I have a question: what does \"take the higher of the two high level limits\" mean?
Thread Content
I have a question: what does \"take the higher of the two high level limits\" mean?
This is a type of interlock: when one of the two detection points detects that the liquid level has reached the high-high limit, an alarm is triggered or interlock protection is activated.
A dual protection mechanism is provided for critical areas or process parameters to prevent instrument failure; two instruments are installed, and when one of them reaches the high-high limit, a interlock system is activated.
Control components generally have an average fault-free operating time of around 20,000 hours. To prevent adverse effects on production, measures such as two-out-of-one, three-out-of-two, and five-out-of-three voting systems can be employed. Depending on the level of hazard associated with the device or the requirements of the process, there is generally a maximum allowable failure probability, such as 1/10000, 1/100000, or 1/1000000. Through calculations, it can be determined which of the options—one out of one, two out of one, three out of two, or five out of three—is the most suitable.
Simply put, it is to prevent a false alarm interlock
Preventing false alarms should involve a two-out-of-two system; a two-out-of-one system serves to increase the safety level, with interlock activation upon one alarm.
There are two monitoring points; when one of them reaches the preset parameters, an alarm is triggered or an interlock action is initiated. This is done mainly to prevent instrument failures. Of course, this can also lead to false alarms, and it is necessary to take into account the level of risk associated with the process as well as the reliability of the instruments. If the risk is high, then the reliability should be increased, by using a configuration of three out of two or even higher