N1 PID Loop Object - Metasys - LIT-12011964 - Software Application - System Configuration Tool - 13.2

Metasys SCT: System Configuration Tool Help

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System Configuration Tool
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User Guide
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The N1 PIDL object generates outputs to maintain a measured value at a desired level. The PIDL performs Proportional, Integral, and Derivative control. The PID Loop object manipulates outputs for closed loop control at a given Digital Control Module (DCM101 or DCM140).

Note: For the PIDL object, the only difference between DCM101 and DCM140 operation is that the DCM101 has up to 16 PID Loops, and the DCM140 has up to 20 PID Loops.

The PID Loop object generates outputs for closed loop control by using a collection of inputs and other variables to perform calculations and issue commands. Each PID Loop object can accept up to six analog inputs, and issue commands to a maximum of eight analog outputs. Inputs come from AI objects. Outputs are sent to AOD objects or other PID Loops.

A primary function of the PID Loop object is to perform Proportional plus Integral plus Derivative calculations in order to maintain steady and accurate control of a closed loop. PID calculations take into account the past, present, and future (forecasted) performance of loop inputs for the purpose of adjusting outputs to correct levels. You can configure the PID Loop object to compute any or all of the following:

  • Proportional Only: Present performance is analyzed by computing the difference between the PID Loop setpoint and its feedback. This difference is called an error. With proportional control, the output signal is directly proportional to the difference between the input and the setpoint (that is, the error).

  • Proportional plus Integral: Present and past performance are analyzed in this calculation to affect the output. The error computed in the proportional calculation is now integrated (that is, accumulated over time). If the loop failed to reach setpoint in the past, the integration causes the output to increase or decrease to maintain setpoint.

  • Proportional plus Integral plus Derivative: This calculation uses past, present, and future (forecasted) performance. The derivative part of the computation analyzes the rate of change of the feedback to predict the future value of the feedback. As the feedback changes faster, the PID Loop issues outputs that slow down the rate of change.

You can use the PID Loop object with a variety of control schemes, including sequencing a number of physical devices to maintain control of a closed loop. Additional functions of the PID Loop object include Self-tuning PID Control, bumpless transfer, and an auxiliary switch. Self-tuning PID Control automatically and continually self-tunes the PID Loop to ensure correct feedback levels. The auxiliary switch allows another PID Loop object or a control process to take control of the closed loop. When control of a closed loop is turned over to the PID Loop object, the bumpless transfer function provides for a smooth and predictable transition.