Can the alarm values and interlock values of DCS be the same? Is there any regulation that prohibits such consistency or permits it?
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If consistency cannot be achieved, for devices that must have multiple alarm settings, is it possible to set them as follows: ultra-high level interlock value, high-high alarm value, high alarm value, low alarm value, low-low alarm value, and ultra-low interlock value?
This alarm value is determined by taking into account factors such as your process requirements, the properties of the materials, and safety factors. There are no explicit regulations specifying how to set it, but alarm levels for high and low values, as well as the shutdown of material intake and output, are essential.
There are no clear regulations; personally, I believe they shouldn’t be the same value
The alarm serves to alert the operator visually and audibly; its value should be lower than the interlock control value； If the alarm value is equal to the interlock value, the alarm value loses its meaning. For example, in the case of level control for a storage tank containing a major hazard substance, the maximum filling factor is 0.85. The liquid level corresponding to this value of 0.85, as determined from the tank capacity chart, should serve as the interlock setpoint for the shut-off valve. Subsequently, based on the rate at which the liquid level rises due to pumped material, a response time of 5 to 10 minutes should be established for setting both the high-high level alarm and the high level alarm ； If the tank is an internal floating roof tank, per regulations, it is strictly prohibited for the floating roof to touch the bottom while the tank is in operation. In such cases, the low-limit interlock cut-off value should be set at a level slightly above that at which the floating roof touches the bottom. Similarly, low-level alarm and even lower-level alarm settings should be established.
Personally, I think the alarm value should be slightly higher or lower than the interlock value to serve as a warning.
How many conditions are needed just to keep the control room staff from worrying too much? If the alarm and interlock are set to be the same, what is the purpose of having an alarm? Does the law also stipulate this for you?
It depends on how many levels of alarm are set. The first-level alarm on the instrument serves as a reminder for the operator to take action, while the second level triggers an immediate interlock. If it’s at the same point, aren’t you worried about the device stopping frequently? Can production handle it?
Figuring out what the purpose of setting up alarms is, and what the purpose of interlocks is as well