How are the low and high limits, as well as the high-high and low-low alarm values for process parameters set? Are there any relevant specifications?
Thread Content
Background: Recently, there was an issue with one of the machines in our workshop, as many process parameters reached their alarm levels. After consulting with the workshop supervisors, the adjustments they made for HH/H/L/LL were based on experience (which I consider unreasonable). I searched the internet for information, but only suggestions from chemical industry professionals were available; I don’t quite understand it. Could someone please explain how the alarm values are set?
It depends on your process parameters; specifically, it depends on the process control range specified in your operating procedures
This indeed relies a lot on process stability or experience to determine.
I’ve always thought that we, as the owners, only have the operating parameters; this alarm value is provided by the design institute. Since they haven’t operated the system themselves, they lack experience, right? Am I wrong in thinking this?
Besides, I always feel that this experience or process stability is just something decided arbitrarily, with no basis at all :(
There are indeed such reasons… Some control parameters are interrelated, and it’s very likely that various factors affect them all… This makes it difficult to determine the exact values. However, setting upper and lower alarm limits should serve as boundaries beyond which losses or damages may occur; careful consideration is advised. If necessary, consult the design institute again or seek the opinions of several experts
We determine this based on the experience of our production process specialists; the design institute cannot provide such information, as their capabilities are not yet at that level. The data from historical records often deviates significantly from reality
After some internal deliberation, I also want to know what aspects experts consider important when deciding whether such an alarm should be set up; I plan to try and establish those criteria.
Bravo! Generally, the alarm values are determined by the process design team; in some cases, standards can be referred to. Part of it is based on methodology and empirical values.
This post was last edited by Military Emblem 81 on 2019-7-2 at 18:43. These values are usually set by process engineers (who determine them based on experience gained from the long-term operation of the process), and it is the instrument technicians who carry out the setting. If the set values need to be modified in the future, generally we must obtain written confirmation, signature, and stamp from the process engineers before making any changes, in order to avoid unnecessary problems down the road.
In my opinion, the setting of the alarm value should take into account the size of the storage tank as well as the flow rates of material inflow and outflow.