THORLABS MTD415T, Техническое описание

Страница: 21 / 30

© 2016 Thorlabs GmbH
7 PID Tutorial
21 MTD415T Data Sheet Rev. 1.0
Example:
"
P3000 "; " T25100 " -> the loop still oscillates
" P2000 "; " T25000 " -> the loop stopped oscillating
·
If the loop stopped oscillating, increase the P share, change the set set temperature for
0.1K and observe the loop behavior.
Example:
"
P2500 "; " T25100 " -> the loop oscillates again
·
Repeat above steps.
Example:
"
P2200
"; "
T25100
" -> the loop stopped oscillating.
"
P2300
"; "
T25000
" -> the loop oscillates again
" P2250 "; " T25100 " -> the loop still oscillates
" P2200 "; " T25000 " -> the loop stopped oscillating
·
By this approximation of the P share, a value can be found at which the loop starts to
oscillate.
In our example, this happened at P = 2250 mA/K.
Read oscillation period at this value - for example, 5.58 sec.
The critical gain and the critical oscillation period are found.
4. Program the MTD415T with these values in order to trigger the calculation of the PID shares
and the cycle time by the firmware:
Program the critical gain to the found above value: "
G2250 "
Program the critical oscillation period: " O5580 "
5. The firmware calculates the parameters of the digital PID loop and applies them instantly.
The calculated parameters can be read out using the following commands:
"
P? " " [1350<LF>] " -> P share = 1350 mA/K
"
I?
" "
[161<LF>]
" -> I share = 161 mA/(K*s)
"
D?
" "
[941<LF>]
" -> D share = 941 (mA*s)/K
" C? " " [87<LF>] " -> Cycle time = 87 ms
6. Usually, at this point the PID optimization for the settling behavior is finished. If required, the
PID values and the cycle time can be manually fine tuned in order to optimize the loop
response to changes of the thermal load.
7. As a final step, save the settings to the non-volatile memory: " M "
Notes
·
The cycling time is the time base of the internal digital control loop and is calculated
automatically by entering G (critical gain) and O (critical oscillation period).
·
If manually changing the cycling time ("C"), the firmware calculates the I and the D share
anew.
·
The optimized PID parameters are valid for a steady state, that depends on the set
temperature as well as on the ambient conditions (ambient temperature, temperature of the
thermally controlled object). Any changes of the operating and/or environmental conditions
may require a re-adjustment of the PID parameters.