PID formula for S7-300 and S7-200 - Database & Sql Blog Articles

The FB 41 (continuous controller function block) of the S7-300 and the PID formula of the S7-200 are basically the same, with some minor differences.

In order to avoid the jump of the differential part caused by the change of the given value, the differential part of the S7-200 PID is derived under the assumption that the given value is constant. In order to suppress continuous small oscillations due to the quantization of the controller output, the PID of the S7-300 sets a dead zone nonlinear link. The PID of the S7-300 introduces the disturbance amount DISV, which enables feedforward control. The introduction of differential can improve the dynamic performance of the system, but it is also easy to introduce high-frequency interference. For this reason, the PID of the S7-300 adds a first-order inertial filter to the differential part to smooth the sharp change of the output value. The time constant that can be filtered is 1/5 of the differential time. The FB41 of the S7-300 has more parameters and is more powerful. The FB43 (pulse generator) of the S7-300 is matched with the FB41 to realize PID control of the digital output of the switch.