Relationship between interlock values and alarm values
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Is there a functional relationship between the interlock value and the alarm value?
It seems there is no universal functional formula to express the relationship between the two
The alarm value is always set a bit lower than the interlock value. As for exactly how much lower it should be, that is based on experience; one can adjust this value according to their own experience. Even the values provided by design firms are derived from accumulated experience, or from data suggested by those who operate the equipment.
Generally, the alarm value is closer to the normal value than the interlock value; the supplier of the process package will specify both the alarm value and the interlock value (if any), and there is no necessarily functional relationship between the two. Of course, in production operations, the set values can be adjusted appropriately based on accumulated experience, but modifications to the interlock values require special care; careful consideration must be given before making any changes.
Based on the process operation requirements, a 10-minute handling time is provided to the process operators between the alarm and the interlock action
Some instruments have alarms but no interlocks. Some instruments have both alarms and interlocks. It seems that there is no particular functional relationship between the alarm values and the interlock values; rather, they are more related to the experience of the designers and the requirements of the on-site equipment and processes.
There is no linear relationship. . . . It’s just that the alarm value has a narrower range than the interlock value range