FourStar Software Documentation

The Observatories of the Carnegie Institution for Science (Carnegie Observatories), Pasadena, CA

2009-04-20

Christoph C. Birk (birk AT obs DOT carnegiescience DOT edu)

Location of this document: http://instrumentation.obs.carnegiescience.edu/Software/FourStar/sensors.html

FourStar Sensors

The FourStar software monitors 18 cryogenic temperature sensors, two of which are actively controlled, utilizing two LakeShore-340 temperature controllers. The detector temperature is held at 80 K while the optics module is kept at 200 K. During cooldown the software acts as a meta-controller by adjusting the setpoint of the LakeShore controller every minute to create a cooldown ramp with a slope of 0.3 K/min to protect the H2RG arrays from sudden temperature drops. During warmup the temperature setpoints for the detector and optics are increased in sync to ensure that the optics and detector reach room temperature at the same time.
The system logs all temperature and heater data and creates graphs for all sensors, typically displaying the last 18 hours of data, even though other time periods may be selected.
Cryo Temperatures
Temperature Controllers
Temperature Monitors

LN2 Process Controller
Auto-Fill System

Graphs
Temperature Controller Graphs
Temperature Monitor Graphs
LN2 Graphs
FourStar Software Documentation

Cryo Temperatures

The Temperature main menu contains the following menu entries:
Show TempGraph
Opens a temperature graph for the currently active (foreground) temperature-controller or -monitor.
Show PowerGraph
Opens a power graph for the currently active (foreground) temperature controller.
Edit GraphPars
Opens a dialog box that allows to edit the graph parameters.
Create PDF
Creates a PDF-file of the active (foreground) graph.
Edit TunePars
Opens a dialog box that allows to edit the tuning parameters of the foreground temperature controller.
Equalize Channels
Calculates the average of all active channels of the foreground temperature monitor and stores the offsets of each channel in the preferences file. These offsets are then subtracted from the actual temperature readings to remove small differences between the temperature sensors.
Note: This should only be done when the dewar is in a temperature equilibrium, ie. all temperature sensors are at the same temperature.
Re-Open Connection
Recover the communication to the (foreground) temperature controller or monitor.
Lock/Unlock GUI
Lock (or unlock) the editable fields of the (foreground) temperature controller. The edit-windows are locked by default. This avoids the accidental change of any setting by the user.

Temperature Controllers

The FourStar dewar maintains two separate temperature regimes. The detector is actively controlled to maintain a constant temperature of 80 [K]. The Optics barrel must be controlled at 200 [K]. A third temperature controller is used during warmup only. It heats up the dewar tanks to speed up the warmup.
Each temperature controller has it's own window with identical control elements:

Current Temperature
Displays the current temperature in deg. Kelvin.
Target Temperature
Sets the target temperature for the Meta controller. When the Meta controller is active (see below) the controller GUI updates the setpoint of the temperature controller at the Max Gradient rate until the setpoint of the Lakeshore temperature controller reaches the target.
Current Gradient
Displays the the current temperatures change (deg. Kelvin per minute).
Max Gradient
Maxium allowed temperature change per minute. This should be 0.5 deg/min for the detector and about 0.1 deg/min for the optics barrel.
Range (Heater)
Allows to change the heater range. This should be set to 'auto' by checking the box next to the heater range menu.
[%] (Heater)
Current heater output in percent of the current range.
Meta Control
Enables/disables the Meta controller. This should be on.
Setpoint (Control)
The current setpoint of the (Lakeshore) temperature controller.

Tuning Parameters


PID values for the 0.5 [W], 5 [W] and 50 [W] settings at the DetectorTempController.

The parameters of the PID loop (Lakeshore 340) depend on the power range that the controller is using. Typically the cooldown requires the highest setting (50 W) and the 0.5 W setting is used to keep the detector at its operating temerature (80 K).
The FourStar software has proper defaults for each heater range.

Temperature Monitors

There are 16 temperature sensors inside the FourStar dewar. Sensors 1..8 are at the BackEnd near the LN2-tanks and sensors 9..16 (FrontEnd) on the 200K-shield and the optics barrel.

