Omni 7000 Series - Page 132

OMNI 4000/7000 Operations and Maintenance Guide – Rev F
6-29
Front Panel Operations
8.
a. Use the arrow navigation keys to
scroll down and highlight
Secondary Gain.
b. Press OK.
c. Adjust the Secondary Gain and
integral repeats per minute for stable
control of the secondary variable.
d. Press OK again to save the entry.
9.
Press the Override function key again to
return to the Manual Override screen.
10.
a. Use the arrow navigation keys to
scroll down and highlight
Secondary Setpoint.
b. Press OK.
c. Return the Secondary Setpoint to
the original value so that the primary
variable will be controlled again.
d. Press OK again to save the entry.
Estimate PID Loop Gain
Each process loop will exhibit a gain function. A change in control valve output will produce a
corresponding change in each of the process variables. The ratio of these changes represents
the gain of the loop. For example, if a 10% change in control output causes a 10% change in the
process variable, the loop gain is 1.0. If a 10% change in control output causes a 20% change in
process variable, the loop gain is 2.0.
To provide stable control, the gain of each loop with the controller included must be less than 1.0.
In practice, the controller gain is usually adjusted so that the total loop gain is between 0.6 and
0.9. Unfortunately, the gain of each loop can vary with operating conditions. For example, a
butterfly control valve may have a higher gain when almost closed, than when it is almost fully
open. This means that in many cases, the controller gain must be set low so that stable control is
achieved over the required range of control.
To estimate the gain of each loop for the required range of operating conditions, follow
these instructions:
1.
Go to the Change PID Operating Mode in
Section 6.6.6 and place the PID operating
mode into Manual Mode.
When finished, continue to Step 2.
2.
While in Manual Mode, use the arrow
navigation keys to scroll down and
highlight Manual Value %.
Adjust the control output for the
required flow conditions and note
the process variable values.