Emerson Micro Motion 3711, Configuration And Use Manual, Page: 112 / 234

104 Micro Motion
®
Model 3711 Gas Flow Computers
PID Control Loops
Note: Even if Mode is set to Manual, the PID control function is monitoring input values and
performing other functions that require processor resources. To configure the unit so that no
processor resources are consumed by the PID control function, disable the Scanning parameter.
8. Enter a value for
Loop Period
. This parameter defines the minimum time period that must
elapse between the beginning of one execution of the PID algorithm and the beginning of the
next execution. If an override loop is implemented, the PID algorithm will be executed for
both loops within the specified time period.
9. Define the
Primary
loop, and the
Override
loop if required.
a. Using the
Select TLP
dialog box, assign a process variable to the loop by specifying the
point from which it will be read (e.g., an analog input or pulse input).
b. Enter the Setpoint value to be used as a target for the loop process variable. Enter the
value in the EU used by the point assigned in the previous step.
10. If Output Type is set to Analog , define the Output Point :
a. Using the
Select TLP
dialog box, specify the analog output that will be used to implement
PID control. The primary loop and the override loop use the same analog output.
b. If desired, enter an initial value for the analog output. This value is applied only in manual
mode, and is used to avoid bumps in the analog output level at system startup.
c. Ensure that the analog output is configured correctly. See Section 7.5.
If Output Type is set to Discrete , define the DO Open Point and the DO Close Point :
a. Using the
Select TLP
dialog box, specify the discrete output that will be used for
open/forward control.
b. Using the
Select TLP
dialog box, specify the discrete output that will be used for
close/reverse control.
c. Ensure that the discrete outputs are configured correctly. See Section 7.7.
11. If an override loop is implemented, click the Tuning button in the PID Loop window. The
window is expanded to include additional parameters and controls as shown in Figure 10-2.
Set
Override Type Select as required:
• If set to
High
, the output is controlled by the PID control loop that requests the greater
adjustment.
• If set to
Low
, the output is controlled by the PID control loop that requests the lesser
adjustment.