Below is an abstract from a paper entitled, “Power Supply Considerations For Digital Control Systems” by Paul E. Stanley, PE, of Hurst Technologies, Corp. This paper was presented at the 54th ISA POWID Symposium in Charlotte, North Carolina in June 2011.

Power Supply Considerations For Digital Control Systems

Digital Control Systems; Critical AC; Vital AC; Uninterruptible Power Supply Systems; Control System Power Supplies
With the conversion of existing analog instrumentation and control systems to digital systems, the need for careful consideration and planning of power supply systems has become critical to the success of these systems. Instrumentation and control systems, especially microprocessor based systems, cannot tolerate unanticipated power system disturbances. Such disturbances could result in the failure of equipment to perform its intended design function in addition to loss of plant data. This is especially true for nuclear power plants where instrumentation systems are required for safely-shutting down the reactor, mitigating the consequences of an accident, and performing post-accident analysis. This paper will address the most important issues which must be considered in the design, operation and maintenance of power supply systems, as summarized below.
Power Quality – Most digital control systems are provided with power conditioning; however the equipment selected to provide power for these systems should meet an established set of minimum requirements for voltage regulation and noise suppression to ensure that the output of the UPS meets the manufacturer’s requirements for the Digital Control System.
Redundancy – All digital control systems should have more than one power supply, at least one of which will allow for an orderly shutdown in the event of a loss of offsite power.

To find out more about ISA’s Power Industry Symposium in 2012, visit

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