New to the sight and I am scratching my watch and winding my bottom on this one.

I have a (AC) circuit that is used as part of a safety circuit. I have a metal cage that has to be opened (opening a NO switch) to remove a part then closed (closing the NO switch) to test it under high water pressure. If it fails the cage catches the end plugs. The problem is the operators tie the switch back and run the test without the cage. (letter of warnings, and two terminations has done nothing to stop this) Failure is always a concern but rarely happens. (Maybe 1 in 1000). BUT When it does, and it does happen, it is exposive in nature. 1500-3000 lbs psi of water in a 4,6, or 8 inch pipe sealed on the ends. With the cage open and if/when the threads fail the plugs become missles flying through the air propelled by up to 3000lbs psi of water. The cage covers and captures the PLUGS on the end of the pipe. I want a circuit where the switch HAS to be cycled. If it is tied back the circuit will not run. The switch MUST be cycled (opened then closed again) FORCING the cage to be in place. I know I will have to use a relay or two to accomplish this but not sure how to wire it up. Any ideas? I am at a loss for this one.

Thanks in advance
DaGoose
><>

 

Not enough information. What voltage? What current? Would it be OK to run the logic on DC? etc.

 

What you're looking for is a "anti tie down circuit". There's several ways to do this, mostly it depends on if you want to do it with control logic (as mentioned ) or relay logic.
Give us more info on what's there for controls.

A little more info http://www.burtonpress.com/Controls.htm

 

Voltage at the present time is 120Vac. I did not design the circuit But I get to FIX it. I have thought about an intellegent relay (smart relay). I have tried seveal things with the switches and they manage to by-pass it everytime. I have used 1CR with the switch more or less in the E-STOP circuit. The entire circuit is relay logic at the present time.

 

An easier route might be a magnetic or prox type of switch that's harder to bypass.

 

I would put some type of self contained transponder (e.g. RFID) on the cage , and a receiver immersed in the tank.The subsequent control circuit is easy enough and the system is foolproof. No cage , no go, simple as that.

Whether this is feasible or not in your particular case, depends on tank size and the relationship between tank size & cage size.There should be no difficulty getting water resistant components suitable for your application.

 

How about a circuit that would sense the switch closing and give a time limit, like anything from 1 second to 5 minutes, and then it wouldn't reset until the switch was opened and closed again?

 

Here's a switch that takes a unique key type actuator that actually fits inside the switch.
http://www.omron247.com/doc/pdfcatal.nsf/CB63870AFED2AD2286256CEE006C235B/$FILE/D31D4DS0303.pdf
it's from Mouser Electronics

 

How about a keyed enclosure or something around the switch?
or move the switch somewhere else?

I'd look for a simple mechanical solution first.

 

Here's a switch that takes a unique key type actuator that actually fits inside the switch.
http://www.omron247.com/doc/pdfcatal.nsf/CB63870AFED2AD2286256CEE006C235B/$FILE/D31D4DS0303.pdf
it's from Mouser Electronics

That's a simple/good idea too. We have a few of those at my work and no one messes with them.

 

I now have an avenue (several really) to go down that I hadn't thought of before. Thanks again for your help. I will be back to this sight just to read up on STUFF and learn something new. Who says ya can't teach an old dog new tricks! Thanks again

Greg

 

Here's a switch that takes a unique key type actuator that actually fits inside the switch.
http://www.omron247.com/doc/pdfcatal.nsf/CB63870AFED2AD2286256CEE006C235B/$FILE/D31D4DS0303.pdf
it's from Mouser Electronics

This is the Avenue we took. Thanks so much for your help.