Created Date: July 09,2010

Created by: joanw

Visit http://learn.automationdirect.com and click on the "PLCs " category. Use the right arrow on the file folders to move over to the "CLICK PLCs " folder tab. You'll find a bunch of tutorial videos on CLICK specifically.

If you want/need even more, check out AutomationDirect's partner in education Doug Bell's online training libraries at www.interconnectingautomation.com -click on "online training ". You can view a library of training videos on a specific topic for as little as $29.95 (unlimited access for one month).

Created Date: August 04,2010

Created by: pj.meza

DOuble Palm Safety Switches

I check the Double Palm Safety Switches example and in the program, the input x003 (E Stop) is use as NC contact. Should it be NO contact? So the signal to the input is ON in order to permit the circuit be activated. If we use a NC contact and I disconnect the wire for the X003, the coil Y001 will be on if X001, X002 and X004 are on.

Phil

Created Date: August 04,2010

Created by: Adisharr

I check the Double Palm Safety Switches example and in the program, the input x003 (E Stop) is use as NC contact. Should it be NO contact? So the signal to the input is ON in order to permit the circuit be activated. If we use a NC contact and I disconnect the wire for the X003, the coil Y001 will be on if X001, X002 and X004 are on.

Phil

It's NC to allow the logic to be true if the E-stop switch isn't active They 're not using the NC contact on the E-stop but the NO contact (for feedback). That might be what's confusing.

I would forget you ever saw this example though as there is nothing 'safe ' about it.

Created Date: August 30,2010

Created by: only1chip

E-stop buttons are often wired with normally closed physical contacts. In fact most of the e-stop buttons for sale by AutomationDirect include ONLY one NC contact. The rationale is: you will want to disable the circuit even if the wires to the e-stop button become damaged or are cut. The logic circuit will "open " either way and the machine will go into it's e-stop routine.

In many cases the e-stop circuit will also be hardwired to a power contactor on the input power to the machine, and if the continuity in the e-stop circuit drops for any reason (operator input OR damage to the circuit) then the machine will lose power. This is done because you typically don't trust a "computer " or "PLC " to perform an orderly shut-down of the machine. The problem might be THAT computer or PLC so you take that possibility out of the equation and simply kill power to the machine.

I think "pj.meza " might not realize that the example expects a NC contact not only in the ladder logic, but also a physical NC contact in the real world. The notes at the top of the example attempt to explain this. If you disconnect that physical NC button - the rung of logic will be permanently disabled.

The use of double palm switches for safety purposes is a widely used industry practice. The theory is that if an operators hands are both required to be on separate momentary switches for the machine to operate - then those hands cannot be "in harms way ". Perhaps their is a better way to explain or design the ladder code for this sort of purpose - if any one has an idea, please forward it to AutomationDirect (or post it here). I'm sure they will give it due consideration.