I am a new programmer, and I have a welding fixture with multiple stations.
I am adding prox switches to decide when to skip a particular station but I would like to add a ‘sanity check’
to see that the state of the prox switch changes to make sure the part has been replaced and to also
confirm the prox switch isn’t broken.
If the prox switch doesn’t change state and/or the prox switch indicates an empty station, do not weld at this fixture.
Can anyone offer any insights?
There are many ways to achieve this. Beneath is a fairly simple one made on an e-series. It uses If-commands to check the sensor before and after using it. 
You could monitor the state of all the prox switches in a thread and set a variable.
At the end of the prog add a loop (that checks the state of the variable to be false before ending the program) with a pop up / error if all parts have not been unloaded or a proxy stays true.
Hope this helps
Thanks much…
