PID-functions

Set of helper functions to initiate and update a PID control loop

Description#

PID_new( pid[], Float:set, Float:out ) // set up new PID

PID_dir( pid[], direction ) // set direction of control

PID_set( pid[], Float:set ) // adjust the target value

PID_tune( pid[], Float:Kp, Float:Ki, Float:Kd ) // set the P, I, D parameters

PID_limits( pid[], Float:min, Float:max ) // set the control range

PID_update( pid[], Float:in ) // update PID with feedback, and return new control value

Parameters#

`set`	setpoint / target
`out`	Initial output value
`direction`	1 (normal) or -1 (reverse)
`Kp`	Proportional component
`Ki`	Integral response component
`Kd`	Derivative response component
`min`	Smallest output value allowed
`max`	Largest output value allowed

Return value#

The PID_update function returns the calculated output value.

Example usage#

 
   new p[PID];  // create a PID 
 
   main() 
   {
      // Initialize the PID with target and no output
      PID_new(p, 50.0, 0.0);
 
      // Limit output to +/- 10
      PID_limits(p, -10.0, 10.0); 
 
      // Set the tuning parameters 
      PID_tune(p, 0.2, 0.04, 0.01);
 
      // Set update speed to 100ms
      SetTickInterval( 100 );
   }
 
   @Tick(uptime) 
   {
      new Float:psi;      
      new Float:v;
 
      // Read and scale a sensor input (0-100psi from 4-20mA sensor)
      psi = 100.0 * ((GetInputValue(1, INVAL_RAW)-4000)/16000);
 
      // Update the PID with the feedback value
      v = PID_update(p, psi);
 
      // Apply to output
      SetOutput(4, fround(v+50));
   }

NOTE: The values used in the above example are not from a real world setup. Please make sure you understand how PID works and how to correctly tune the variables if you use any of the PID functions.

Last updated Mar 30, 2022