Tim Ganz
Member
Looking at some new equipment we are installing the OEM has 6 estop button stations along the length of the machine.
Each station has 3 N.C. contact blocks of which one set is channel 1 to the safety relay and the second set is channel 2 to the safety relay and the 3 set is to the PLC input card to display on the HMI which button was hit.
In the past I have seen the same setup but having channel 1 and 2 as N.C. and the 3rd contact block back to the PLC as a N.O. contact.
In the PLC you can change your logic to Examine on or Examine off and make it work either way but is there one of these methods better than the other and if so why?
I am just trying to understand the Pro's and Con's of both methods.
Each station has 3 N.C. contact blocks of which one set is channel 1 to the safety relay and the second set is channel 2 to the safety relay and the 3 set is to the PLC input card to display on the HMI which button was hit.
In the past I have seen the same setup but having channel 1 and 2 as N.C. and the 3rd contact block back to the PLC as a N.O. contact.
In the PLC you can change your logic to Examine on or Examine off and make it work either way but is there one of these methods better than the other and if so why?
I am just trying to understand the Pro's and Con's of both methods.