Safe-off board - Whats the purpose?

[pssriram16]

When I use a contactor monitoring circuit, then I pretty much know when the drive (VFD or servo drives) is powered, right? Then why do we have to buy the additional safe-off board (especially to the Powerflex Allen-Bradley drives)? Whats the purpose? Is it to get an additional safety certificate level??

Sriram

 

[controlsdude]

If you use the safe off board you dont have to use a contactor on the input of the vfd. I am assuming your using the external contactor as estop. The safe off board is used also as estop function for different category levels depending on how you wire it in the manual.

 

[pssriram16]

Thanks Controlsdude. The E-stop logic is in the Smartguard controller. When the RESET push button is pressed, then I trigger the external contactor relay and monitor the contact(NC). Then I trigger the "Safe-off enable" signal to drive the safe-off board. Then I trigger the "Drive enable" signal to enable the drive...

I find too much redundancy in this logic, but I guess you are right that this is a requirement for a higher safety category level.

 

[Skogsgurra]

Yes, I can confirm that you need a "hardware safe" and "program error immune" way of doing it. The Safe-Off board is that part of the solution. Usually can't do it in SW only.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[pssriram16]

Thanks Gunnar