What is the basis for setting a signal delay on the emergency stop button in safety interlocks?
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Recently, the signal for the on-site emergency stop button of the plant’s safety interlock system disappeared suddenly, resulting in an interlocked shutdown. It is a malfunction. To reduce malfunctions, the device proposes the use of interlock delays. I think that if a delay is set, adding two or three seconds of delay doesn’t help in solving the problem at all; the operator simply won’t be able to react within those two or three seconds. It increases the possibility of interlock failure. Yet no basis or **standard can be found to reject it. Do the experts have any good suggestions?
More contact pairs, additional criteria for detection of broken wires
Your question falls under the category of investigating accident causes, and no delays in making changes are allowed. From the perspective of the procedures for making changes, it is necessary for the relevant equipment department to take the lead, work with the design manufacturer, and obtain approval from the production manager before such changes can be carried out; there is no need for you to look for relevant documentation. Actually, the basis is the original equipment manual. From a technical perspective, there are two possible explanations for this phenomenon: one is that it was indeed considered to have been tampered with, and what is the other possibility? ? ? If it’s truly a malfunction, then it’s necessary to find out what caused it – was it a relay or the wiring? ? ? ? This can be verified; installing a camera to address the malfunction is far more practical than trying to adjust the timing: lol
1. It is not recommended to increase the delay; the emergency stop button is designed for use in emergency situations, and adding a delay will postpone its activation without resolving the issue at its root； 2. If it is necessary to improve both reliability and availability, emergency stop buttons with 3 pairs of contacts can be considered during the design phase, as making changes later will be troublesome ； 3. An unexpected sudden stop must have a cause; circuit problems are the most common ones. Faults in the system’s channels or components will trigger an alarm. It is recommended to conduct routine inspections: check for any issues with the emergency stop button, the wiring box, and the connections on the terminal boards; look for loose or corroded terminals, abnormal cable resistance, and issues related to grounding; also inspect the terminal boards ； 4. Once, the emergency stop button caused the entire device to stop; checks of the wiring and connections from the field up to the mounting brackets showed no issues ； Due to the presence of other emergency stop buttons, this is bypassed within the system; events can be recorded without triggering interlocks ； It was found that faults occurred when someone worked near the cabinet; upon further inspection, it was discovered that the spring opening of the clamping fuse on the FTA terminal board was too large, resulting in a partial connection on one side, and vibrations could cause the connection to break ； The reed opening is due to a fuse burning out during the debugging phase; replacing the fuse required special tools, and attempting to do it by hand caused the reed to deform. Inspections revealed that a small number of other terminal boards also had issues; these were rectified, and standardized procedures were required to be followed.