Expert ForumsInstrumentation and Control

Topic: Re: Installing a close loop for temperature control

posed by 
The correct settings depend upon the dynamics of the process and the objective of the loop but here are some initial guesses for some major types of temperature control applications. I have set the reset time based on typical sizes of the volume (lowest for heat exchanger and highest for column), and set the controller gain based on the time constant to dead time ratio (lowest for heat exchanger and highest for vessel). The rate time is set at 1/10 of the reset time. The first number for a setting is a default if you know nothing about the loop. The numbers in parentheses are typical minimum and maximum values (typical range of settings). If you are outside of the range shown, you have an unusual loop. It is difficult to generalize but I have found these settings to be better than the ones typically set in the configuration by system integrators who are not privy to the process details and dynamics. All loops should be closely monitored when commissioned and tuned with an auto tuner or adaptive tuner.  Application                    Gain                           Reset Time (sec/repeat)                   Rate Time (sec) Heat Exchanger             0.5 (0.2-2.0)                  60 (30-300)                                        6 (3-30) Vessel                          5.0 (2.0-20)                   600 (300-3000)                                  60 (30-300) Column                         2.0 (1.0-10)                   1200 (600-6000)                                120 (60-600)