User manual

PID Loop Operation
(DL450 Only)
Maintenance
and Troubleshooting
8--42
PID Loop Operation (DL450 only)
DL405 User Manual, 4th Edition, Rev. A
S Now, return the Proportional gain to the stable response, for example,
9.7. The error, SP--PV, should be small, but not at zero.
S Next, add a small amount of Integral gain (reset) in order for the error to
reach zero. Begin by using 80 seconds (adjust in minutes if necessary).
The error should get smaller.
S Set the Integral gain to a lower value, such as 50 for a different
response. If there is no response, continue to decrease the reset value
until the response becomes unstable. See the figure below.
S For discussion, let us say that a reset value of 35 made the control
output unstable. Return the reset value to the stable value, such as 38.
Be careful with this adjustment since the oscillation can destroy the
process.
S The control output response should be optimal now, without a Derivative
gain. The example recorded values are: Proportional gain = 9.7 and
Integral gain = 38 seconds. Note that the error has been minimized.