Wavelength Electronics LFI-3751, User Manual

Page: 58 / 132

58
Chapter 2 - Front Panel Operation
Manually Setting the P, I, and D Constants
Manually Setting the P, I, and D Constants
Selecting optimum PID control parameters tha minimize overshoot and
maximize stability is even easier now when using the LFI-3751 with Autotune
PID. Refer to Autotune PID operation on page 23 for a detailed description of
the Autotune feature. The LFI-3751 can be confi gured to operate as a
P, PI,
PD , or PID temperature controller.
The following sections discuss how to manually adjust the P , I , and D
constants.
•
For most small loads, set the Proportional Gain to 30, the Integral Time
Constant to 1 second, and Differentiator Time Constant to OFF (0).
•
The P, I, and D settings are saved in non-volatile memory.
•
When fi rst controlling a load, adjust only the P term while leaving the I
term at 1 second and the D term OFF. If the load will not stabilize for any
P term, then increase the I term to 2 seconds. Again, adjust the P term
to optimize the system. Repeat these steps until the load temperature
stabilizes around the setpoint temperature. Use the
D term to reduce
overshoot and to damp the system.
P ACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
decrease
increase
1. Adjusting the P Term
•
Rotate the Display Select Switch to P (Shift Button ON) .
•
Rotate the Digi-Pot Adjust Knob to change the displayed value.
•
The Proportional Gain range is AutS, Autd, and 0 to 100.
•
RS-232 Command: [P]
•
Increasing the proportional gain will improve overall temperature stability.
Since most thermal systems are “gain limited”, too high a proportional
gain can cause thermal cycling or instability in the instrument’s control
loop. If you notice the temperature of your load cycling around the setpoint
temperature, then reduce the proportional gain.
Display Proportional Gain
Default P, I, & D Constants
= 30
= 1 second
= 0 (OFF) P
I
D
[P]
[I]
[D]
P ACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
Auto Setpoint
Auto Disturbance
OFF
ON
Proportional Gain Range
AutS
Autd
0.0
0.1 to 100