Is it necessary to use temperature (thermal resistor) for interlocking in the control of large-scale units?

In factories, large-scale units are generally referred to as the \"heart,\" which illustrates their importance. They are also extremely complex and costly, and interlock protection for such units is of vital significance. As for the necessity of temperature participating in interlocking, I think it is absolutely essential. As for the concern regarding the lag in temperature sensors, such as those measuring bearing temperatures, these sensors are usually built-in and armored, which gives them a faster response time compared to ordinary thermal resistors. Additionally, the set points for temperature interlocks in the unit are definitely set below the temperatures at which accidents could occur, in order to ensure a safety margin; this consideration is also aimed at addressing the issue of temperature lag. Moreover, any increase or decrease in temperature requires a process of energy accumulation, and theoretically no sudden changes occur during this process. Through qualitative analysis, it is clear that temperature protection in the unit is necessary. Whether this temperature parameter should be used for interlocks is not a decision that falls within the scope of the instrumentation specialists

Let’s talk about situations I’ve encountered personally. From the perspective of protecting the machine, the supplier of the unit makes it such that the shaft temperature HH is involved in the interlock shutdown mechanism; whether the shutdown is initiated manually or automatically, the requirement for a shutdown will not be compromised. Overheating means damage to the babbitt of the shaft bearings; it’s a serious accident. Although two redundant temperature probes are installed at one measurement point, generally only one of them is connected to the system for interlock purposes; thus, a failure of one of the probes that leads to incorrect shutdowns (due to instrument-related issues) will certainly cause dissatisfaction and complaints on the part of the production facility. If there’s a second accidental stop, the user will consider disabling the interlock. From a traditional perspective, thermocouples are more reliable in terms of resistance to vibration compared to thermal resistors; although this results in a slight loss of precision, it is still a worthwhile choice from the standpoint of operation and maintenance. When the shaft temperature drops to 105 degrees, displacement and vibration already become abnormal by the time it reaches 95 degrees (the shaft is out of alignment, and there is no lubricant to provide isolation between the shaft and the bearings). The setting for shutting down the system should have an accuracy of within 2 degrees, right? Currently, most units come equipped with thermoresistors embedded in the structure, and this actually imposes fairly high requirements in terms of manufacturing, installation, and maintenance (as you mentioned earlier). I work in a more traditional environment where thermocouples are still used, and things are working fine; an alarm is triggered when the connection to the thermocouple is lost (but the operation doesn’t stop). In the 1980s, three large ethylene plants were introduced in the country; the compressors from Mitsubishi, as well as the thermocouple temperatures, were not used to trigger shutdowns. Now temperatures require vehicles to be stopped in all cases – is it due to higher safety standards? I don’t understand; is it that the manufacturer has no confidence in the machines?