PID Control Configuration in WindLDR for IDEC FC6A PLCs

Quick Answer

The IDEC FC6A includes a built-in PID instruction in WindLDR. The PID block operates in automatic or manual mode with configurable proportional gain (Kp), integral time (Ti), derivative time (Td), and output limits. The FC6A also supports auto-tuning to calculate initial tuning parameters.

PID Fundamentals

PID (Proportional-Integral-Derivative) control continuously adjusts an output to minimize the error between a setpoint and a process variable. The three terms work together: P responds to current error magnitude, I eliminates steady-state offset, and D dampens overshoot.

FC6A PID Configuration

1. Add a PID instruction to the ladder or FBD program
2. Assign the process variable (PV) register — the scaled analog input
3. Assign the setpoint (SP) register
4. Assign the output (CV) register — drives the analog output
5. Configure Kp, Ti, Td in the PID parameter registers
6. Set output limits (min/max clamp)

Auto-Tune Function

The FC6A PID auto-tune function applies a step change to the output and measures the process response to calculate initial Kp, Ti, and Td values. Enable auto-tune by setting the designated special relay for the PID loop. The controller will complete the auto-tune cycle and write the calculated parameters to the PID parameter registers.

Manual vs Automatic Mode

Switch between manual and automatic mode using the PID mode control relay. In manual mode, the operator directly controls the output value. Switching to auto mode enables bumpless transfer — the PID initializes from the current manual output to prevent output jumps.

Example: Temperature Control

A thermocouple input (Type K, 0-500°C) connected to analog input, PID controlling an SSR output for a heating element. SP=200°C, Kp=5.0, Ti=120s, Td=30s. Output limits 0-100% duty cycle.

For cross-platform PID comparison, see the Allen-Bradley PIDE instruction guide.