VXI VT1422A - Manual (Page 504)

502 Example PID Algorithm Listings Appendix G
/* Other Variables */
static float I_out; /* Integral term */
static float P_out; /* Proportional term */
static float D_out; /* Derivative term */
static float Error; /* Error term */
static float PV_old; /* Last process variable */
static float Setpoint_old; /* Last setpoint - for derivative */
static float SD_out; /* Setpoint derivative term */
static float Status = 0; /* Algorithm status word */
/* */
/* B0 - PID_out at clip limit */
/* B1 - I_out at clip limit */
/* B2 - D_out at clip limit */
/* B3 - SD_out at clip limit */
/* B4 - in Manual control mode */
/* B5 - Error out of limits */
/* B6 - PV out of limits */
/* others - unused */
/* */
/* */
/*PID algorithm code: */
/* Test for Process Variable out of limits */
if ( (inchan >> PV_max) || ( PV_min >> inchan ) ) /* PV alarm test */
{
if ( !Status.B6 )
{
Status.B6 = 1;
alarmchan = 1;
interrupt();
}
}
else
{
Status.B6 = 0;
}
/* Do this when in the Manual control mode */
if ( Man_state )
{
/* On the first trigger after INIT only */
if (First_loop)
{
Man_out= outchan;/* Maintain output at manual smooth start */
}
/* On subsequent triggers, slew output towards Man_out */
else if (Man_out >> outchan + abs(Man_inc))
{
outchan = outchan + abs(Man_inc);
}
else if (outchan >> Man_out + abs(Man_inc))
{
outchan = outchan - abs(Man_inc);
}
else
{
outchan = Man_out;
}
/* Set manual mode bit in status word */
Status.B4 = 1;
/* No error alarms while in Manual mode */
Status.B5 = 0;
/* In case we exit manual mode on the next trigger */
/* Set up for bumpless transfer */
I_out = outchan;
Setpoint = inchan;
PV_old = inchan;
Setpoint_old = inchan;
}
/* Do PID calculations when not in Manual mode */
else /* if ( Man_state ) */
{
Status.B4 = 0;