KPF: Pre-Observing | Observing | Post-Observing
Lakeshore Control Recovery
- Josh Walawender
Analytics
In case the Lakeshore thermal control is disconnected at any point, recovery cleanly should be possible with the procedure below.
Each Lakeshore control loop is configured by a family of keywords. The individual keywords have three letter suffixes on each base to differentiate the differetn keywords. The entire family of keyword is quite extensive. For example, the green detector is controlled by the STA_CCD% family under the kpfgreen service:
[kpfeng@kpfserver] ~ > gshow -s kpfgreen STA_CCD%
STA_CCD_T = -100.000 degC
STA_CCDARN = On
STA_CCDCHI = A
STA_CCDCHO = 1 channel
STA_CCDCMP = On
STA_CCDDER = 15.0
STA_CCDDIS = Current
STA_CCDDOT = 0.00 deg C/min
STA_CCDINP = A
STA_CCDINT = 20.0
STA_CCDLIM = 0 degrees K
STA_CCDMAX = 1.000 amps
STA_CCDMOD = Closed loop PID
STA_CCDOHM = 50
STA_CCDOUT = 13.8 percent
STA_CCDPOW = Off
STA_CCDPRO = 250.0
STA_CCDRMO = On
STA_CCDRMP = 0.2 deg C/min
STA_CCDRNG = Medium
STA_CCDRNI = 1000 ohm
STA_CCDSTA = No errors
STA_CCDTRG = -100.000 deg C
STA_CCDTRI = <undef>
STA_CCDTRK = Off
STA_CCDTRO = 0.000 deg C
STA_CCDTRS = -100.000 deg C
STA_CCDTYP = Platinum RTD
STA_CCDUNI = Celsius
STA_CCDVAL = -100.000 deg CHere is a list of the families as currently defined:
Function | Keyword Service | Family Base Name |
|---|---|---|
Green Detector |
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Green Cold Finger Base |
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Green Cold Finger Tip |
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Green Cold Head |
|
|
Red Detector |
|
|
Green Cold Finger Base |
|
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Green Cold Finger Tip |
|
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Red Cold Head |
|
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Green Cryobody |
|
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Red Cryobody |
|
|
Procedure
First, turn off the control loop by setting the heater power to off. This is done by setting the appropriate RNG keyword to “off”. For example, if I were doing this for the green detector: modify -s kpfgreen STA_CCDRNG=Off. This ensures that on restoration, the system will not immediately power up to some large heater power.
Second, we must restore thermal control, but we want the target temperature to match the current temperature. This again prevents sudden changes in output. To do this we set the RMO keyword to “Off” which turns off ramping (the set point will change immediately), then we set the TRG keyword to the value reported by the VAL keyword, then we set the RMO keyword back to “On”. This can all be done in a single command. In this example, we are changing the green detector control loop:
modify -s kpfgreen STA_CCDRMO=Off STA_CCDTRG=`gshow -s kpfgreen STA_CCDVAL -terse` STA_CCDRMO=On
Third, now that the set point and current value are similar (check that TRG and VAL are close), we can restore the heater output by setting RNG back to the original value (use keyword history to determine if the range should be high, medium, or low). For example, on the green detector: modify -s kpfgreen STA_CCDRNG=Medium.
Finally, we can restore the target set point by modifying TRG. For example, on the green detector: modify -s kpfgreen STA_CCDTRG=-100
Note that the Lakeshore ramping is a control on the instantaneous target set point. The TRG keyword will reflect that, so when you set TRG to some value, it will not immediately go there, but will report intermediate values as it ramps using the rate in the RMP keyword. The TRS keyword will show you the last user defines TRG value which should be the final target set point of the system.