Let’s discuss a simple issue related to motor control DO points
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A simple motor start/stop can be achieved using 1 DO or 2 DOs; it’s just that the secondary circuit differs. But how is it decided which method to choose? What are their respective advantages and disadvantages? Are there any special mandatory requirements for various occasions?
I believe that it should be determined based on the fail-safe configuration of the system, such as fail-safe type or fail-closed type.
It depends on how the control principles in the electrical engineering field are designed. For example, if the remote control circuit in the electrical engineering field does not have a self-locking mechanism, then the instrumentation team only needs to output one DO signal, which must be maintained continuously. If the electrical engineering field does have a remote self-locking mechanism, then the instrumentation team needs to set up two DO signals: one for starting and one for stopping. In electrical engineering, remote self-locking is generally not implemented in the control circuits of low-voltage equipment, whereas it is usually included in the control circuits of high-voltage equipment
Indeed, this is not determined unilaterally through control. But when considering a project as a whole, what is the basis for determining how it should be designed?
Actually, I have some doubts about this as well. For example, a single DO might pose a safety risk due to the device starting up automatically after a power outage, but a dual DO could also fail to shut down in the event of a circuit fault – in both cases there are safety issues.
The single DO can utilize reset and RS flip-flops to address security issues, while the dual DO does indeed pose such a security risk. This brings us back to the type of fault mentioned earlier. The fail-safe design should be such that it stops without excitation ； The non-fault-safe type should be designed for excitation shutdown. Since dual DOs are chosen, this implies fail-safe operation; currently, SIS requirements mandate fail-safety.
I agree with the view above; whether it’s a single DO or a dual DO, safety should be the top consideration, along with availability. This question is similar to that of valve cut-off valves: whether to choose a single-coil solenoid valve or a double-coil solenoid valve.
The prerequisite for a single DO to be able to reset is that the control system has sufficient backup power supply time, right? There should also be corresponding power-off protection interlocks. If the disadvantages of a single DO can be addressed, then what are the advantages of a dual DO?
Advantages of dual DOs: It is possible to avoid unplanned stops caused by unnecessary external factors, provided that this type of interlock is a non-safety interlock system; design specifications allow non-safety interlock systems to be designed as live-interlocked systems. Additionally, in connection with what was mentioned on the third floor regarding the issues with high-voltage and low-voltage electrical motors, I consulted with the electrical team. As stated on the third floor, there are two closing and opening coils for high-voltage motors, while there is only one such coil for low-voltage motors. The choice between high-voltage and low-voltage motors is determined by the equipment itself. Moreover, it doesn’t matter to the electrical system whether one DO or two DOs are provided for the instrument; by providing it with one DO, the electrical system can use relays for expansion.
The latter part is the question of whether the chicken or the egg came first; the electrical team says it can be adjusted through control, while the control team says it should be done according to the electrical design. And why did I think of this question? It’s because in some situations, one has to decide between the two, and it’s hard to know what to do:P