Switching device from "Manual mode" to "Auto mode" and vice versa.

Hello Everybody!
In our software, we have a feature "Hand mode". The meaning of this is for example if a pump is in "hand mode", we can start the pump manually but on the other hand, if the pump is in "auto mode", PLC can start according to schedule, and so on. If we leave the pump in "hand mode" then PLC can be set to auto mode and continue the work. My question is, should PLC set the pump to "auto mode" and continue the work if possible or the pump should be excluded from the operation (the pump might have issues, so the operator leaves it to "hand mode")? Which one is a reasonable answer and why or it totally depends on the person who is doing the spec?
 
Read your post again--specifically the first two sentences.

Most pump motor controls are done using electromechanical relays and/or contactors, and the "hand mode" is one position of a three position physical switch. The other positions of the physical switch are OFF and AUTO (the switches are sometimes referred to as HOA (HAND-OFF-AUTO) switches). But they aren't software--usually.

Your PLC software might have "hand" and "auto" modes and its possible the relay/contactor doesn't have a physical switch (other than a circuit breaker or electrical disconnect).

But, your post is very unclear and you need to clarify what is software on the PLC and what is (or may be) a physical switch on the pump motor starter.
 
I meant it is an SW state (I am not sure if is it a common convention to HMI/PLC program to have this SW state). It can be applied to any device (for example, a valve, solenoid, pump, motor, etc). Any device can have a state (it can be initializing, starting, opening, manual mode, auto mode, etc depending on the type of device). I just took the pump as an example. I am not sure about this type of mode (handmade and auto mode) is generally accepted SW state or only in our SW. I think this state helps (for example, we have a bug in our SW and we can put the solenoid ON manually to start). My question was, if we have such a state in our SW, should PLC change the mode to auto mode and use the pump if possible? Sorry for not making it clear.
 
Among the many things I learned in my career is that programmers like to do things that (they think) no one else has ever done before. This kind of sounds like that.

However, I've also learned that some manufacturers and control system integrators have very specific reasons for doing things the way they do--quite often it's either a safety requirement or a plant operation specification or standard. This kind of sounds like it could be that, too.

We don't know enough about the process and the plant and the equipment involved, or the materials/chemicals involved. There's just a lot we don't know.

Another thing I've come to know is that people think automation is the answer to just about everything. There are companies (some major manufacturers) that think autonomous plants (including power plants) are going to happen any day. And because one of the biggest costs of any operation is operations and training operators (many of whom leave and take their very expensive training to the plant across the street for 50 cents more per hour) so automation is going to reduce costs AND (allegedly) be safer than human operators.

You need to understand what the reasons might be for this kind of "automatic over-ride" of manual over-ride for the process where you work. It may be "fancy" programming. It may be corporate standard(s). It may be a supplier's requirement for safe operation of their equipment. Without a whole lot of information you haven't provided it is very difficult for someone to say with any degree of certainty or experience if what you are attempting to describe is normal or unusual or some kind of requirement or standard.
 
I assume you are talking about software "handmode" and auto. (aka manual/auto)
There might be very valid reasons for that. We have specific instances where we do this as well, but is the exception rather than normal.
If this should not happen due to specific issues or maintenance requirements the equipment should be "locked out" or isolated to prevent operation. Normal safety protocol.
 
Hello Everybody!
In our software, we have a feature "Hand mode". The meaning of this is for example if a pump is in "hand mode", we can start the pump manually but on the other hand, if the pump is in "auto mode", PLC can start according to schedule, and so on.
This is a very common way to control motors and other equipment on SCADA systems, custom built by integrators or out of the box PCS7, PlantPAx.
It is common to have an Out Of Service/Maintenance mode as well, so if a pump has issues then it is put in OOS mode and can not be changed to Auto, Manual or started until OOS mode has been turned off.
It is up to the person that writes the spec exactly how things work. If you have to put items individually into manual then easiest to return them all to auto when you start the sequence. If groups of items are put into manual then the group should be returned to auto before starting the sequence.
 
It has been my experience that is an operator puts a piece of equipment in Manual Mode, the PLC should not automatically start or stop it, except possible stopping for a safety function (Low Level, etc.). Manual means manual, Auto means auto.
 
I feel I have the same mindset as tdamon. Somebody says PLC should remove the manual mode and start automatically (if it was left to manual mode) when it has a scheduled task to do provided there was no alarm in the device. On the other hand, somebody might leave the device in manual mode (for example the device should not take part in the schedule). Is it just a matter of personal choice or any good reason which one we should follow?
 
I assume you are talking about software "handmode" and auto. (aka manual/auto)
There might be very valid reasons for that. We have specific instances where we do this as well, but is the exception rather than normal.
If this should not happen due to specific issues or maintenance requirements the equipment should be "locked out" or isolated to prevent operation. Normal safety protocol.
May I know when you are switching to auto mode (by PLC) and when not. What are the exceptions you might have?
 
Top