ILX Lightwave LDT-5900 Series User Manual page 40

2
C H A P T E R
After the temperature has stabilized, the integral term (I term) is then added to the
control loop (Point 5 on Graph). The I term is then increased until it causes the
temperature to oscillate around the user defined tuning set point (Point 7 on
Graph). The final I term coefficient is set to 33% of the I term value that is found to
start oscillations in the temperature control loop.
This tuning method calculates PID coefficients that result in fast settling times and
good set point stability. The auto tune algorithm slowly moves towards the
oscillation points of the thermal system to consistently find suitable PID
coefficients on a wide range of thermal systems, and to ensure that the thermal
system will not be damaged. The calculated PID coefficients are dependent upon
the user defined current limit and setpoint temperature. If a new setpoint
temperature is desired that would require the controller to cool (vs. heat), the
Auto-Tune feature can be used to calculate optimal PIDs for the new temperature
setpoint. The tuning times of the auto tune process will range from 10 to 45
minutes, or more, depending on the thermal system being tuned. Typical tuning
times are around 25 minutes. Thermal systems with higher P, I and D coefficients
will take more time to tune than those with lower P, I and D coefficients.
To utilize this feature:
• Connect the temperature controller to the desired thermal load.
• Verify the current limits and temperature set point are set appropriately for the particular TEC.
• Press the Parameter SELECT button to activate the PID / AUTO-TUNE parameter.
• Auto-Tune should be highlighted with brackets.
• If the status from a previous Auto-Tune is shown next to the [Auto-Tune] selection (i.e.
"Success" or "Failed"), press the ENTER / LOCK key to clear it.
• Press the ENTER / LOCK key to begin..
While Auto-Tune is in process, the PID/AUTO-TUNE LED will be flashing and the
thermal system's temperature will be displayed. Once an Auto-Tune is complete,
the instrument will then beep and disable the output, and the display will read
"AutoTune Success". The instrument will automatically enter the new P, I and D
values from a successful Auto-Tune.
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LDT-5980/ 5948
O P E R A T I O N S
Front Pa nel Opera t ion
LDT-59XX
[Auto Tune]
P: 00020.00
TEMPERATURE CONTROLLER