Hello gentlemen,
I had a discussion with the manufacturer of a pneumatic overhead door open that intrigued me and wondering if the information they provided was accurate.
Most if not all overhead door openers, electrical or otherwise, have option to wire safety devices to the controller to reverse the door if it's coming down and to stop it from coming down if the door is fully open. One such safety device is a safety edge sensor, usually pneumatic, and since it will eventually make contact with the floor there's always a switch of some sort turn it off before hitting the floor.
The way they built their controller is as follows:
The safety devices input on the controller is wired directly (circuit board trace) to the output that opens the door( technically I believe it's wired to a relay on the board that turns off the close solenoid valve and turns on the open) and the reason is UL certification. According to them UL (and probably CSA) required the safety device to go directly to the open device (or relay) as they did not want error in software (program logic) to cause the safety to not work as expected.
So to prevent the door from going up when it hits the floor they also connected that relay to an open command input on the controller. So two things happen at the same time, activate the open solenoid and activate the open input on the controller so that the software would recognize that the door is going to open and checks the door's position via an absolute encoder and if the door is closed it turns off that relay again.
Anyone knows of a similar UL requirement in any other application?
If the software is able to influence the relay that opens and is capable of preventing it from continuing doesn't that defeat their requirement anyway?
I'm likely to just wire the pneumatic switch trough a read switch and have it turn off that way as it sometimes still goes up after hitting the floor ( I'll spare you the details as to why/how). But I would like to know if there are other ways, devices, programming techniques, safety relays or anything that would be suitable for this application.
Thanks
Kal
I had a discussion with the manufacturer of a pneumatic overhead door open that intrigued me and wondering if the information they provided was accurate.
Most if not all overhead door openers, electrical or otherwise, have option to wire safety devices to the controller to reverse the door if it's coming down and to stop it from coming down if the door is fully open. One such safety device is a safety edge sensor, usually pneumatic, and since it will eventually make contact with the floor there's always a switch of some sort turn it off before hitting the floor.
The way they built their controller is as follows:
The safety devices input on the controller is wired directly (circuit board trace) to the output that opens the door( technically I believe it's wired to a relay on the board that turns off the close solenoid valve and turns on the open) and the reason is UL certification. According to them UL (and probably CSA) required the safety device to go directly to the open device (or relay) as they did not want error in software (program logic) to cause the safety to not work as expected.
So to prevent the door from going up when it hits the floor they also connected that relay to an open command input on the controller. So two things happen at the same time, activate the open solenoid and activate the open input on the controller so that the software would recognize that the door is going to open and checks the door's position via an absolute encoder and if the door is closed it turns off that relay again.
Anyone knows of a similar UL requirement in any other application?
If the software is able to influence the relay that opens and is capable of preventing it from continuing doesn't that defeat their requirement anyway?
I'm likely to just wire the pneumatic switch trough a read switch and have it turn off that way as it sometimes still goes up after hitting the floor ( I'll spare you the details as to why/how). But I would like to know if there are other ways, devices, programming techniques, safety relays or anything that would be suitable for this application.
Thanks
Kal
