User manual

PID Loop Operation
(DL450 Only)
Maintenance
8--41
PID Loop Operation (DL450 only)
DL405 User Manual, 4th Edition, Rev. A
It is not necessary to try to obtain the best values for the P, I and D parameters in the
PID loop by trial and error. Following is a typical procedure for tuning a temperature
control loop which you may use to tune your loop.
Monitor the values of SP, PV and CV with a loop trending instrument or use the PID
View feature in DirectSOFT (see page 8--49).
NOTE: We recommend using the PID View to select manual for the vertical scale
feature, for both SP/PV area and Bias/Control Output areas. The auto scaling
feature would otherwise change the vertical scale on the process parameters and
add confusion to the loop tuning process.
S Adjust the gains so the Proportional Gain = 0.5 or 1.0 (1.0 is a good
value based on experience), Integral Gain = 9999 (this basically
eliminates reset) and Derivative Gain = 0000. This disables the
integrator and derivative terms, and provides some proportional gain.
S Check the bias value in the PID View and set it to zero.
S Set the SP to a value equal to 50% of the full range.
S Now, select Auto Mode. If the loop will not stay in Auto Mode, check the
troubleshooting tips at the end of this chapter. Allow the PV to stabilize
around the 50% point of the range.
S Change the SP to the 60% point of the range.
The response may take awhile, but you will see that there isn’t any oscillation. This
response is not desirable since it takes a long time to correct the error; also, there is a
difference between the SP and the PV.
S Increase the Proportional gain, for example to 2.0. The control output
will be greater and the response time will be quicker. The trend should
resemble the figure below.
S Increase the Proportional gain in small increments, such as 4, 6, 7, etc.
until the control output response begins to oscillate. This is the
Proportional gain that should be recorded.
Manual Tuning
Procedure