May I ask about interlocking issues?

It can’t be said that one is better; it depends on your choice.

If your electrical equipment has self-holding functionality, then using pulses is of course the better choice

Of course, pulses are better. First of all, it comes to high-voltage electricity; for safety reasons, it’s best to provide a passive switch for it. Second, the electrical side has a self-locking switch, so there is no need to provide its contacts on a long-term basis.

Let’s talk about the differences between the two options. First: The electrical equipment shuts down once the conditions are met； If the interlock condition is met and the equipment is shut down, it can still be started once the interlock condition is no longer present. Second: When the conditions are met, the electrical equipment cannot be turned on (or it shuts down immediately after being turned on); in other words, the equipment is not allowed to be activated when the interlock conditions are satisfied.

If accident-safe interlocking is to be considered in the design, these two conditions should be energized closed nodes under normal conditions, and the logical relationship should be AND; once either condition is met, the output node loses power and de-energizes. In this case, there is no such thing as pulses or a charged state as you mentioned. Because the interlock causes the shutdown in case of power loss to this output. Currently, the interlock relationships in petrochemical systems are all like this.

My view is slightly different: 1. After an interlock signal is triggered, pulse signals cannot be used for output; using pulse signals may cause restarts and lead to secondary failures. 2. After an interlock occurs, the system must not be restarted until the cause has been identified. Therefore, a self-locking circuit should be added to the interlock circuit, and it can only be reset after the fault is resolved and confirmed manually. Hence, pulse outputs are not suitable, and a self-locking or self-protection mechanism should be incorporated into the output circuit

For devices with high reliability, pulse output is a better choice.

This is a discussion on such issues from another forum; it has been compiled here for further discussion. A pulse is a square wave, which first rises and then falls. It makes it convenient to turn it on again; in fact, applying a pulse signal serves as a reset function. After the action command is issued, it can bounce up again when the water level is high next time. Otherwise, if the command is maintained and stays active without being reset, it will be difficult to establish a connection next time; that’s my understanding. A pulse is what is known as a short signal; a continuous output without pulses is what is known as a long signal. Generally speaking, when the water level is high, pulses cannot be applied to the drain valve, as the actuator cannot maintain its position on its own; a continuous output is necessary at high water levels, and this is also for safety reasons. To control the motor, pulses can generally be applied, provided that the motor’s electrical control circuit has self-holding capability. When using a long signal, in order to ensure automatic reset of the output signal, the motor’s status signal can be used for resetting. We need to check the external circuit, that is, to see if there are any relays or similar components outside as well. It’s actually very simple: if a long pulse is required, I provide a long pulse; if a short pulse is needed, I provide a short pulse. There’s no uniform standard – if the external circuit has a self-holding mechanism, then a short pulse is sufficient. Everything said upstairs is correct. The external circuit has self-locking functionality; the internal logic uses pulses, while those without self-locking use long signals that remain active until the limit alarm signal disappears ； As for how to reset the signal, it needs to be determined based on the actual conditions on site.

My opinion is exactly the opposite: therefore, pulse output should be used, and the output circuit should be equipped with self-locking or self-protection functions. I hope that experts will continue to discuss this issue. This post was last edited by we11we11 on 2009-3-28 at 22:32.]

I agree with all of the above, but I would like to share a personal opinion. Some interlock actions require the use of pulses (of course, electrical systems need to have self-protection mechanisms). For example, in the case of the pyrolyzer fan, it shuts down after an interlock action is triggered, but needs to be turned on again before it can be reset; in such situations, using pulses is a reasonable approach.

Individuals tend to use pulse signals; the output circuit self-locks, and then the reset button releases this self-locking

Still use a pulse signal; the output circuit self-locks, and then the reset button breaks the self-locking!

There has always been this question: if it is used as a growth signal, and if this shutdown signal fluctuates around the shutdown threshold, could it cause the device to start and stop frequently? If it is made into a pulse signal, thanks to self-locking, once the trip signal reaches the set value, the device will continue to operate without being able to stop (which is useful for trip protection), while the device can be stopped using an electrical feedback signal. I also ask fellow sailors to provide the correct answer

Your view is that it isn’t clear what pulses are, and there’s also the important condition of the reset button after a pulse. My approach is to use pulses; more precisely, rising-edge pulses. When a fault occurs and the device’s interlocking conditions are met, protection is activated immediately. The reset button is used to prevent abnormal startup or startup in situations where the fault has not been resolved, thereby enhancing safety and reducing the risk of accidents. As for what someone mentioned earlier about using the normally closed contacts of a relay to control interlocks, it’s a good idea, but it’s a bit off-topic. What if it’s a limit switch instead of a relay? The spring in a limit switch doesn’t have elasticity – so what? Therefore, when responding to a question, it’s necessary to focus on the question posed by the asker and avoid going off-topic.

Pulses are generally used for high-voltage motors, while not needed for others.