask the experts, has anyone seen it specified in any standard?
It depends on what kind of interlock it is; there is no requirement that the interlock value must be lower than the alarm value. For example, the use of a pump to add water based on liquid level interlocks – although it is called an interlock, it is actually a form of process control. An alarm is issued only when adding water fails to raise the liquid level and it continues to drop.
Is this parameter a low-level alarm/low-level interlock? … p: (Alarm when pressure is below 1, interlock when it is below 0.5)
In the case of safety interlocks, such as those related to tank liquid levels, an alarm is given first before the interlock is activated. For operational purposes, such as automatic loading and unloading in metering tanks, the interlock is triggered first; if the liquid level continues to rise after the interlock is activated, then an alarm is issued
It depends on whether the interlock is low-low or high-high; this is determined by the production process
The process engineering department makes the decisions, while the automation and instrumentation department generally inputs the set parameters provided by the process engineering team. Generally, high and low values are set as alarm values, while extreme high and extreme low values are set as interlock values
The high and low levels are determined in accordance with the process requirements; for example, if the oil pressure is low, an alarm should be triggered first, and if it drops further, a interlock mechanism should be activated. If it is the compressor outlet pressure, an alarm should be set for high pressure first, and interlock should be activated at even higher pressures. The concept of high and low patterns cannot represent everything; it is for reference only.
The process is finalized; once the process is set, automatic control is implemented
Life is like tea 16 was published on 2022-2-17 at 16:39. In the case of safety interlocks, such as those related to tank liquid levels, an alarm is given first before the interlock is activated. For operational purposes, such as automatic loading and unloading in metering tanks, the interlock is triggered first… Agree
This can be explained using the HAZOP standard GB/T 35320-2017: when the set value deviates to the alarm value, this constitutes the operating range; the distance from the alarm value to the high-alarm interlock value represents the time available for human operation to respond. Once the high-alarm condition is reached, the system initiates its interlock response – that is the logic behind it.