Supervisory Control Systems

SCS Interface

Like I like to do, I’ve been doing some reading about compressed air and compressed air control.  A few weeks ago I wrote about throughput control and I’ve been going over a case study about supervisory control systems (SCS).  These are the devices which dictate primary and secondary compressor system operation to maximize not only throughput, but efficiency too.

In the same blog mentioned above I discussed the methods used to control a compressor, and the other side of that equation is the actual controller which is giving the commands.  These supervisory type of controls are happily routed through a PLC so that, for example, when the discharge flow spikes, a suction throttle valve can be cycled on to restrict the intake flow.  A feedback loop that functions in real time, with controlled set points, can take a compressed air system to the next level.

In the photo at the top of this blog a sketch of the SCS for a hybrid system is shown.  This is from a case study which walks through the blending of a centrifugal compressor and a reciprocating compressor.  On the surface this sounds like it may be complicated and in actuality it’s extremely complicated.  Apparently the biggest problem is heat accumulating as a result of load fluctuations.  In addition to the heat load, there’s the logic needed to allow each compressor to start in sequence, independently, or manually.  For this application, the solution was found using two main lines and two sub lines of ladder logic.  Simple and clever at the same time!

SCS Ladder Logic

Do you have a similar setup to share or interest in this particular case study?  Email me at and we can correspond directly.

Lee Evans
Application Engineer

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