User Guide - Eurotherm Ltda

nanodac RECORDER/CONTROLLER: USER GUIDEB2.4.5 AUTOTUNE (Cont.)EXAMPLE 2: AUTOTUNE FROM BELOW SP (HEAT ONLY)The sequence of operation for a heat only loop is the same as that described above for a heat/cool loop,except that the sequence ends at ‘F’ since there is no need to calculate ‘R2G’ (R2G is set to 1.0 for heat onlyprocesses). At ‘F’ autotune is turned off and the process is allowed to control using the new control terms.For a tune from below setpoint ‘CBL’ is calculated on the basis of the size of the overshoot (assuming it wasnot set to Auto in the initial conditions). CBH is then set to the same value as CBL.Note: Autotune can also occur when the initial PV is above SP. The sequence is the same as tuningfrom below setpoint except that the sequence starts with natural cooling applied at ‘B’ after the firstone minute settling time. In this case CBH is calculated and CBL is then set to the same value asCBH.Target SPTrue control point1stovershootPeak topeakPVHysteresisHigh outputLow outputOPB - A = 1 minuteFigure B2.4.5b Autotune heat only process (from below SP)AA to BB to DD to FFStart of AutotuneHeating off for one minute to allow steady state conditions to be established.First heat cycle to establish first overshoot. Cutback low (CBL) value calculated from theovershoot magnitude (unless CBL set to ‘Auto’).Calculate PID terms.Autotune is turned off and the process is allowed to control at the target setpoint usingthe new control terms.Appendix BPage 310HA030554Issue 7 Nov 12