VSD control

[Jako13!]

Hi guys does anyone know any standards for estops used along side VSDs. I’ve seen people connect them in a few different ways and wanted to know your opinions. Can we just cut the run signal to the VSD through the systems estop circuit or should we cut power to the VSD all together?

 

[WallaceP]

It really depends on application and risk assessment. I would not be happy just blocking the run signal but I know it is done.

 

[timbobelfast]

Hi guys does anyone know any standards for estops used along side VSDs. I’ve seen people connect them in a few different ways and wanted to know your opinions. Can we just cut the run signal to the VSD through the systems estop circuit or should we cut power to the VSD all together?

Surely the system / plc would need to have feedback to know that an ESD has been operated?

If this is not part of a closed loop then you may create other problems in the process.

Normal practice is for the use of Pilz relays to be drop out control circuits and provide an input to PLC which will result in a complete halt of the process.

Always a bugger to get things reset and up and running again after someone leans on an ESD button!

 

[Jako13!]

Surely the system / plc would need to have feedback to know that an ESD has been operated?

If this is not part of a closed loop then you may create other problems in the process.

Normal practice is for the use of Pilz relays to be drop out control circuits and provide an input to PLC which will result in a complete halt of the process.

Always a bugger to get things reset and up and running again after someone leans on an ESD button!

This is an old system where the emergency stop circuit goes through a relay and the VSD has been retrofitted in. The old motor was DOL so have left everything in place but they have just bypassed the contractor taking power straight to the Drive and the start stop signal comes of that contractor. So when we press the e stop for the system all the contractors for the bit of plant are cut. But obviously all there doing is cutting the run signal to the VSD.

 

[Darkwood]

It sounds like nothing here complies at all with any standards, first you would need to do a risk assessment to establish the safety level/category the safety control system falls into, then you would design the appropriate system to suit the application.
I would recommend you bring somebody in to do this simply because you are asking the question to start with, I'm not suggesting you are not capable of incorporating a compliant system but this stretches beyond a chat on a forum, any advice we offer is based on the info you supply and if any is incorrect or something vital is missed this could lead to incorrect advice and when this is a safety critical system then it is not worth the risk.
I will also add as I do often in similar threads, any upgrade or alteration you make to the control system will put all legal responsibility for the safe functionality of the machine and those using it, as well as this in asking the question it is likely you do not do this kind of work normally and it is highly likely your personal or company insurance will not cover you to do this work so I would be very wary about taking on this task.

A key point in design (safety category in mind) is that the system is fail safe thus simply breaking supplies to contactors or run signals is unlikely to comply.

 

[Jako13!]

It sounds like nothing here complies at all with any standards, first you would need to do a risk assessment to establish the safety level/category the safety control system falls into, then you would design the appropriate system to suit the application.
I would recommend you bring somebody in to do this simply because you are asking the question to start with, I'm not suggesting you are not capable of incorporating a compliant system but this stretches beyond a chat on a forum, any advice we offer is based on the info you supply and if any is incorrect or something vital is missed this could lead to incorrect advice and when this is a safety critical system then it is not worth the risk.
I will also add as I do often in similar threads, any upgrade or alteration you make to the control system will put all legal responsibility for the safe functionality of the machine and those using it, as well as this in asking the question it is likely you do not do this kind of work normally and it is highly likely your personal or company insurance will not cover you to do this work so I would be very wary about taking on this task.

A key point in design (safety category in mind) is that the system is fail safe thus simply breaking supplies to contactors or run signals is unlikely to comply.

Yes I understand your point and I’m very aware of the responsibility placed in the person carrying out the work. It’s more of me trying to get an insight. I’m the type of person who questions a lot of things as I don’t think they are right and I’m sure many people in a maintenance type role understand that there are a lot of people out there with the ‘that will do attitude’ which I am not one hence the reason for trying to get some more info on what the actual requirements are. All our equipment is mainly old equipment where at the time they must have complied by just having an Emergency stop relay. But now I am aware Pilz style units are used so they are fail safe if a contact go welded…… on the system im questioning the emergency circuit goes through a pilz unit then off to all the plants motors etc. Thanks for your help guys and I appreciate your point Darkwood

 

[Darkwood]

Sorry, just looking back you have told me before but we deal with many posts so easily forgot.
I would recommend you look into a few brands of safety control equipment and download their catalogues, many have a full introduction to risk assessment and respective systems that can be applied with examples wiring systems, on basic setups you can often apply the safety system upstream of all the original controls, it gets more involved when you need multi stage systems, braking etc