Wavelength Electronics LFI-3751, User Manual

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2
Autotune PID Operation
Chapter 2 - Front Panel Operation
Autotune PID Operation
The LFI-3751 is capable of automatically characterizing your thermoelectric
or resistive heater load and calculating optimum control loop settings
for
P , I , and D .
1. Autotune Process
During an Autotune, the LFI-3751 measures the load’s thermal lag time, L ,
the maximum Temperature versus Time slope, R
max
, and the load’s thermal
time constant, T , for a given output step current, TE I .
The time to complete an Autotune Optimization varies from load to load.
The process occurs in three phases:
Phase 1: The LFI-3751 ramps the thermoelectric current to drive the thermal
load temperature toward the setpoint temperature.
Phase 2: The LFI-3751 performs three characterization passes.
Phase 3: The LFI-3751 reverts to normal operation, saving the optimized
P, I, and D settings in non-volatile memory and settling in at the
setpoint temperature.
When started,
Autotune generates
a step response
to characterize
your system.
TE Current
Time
Your system responds by
going towards the setpoint.
Temperature
Time
R
max
L
T
Ambient
Phase 1
First
Pass
Setpoint
Phase 2 Phase 3
Second
Pass
Third
Pass