VXI VT1422A User Manual
Page 494
492 Example PID Algorithm Listings
PIDA Source Listing
/********************************************************************************************/
/* I/O Channels
*/
/* Must be defined by the user
*/
/*
*/
/* inchan - Input channel name
*/
/* outchan - Output channel name
*/
/*
*/
/********************************************************************************************/
/*
*/
/********************************************************************************************/
/* PID algorithm for VT1422A controller module. This algorithm is called */
/* once per scan trigger by main(). It performs Proportional, Integral
*/
/* and Derivative control.
*/
/*
*/
/*
*/
/* The output is derived from the following equations:
*/
/*
*/
/* PID_out = P_out + I_out + D_out
*/
/* P_out = Error * P_factor
*/
/* I_out = I_out + (Error * I_factor)
*/
/* D_out = ((Error - Error_old) * D_factor)
*/
/* Error = Setpoint - PV
*/
/*
*/
/* where:
*/
/* Setpoint is the desired value of the process variable (user supplied) */
/* PV is process variable measured on the input channel
*/
/* PID_out is the algorithm result sent to the output channel
*/
/* P_factor, I_factor and D_factor are the PID constants(user supplied) */
/*
*/
/*
*/
/* At startup the output will abruptly change to P_factor*Error
*/
/*
*/
/*
*/
/********************************************************************************************/
/*
*/
/* User determined control parameters
*/
static float Setpoint = 0; /* The setpoint
*/
static float P_factor = 1; /* Proportional control constant
*/
static float I_factor = 0;
/* Integral control constant
*/
static float D_factor = 0; /* Derivative control constant
*/
/*
*/
/* Other Variables
*/
static float I_out;
/* Integral term
*/
static float Error;
/* Error term
*/
static float Error_old;
/* Last Error - for derivative
*/
/*
*/
/*PID algorithm code:
*/
/* Begin PID calculations */
/* First, find the Process Variable "error" */
/* This calculation has gain of minus one (-1) */
Error = Setpoint - inchan;
/* On the first trigger after INIT, initialize the I and D terms */
if (First_loop)
{
/* Zero the I term and start integrating */
I_out = Error * I_factor;
/* Zero the derivative term */
Error_old = Error;
}
/* On subsequent triggers, continue integrating */
else /* not First trigger */
{
I_out = Error * I_factor + I_out;
}
/* Sum PID terms */
outchan = Error * P_factor + I_out + D_factor * (Error
- Error_old);
/* Save values for next pass */
Error_old = Error;