NOVA Systems Inc.

January 20, 2016

Early Programable Logic Controllers

Filed under: Legacy PLCs — Tags: , , , — novaadmin @ 8:30 pm

IMG_20160119_142730While returning from Cleveland where I had a Modicon 984 service call, I was contemplating a comparison between the 1990’s equipment and the 2016 equipment. Physical size bordered on gargantuan compared to the micro controllers of today. Approximately 400 I/O would take up the space of a 2 foot wide by 5 foot high bay. The system used coax to connect the I/O processor with the Remote I/O processor.

It is interesting how the software, with segments and networks, is remarkably similar to the modern IEC 61131 code in terms of what are now called Program Organization Units (POU). What is most remarkable is that this stuff is still running with the help of EBay and automation collectors.

Having trouble with an old PLC?  Most likely, Nova can help.  For details contact Kenn Anderson at 414-771-4800 ext 1116 or email


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