INFICON SID-242 Thin Film Deposition Controller - Manual (Page 74)

Chapter 5 Digital IO
5-1
5.0 Introduction
Digital I/O for the SQS-242 software is handled by an inexpensive Omron CPM2 series
PLC. It is not necessary, however, to use external I/O with the SQS-242 software.
There are several benefits to using an inexpensive external PLC for I/O. First, noisy
high voltage wiring can be placed near the control sources, rather than routed into the
controller’s equipment rack. Only a single serial cable runs from the PLC to the
controller. The PLC also provides electrical isolation for the process controller. And
finally, the PLC’s ladder logic programming provides fail-safe process protection and
allows I/O to be easily tailored to each end user’s installation.
The PLC runs a small ladder logic monitor program that communicates with the SQS-
242 software. The ladder logic program transfers relay and input states from the PLC
connecting block to internal registers. The SQS-242 software reads/writes to those
registers though the PLC’s Comm port. If you need to perform logic functions on an I/O
event, such as AND, OR, or INVERT, it can be easily accommodated by the PLC’s
ladder logic program using Omron’s CX-Programmer software.
Contact Sigma Instruments for more information on programming your PLC.