Chapter 7. PID Built-In Function Block360 PACSystems* RX7i, RX3i and RSTi-EP CPU Programmer's Reference Manual GFK-2950C7.6 Setting Tuning Loop Gains7.6.1 Basic Iterative Tuning ApproachBecause PID parameters are dependent on the process being controlled, there are no predeterminedvalues that will work. However, a simple iterative process can be used to find acceptable values forKp, Ki, and Kd gains.1. Set all the reference array parameters to 0, then set the CV Upper and CV Lower Clamps to thehighest and lowest CV expected. Set the Sample Period to a value within the range Tc/10 toTc/100, where Tc is the estimated process time constant defined in Determining the ProcessCharacteristics.2. Put the PID function block in Manual mode and set the Manual Command (word 14 in thereference array) to different values to check if CV can be moved to Upper and Lower Clamp.Record the PV value at some CV point and load it into SP.3. Set a small gain, such as 100 * Maximum CV/Maximum PV, into Kp and turn off Manual mode.Step SP by 2% to 10% of the Maximum PV range and observe PV response. Increase Kp if PV stepresponse is too slow or reduce Kp if PV overshoots and oscillates without reaching a steadyvalue.4. Once a Kp is found, start increasing Ki to get overshooting that dampens out to a steady value intwo to three cycles. This may require reducing Kp. Also try different SP step sizes and CVoperating points.5. After suitable Kp and Ki gains are found, try adding Kd to get quicker responses to input changes,providing it doesn't cause oscillations. Kd is often not needed and will not work with noisy PV.6. Check gains over different SP operating points and add Dead Band and Minimum Slew Time ifneeded. Some Reverse Acting processes may need setting of Config Word Error Term or OutputPolarity bits.
