Logic analogous to "timer timing"

[AAbrams]

I'm trying to program an operational safety that requires two buttons to be held in for a set length of time and I don't know how to do this in U90. Is there a feature of the timer that I can use, or do I need to write specific logic to compare the start/run condition with the set time?

THanks in advance for any education you might be able to offer.

Regards,

Alan

[Joe Tauser]

First, the legal aspect - if this is for a press then OSHA requires a dedicated two-hand anti-tiedown relay to run the buttons into.

Now to answer your question - can't you just put two normally open contacts in series to run the timer? If either one is released the timer will reset. If you're trying to verify both were released before the next cycle then it gets a little more complicated - is this what you're trying to do?

Joe T.

[AAbrams]

Yes, this is a safety to keep your hands out of clamp. Right now you've got to press both buttons within a 0.1second window in order to start a clamp. However, once the clamp starts you can release the buttons, which is bad. I want to use a timer to force the operator to keep the buttons engaged. If a button gets released then the clamp should reset and open.

I want to do this without adding new hardware for example a new prox to show the clamp closed.

[AAbrams]

Yes I want an operator to hold 2 buttons while a clamp engages and I want to do it without adding new hardware.

Right now when the buttons are pushed the logic sets a bit which fires a clamp. Unfortunately I can then remove my hands from the buttons. I want to insert a timer which forces those buttons to be engaged or disengages the clamp.

[Joe Tauser]

The right way to do it is to add a sensor to the clamp closed position. A lawsuit will be way more grief than adding a sensor will cause you.

Here's logic that will work if you insist on doing it your way:

Joe T.

[Gabriel Franco]

I´ve done same application but for security reasons using pneumatic switches and AND gate to close clamp and opening it with electrical signal. This way clamp only closes if operator pushes both switches at the same time (With slight time delay).