How to achieve proper vehicle exit? Should we consider reducing accidental exits?
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A device is equipped with a two-point bearing temperature interlock; the system shuts down when the temperature exceeds 65 degrees Celsius. It is desired to reduce unnecessary shutdowns. Is it okay to have the vehicle not shut down in case of a fault in one temperature sensor (for example, if the cable connected to that sensor is broken or there is a short circuit), and only shut down when the temperature at the other sensor exceeds the limit? Or does it shut down every time a fault occurs? This post was last edited by zhaohh3211 on 2009-4-1 09:47.]
This is likely related to the manufacturing process, particularly mechanical considerations. If the temperature of the bearing shells rises slightly, it should prevent normal operation; however, if this does not cause damage over time, a dual-point alarm system can be set up to trigger interlocks, which can reduce the frequency of shutdowns. Or simply increase the chain alarm threshold. However, if it is possible to eliminate alarms for cable disconnection and short circuits, so that they do not participate in the vehicle shutdown interlock, that would be the best solution.
Some DCs have the capability to detect short circuits. You can give it a try during configuration.
Could a three-out-of-two interlock system be considered? With this approach, I want to ensure both the safety of the system and prevent it from stopping frequently; I want it to remain operational continuously. To that end, three detection elements can be used – three signals are received, and an interlock action is taken only when two of these signals reach the specified threshold value.
For example, a typical device has three temperature measurement points while it is in operation. If the normal operating temperature of such a device is 30 degrees Celsius, then if two of these three measurement points exceed 65 degrees Celsius, the device will shut down. There are various reasons that can lead to this shutdown: 1) the temperature of the device’s bearing pads exceeds 65 degrees Celsius; 2) more than two of the temperature sensors fail, which also results in shutdown. However, shutting down the device just because one sensor fails would be unnecessary. Therefore, to ensure the proper operation of the device, three temperature measurement points are usually used, and shutdown is triggered only when two of them exceed the set threshold. This essentially serves as a voting mechanism. This is typically achieved through interlocks. If the logic is inverse, where 0 represents normal operation and 1 indicates an alarm, then the logic follows what was explained on the fourth floor. But if it’s positive logic, where 1 represents normal operation and 0 indicates an alarm, then AND gates are used to implement the logical relationship. Do you understand now?
What was said upstairs is very comprehensive. Just adding more. In fact, for temperature design, thermocouples or thermal resistors are inserted at different locations and depths to select the temperature output. Then an AND operation is performed to output the trip signal. This also allows for diagnostic shutdown using two dots. However, it is necessary to be familiar with the pump body temperature structure and the properties of the process medium.
I agree with the views of those above. An alarm for the rate of temperature change can also be added. Temperature detection always has a response time, and changes occur continuously; if there is a sudden increase in the rate of change, it is considered a fault in the detection signal, and the faulty component is automatically disconnected from the interlock system. The interlock can only be reactivated manually after the issue has been resolved and everything is working properly. This approach helps to prevent incorrect operations caused by faults.