Channel LakeShore-1 (Backend) LakeShore-2 (Frontend) LakeShore-3 (Tank)
Control Detector Optics Tank (warmup only)
1 (9) Shroud Dewar Rad.Shield near Clamp n/a
2 (10) Detector Dewar Radiation Shield n/a
3 (11) Radiation Shield Radiation Shield n/a
4 (12) Rad.Shield near Clamp floating n/a
5 (13) Outer Detector Box Camera Module (back) n/a
6 (14) Inner Box Camera Module (middle) n/a
7 (15) FFW Cover Camera Module (front) n/a
8 (16) Detector Dewar Spare n/a 

TODO: scan diagram with sensor positions
Channel
Channel number (see diagram above) and graph color.
Temp [K]
Current temperature in deg. Kelvin.
Grad [K/min]
Temperature change in deg/minute.
Monitor
Enable/disable this channel.

Lakeshore Settings

Must be set via the front panel of the controller.
Setting LakeShore-1 (Backend) LakeShore-2 (Frontend) LakeShore-3 (Tank)
Resistor 50 [Ohm] 25 [Ohm] 12 [Ohm]
Max.Current 1 [A] 1 [A] 2 [A]

LN2 Process Controller

FourStar has an LN2 auto-fill system implemented with a JackRabbit micro-controller. The JackRabbit controller is programmed in a 'C' like language, that allows realtime operation using cooperative multi-threading. It monitors a variety of sensors and displays their readings on an LCD screen attached to the controller. The FourStar GUI retrives the LN2 and sensor data via the network and displays them on the 'LN2+Sensor' window (see Fig. 5).
The LN2 fill system runs independently of the FourStar control software and fills the shroud dewar by monitoring a capacitive level sensor. It can open the tank valve via a solenoid at a programmable LN2 level (eg. 10%) and closes the valve when the level reaches the 'full' level (eg. 95%).
This micro-controller also monitors the vacuum by digitizing the output voltage of a 'Pfeiffer' vacuum gauge and analyzing the current created by the ion-pump (model?). It also monitors six temperature sensors on the outside of the vacuum vessel and four temperature sensors located inside the eletronics racks.
The LN2+Sensors main menu contains the following menu entries:
Show LevelGraph
Opens the LN2-level graph showing both tank levels.
Show PressureGraph
Opens the pressure graph (Pfeiffer gauge).
Show TempGraph
Opens the temperature graph for the 10 environmental temperatures.
Edit GraphPars
Opens a dialog box that allows to edit the graph parameters.
Create PDF
Creates a PDF-file of the active (foreground) graph.
Edit Fill-Parameters
Opens a dialog box that allows to edit the LN2 fill system parameters.
Re-Open Connection
Recover the communication to the LN2-Process-Controller
Lock/Unlock GUI
Lock (or unlock) the editable fields LN2+Sensors GUI.

Shroud LN2-Level
Displays the current fill-level (by volume-%) of the outer (shroud) dewar.
Inner LN2-Level
Displays the current fill-level (by volume-%) if the inner (detector) dewar.
Mode (Control)
Set the auto-fill system control mode
  • PassThrough: Off
  • DeadReckoning: Use the hold-time and fill-time parameters of the LN2 fill system parameters dialog.
  • Automatic: Use the level sensor of the shroud dewar and the near-empty parameter to initiate the filling of the tank.
    • Status
    Update the fill-levels, pressure-sensor(s) and the process controller status (solenoid, alarm, etc).
    Solenoid
    Manual solenoid control.
    SineWave
    Enable/disable the sinewave signal used by the fill-level sensor. This might be necessary, if this signal interferes with the detector readout.
    DewarVacuum
    Current pressure gauge (Pfeiffer) readout.
    Temperatures
    Various temperature sensors along the outside of the dewar and inside the electronics racks.
    Predicted Tel.Focus
    Calculated focus value from the environmental temperature sensors on the outside of the dewar (currently unused).

    Auto Fill System

    The auto-fill system has three levels: LN2-Processor Parameters

    Graphs

    The FourStar control software uploads the current system status every 5 minutes to a computer located in Pasadena where a 'cron' script updates a web-page ( http://obs.carnegiescience.edu/instrumentation/FourStar/Status/fsstatus.html) showing plots of the most important sensor readings. The control software automatically creates 'alert' emails if any sensor (eg. pressure or temperature) indicates a problem. These emails are sent to the local (LCO) staff and to the FourStar team in Pasadena. 

    TODO:  graph examples

    Graph Parameters

    TODO: edit graph parameters

    2009-04-20, Christoph C. Birk, Carnegie Observatories