LINK Systems System 2500 PLS - Manual (Page 48)

System 2500 Operating & Installation Manual - Revision 07 2-40
Figure 9
Probes used with Static,
Normally Closed inputs
An example of the use of a normally closed input is an end of stock sensor, as shown in Figure 9.
A probe is mounted so that it is grounded by the stock being fed into the production machine.
When the end of stock is reached, the probe will no longer contact the stock, opening the input
and causing a fault.