Skip to content
November 3, 2011 / Kasey Mirecki

PLCs PID Control – Speed Control Loop (Part 2 of 2)

A good example of a speed control loop is the action taken when adjusting the speed of the belt (or conveyor) to maintain the speed at a desired RPM (or Travel Time). This typically involves an encoder mounted on the belt/conveyor, connected to a PLC high-speed counter (HSC) used as a feedback to measure its speed. Based on this feedback PID perform a control action to adjust the analog output (or pulse with modulated output signal – PWM) until the process speed stabilizes at the desired set point (SP) value.

The sensed encoder feedback is the process variable or process value (PV). The desired speed is called the set point (SP). The output of the process (analog output, PWM) is called the manipulated variable (MV). The difference between the speed detected (HSC) and the set point is the error (e) and quantifies whether the speed is too high or too low and by how much.

Hardware requirements for this application:

  • PLC with transistor outputs for PWM speed control, or
  • PLC with analog output expansion module
  • Touch-screen (GT series, GN series or GV series) as machine interface to make system adjustments.

All Panasonic PLC’s supports High Speed Counter input but frequency varies base on PLC type and series. Measurement of HSC needs to be calculated before using in speed control PID Function Block. (raw data of HSC would be increasing value and need to be processed in PLC interrupt and calculate to RPM or frequency for example)

Demo programming software can be downloaded from Panasonic Electric Work website.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: