User Guide - Eurotherm Ltda

nanodac RECORDER/CONTROLLER: USER GUIDEB2.4.5 AUTOTUNE (Cont.)FAILURE MODESThe conditions for performing an autotune are monitored by the Tune menu parameter ‘State’. If autotuneis not successful error conditions are read by this parameter as follows:TimeoutSet if any one stage is not completed within an hour. Possible causes are the loop beingopen circuit, or not responding to the controller demands. Some heavily lagged systemsmay produce a timeout if the cooling rate is very slow.TI LimitThis is set if Autotune calculates a value for the integral term which is greater than themaximum allowable (99999 seconds). This indicates that the loop is not responding orthat the tune is taking too long.R2G Limit Error occurs if the calculate value of R2G is outside the range 0.1 to 10.0. R2G limit canoccur if the gain difference between heating and cooling is too large, or if the controlleris configured for heat/cool, but the heating and/or cooling device is turned off or notworking correctly.B2.4.6 Relative Cool Gain in Well Lagged ProcessesIn the majority of processes Relative Cool Gain R2G is calculated by the autotune algorithm as described inthe previous sections.There are occasions, however, where an alternative algorithm may be preferred. These are processes whichare heavily lagged, where the heat loss to ambient is very small so that natural cooling is extremely slow, andcertain high order plants, those that need derivative, Td. This algorithm is known as R2GPD and has beenadded to controllers from firmware version V4.10.The type of algorithm is selected using the parameter 'Tune R2G' found in the Auto-Tune list, sections 4.6.3and 4.7.3. The choices are:-StandardThis is the default as described in example 2 in section B2.4.5. and is suitable for use onmost processes. The benefit of this algorithm is that it is relatively quick. However, inthe type of process described in the previous paragraph, it can produce values whichare not ideal. These values are generally identified by R2G equal to or very close to 0.1.R2GPDIf the process is known to be heavily lagged or produces values such as those abovethen R2GPD should be selected. This algorithm extends the autotune period byputting the controller into proportional plus derivative mode (PD) and uses the outputpower demand value during this period to determine the Relative Cool Gain.OffThe automatic calculation of Relative Cool Gain can be turned off and the value enteredmanually as described in section B2.4.6.HA030554Issue 7 Nov 12Appendix BPage 313