Allen-Bradley (Rockwell) PLC-5 system

The photograph below shows an Allen-Bradley (Rockwell) PLC-5 system,  used to monitor and control the operation of a large natural gas compressor.  Two racks appear in this first photograph, with different types of I/O cards plugged into each rack:

Like the Siemens 505 PLC seen previously, this Allen-Bradley PLC-5 system is fully  modular and configurable.

Also Read: Difference between Modular and Monolithic PLCs (Top 10 Differences)

The types and locations of the I/O cards inserted into the rack may be altered by appropriately skilled technicians to suit any desired application.  The programming of the PLC’s processor card may also be altered if a change in the control strategy is desired for any reason.

In this particular application,  the PLC is tasked with monitoring certain variables on the gas compressor unit,  and taking corrective action if needed to keep the machine productive and safe. The automatic  control afforded by the PLC ensures safe and efficient start-ups,  shut-downs,  and handling of emergency events.  The networking and data-logging capability of the PLC ensures that critical data on the compressor unit may be viewed by the appropriate personnel. For this particular compressor station, the data gets communicated from Washington state where the compressor is located all the way to Utah state where the main operations center is located.  Human operators in Utah  are  able to  monitor  the  compressor’s  operating  conditions  and issue  commands to  the compressor over digital networks.

Both the Siemens (formerly Texas Instruments) 505 and Allen-Bradley (Rockwell) PLC-5 systems are  considered “legacy”  PLC  systems  by  modern standards,  the  two  systems  in  the  previous photographs  being about 20 years  old each.  It is  not  uncommon to  find “obsolete”  PLCs  still in operation, though.  Given their extremely rugged construction and reliable design, these control systems may continue to operate without significant trouble for decades.

Article from Lessons In Industrial Instrumentation by Tony R. Kuphaldt – under the terms and conditions of the Creative Commons Attribution 4.0 International Public License

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