Fridge Manual and Monitoring
- The Fridge Control
- How the fridge works
- Using the fridge
- Fridge Cabling Setup
- Fridge Power Supply
- Operating the Power
- Controlling the
- Controlling the
supplies from the DAS computer
- Recovering from
Running Out of LHe
- Mucking with the AUX Fridge Board
- Enabling/Disabling the Array and IC
- Replacing the AUX Board with the
Array GRT Jumper Cable
- Putting Bolocam to Sleep
- Sleep Procedure
- Waking up Bolocam
- Revision History
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The Fridge Control
How the fridge works
The Bolocam refrigerator actually consists of 3 closed-cycle helium
The UltraCooler (UC) consists of a 3He closed-cycle fridge that cools
the focal plane itself. The InterCooler (IC) consists of both a
4He and 3He close-cycle fridge that cool a buffer stage that lies,
thermally, between the 4K LHe bath and the focal plane; the IC thus
intercepts most of the heat load from 4K. The UC is optimized for
low temperature at the expense of pumping speed; the IC is optimized
pumping speed at the expense of base temperature. During
operation, liquid 3He is condensed in both the UC and IC stills and is
pumped on by the respective charcoal pumps. There is no 4He
pumping during quiescent operation.
The cycling of the refrigerator is a somewhat complicated
procedure. The trick is that, to condense 3He, it is necessary to
provide a condensation point that is below about 2K in
temperature. Thus, a 3He refrigerator cannot be cycled directly
when mounted to an ambient pressure (4K) LHe bath. However, 4He
can be condensed at 4K (as is probably obvious), so a 4He closed-cycle
refrigerator is used to cool the 3He condensation point(s) to about 1K,
then the 3He refrigerators can be started.
During this procedure, connections between the pumps and the 4K bath
must be broken and remade. For the UC pump, this is done with a
passive, weak thermal link. For the IC pumps, the
connection is made by gas-gap heat switches, called the IC 4He and IC
3He heat switches. A gas-gap heat switch is just a long tube with
a reentrant shaft that
is connected to a charcoal pump. When the pump is heated, He gas
in the pump is evaporated into the tube and heat can be conducted
between the ends of the tube. When the pump is allowed to cool
back to 4K, the pump adsorbs all the gas and the conduction is
The fridge cycle goes as follows:
- The IC 4He heat switch (HS) heater is turned off. This
thermally disconnects the IC 4He pump from the 4K bath so it can be
- The IC 4He pump heater is turned on. This causes the 4He
adsorbed in the charcoal pump to evaporate. The 4He is cooled to
4K by the 4K condensation point (a point along the IC 4He pump tube
that is well connected to the 4K bath), condenses, and drips into the
- Once a sufficient amount of 4He has been condensed, the IC 4He
pump heater is turned off and the IC 4He HS heater is turned on.
This causes the pump to cool so that it begins to adsorb 4He from the
still; i.e., it begins to pump on the 4He in the IC 4He still.
The UC 3He condensation point is a connection between the IC 4He still
and the UC 3He pump tube, about midway up the tube, while the IC3He
still is in the same block of copper as the IC 4He still. Thus,
on the IC 4He still cools these points to about 1K.
- The IC 3He pump heater is turned on and its gas-gap heat switch
is turned off, causing the pump to heat up and the 3He in the 3He pump
charcoal to desorb. This gas is cooled in the IC 3He still where
it is in thermal contact with the IC 4He still. The IC 4He and IC
3He stills are actually made from the same
piece of copper; the liquids do not mix, but the two stills are in
direct thermal contact. Thus, the IC 3He gas is cooled to below
its condensation temperature in the IC 3He still itself. This
direct contact allows condensation of much more 3He than is condensed
during the UC cycle later; the larger 3He liquid volume is needed due
much larger heat load on the IC.
- Midway through the IC 3He cycle, the UC pump heater is turned on,
causing the UC pump to heat up
and 3He in the UC pump charcoal to desorb. The UC 3He is cooled
by the UC 3He condensation point that is in contact with the IC 4He
still, causing the UC 3He to condense and drip into the UC still.
- Once a sufficient amount of 3He has been condensed, in both
stills, both pump heaters are turned off. The IC3He gas-gap heat
switch is turned on to cool the IC 3He pump. The UC pump passive
heat link pulls the UC
down to 4K. The cooling of the two pumps allows them to begin
pumping on their respective stills. The IC4He pump heat switch is
turned off at this point, too.
- Once the IC 3He cycle is finished and the IC 3He still cools to
its base temperature of about 350-400 mK, the heat load on the UC is
reduced tremendously and it cools to its base temperature of about 265
- Once the IC 3He cycle is done, the quiescent state is:
One must exercise careful control over how much 4He is condensed during
the IC4He cycle.
The goal is to have condensed enough 4He so that the 4He runs out just
as one has condensed all of the 3He in the IC 3He and UC stills.
If too much 4He is condensed, then it will remain when the 3He pumping
begins. The 4He has a large heat capacity and will prevent the
IC 3He still from cooling to its nominal base temperature. If too
little 4He is condensed, then not enough 3He will be condensed and the
UC and IC 3He hold times will be too short.
- All pump heaters off
- UC pump coupled to 4K bath by UC heat link (passive)
- IC 3He pump coupled to 4K bath by IC 3He heat switch (heat
switch heater is powered)
- IC 4He pump and heat switch heaters off
Here is a picture of a successful fridge cycle; note the cycling of the
pump and heat switch temperatures. There is a 3.5 hour delay
period at the start, as indicted by the Time Delay control. Click
on the picture to get a
larger copy. Note the logarithmic vertical scales. The IC
GRT has a voltage offset that makes it untrustworthy above about 700
mK; it isn't really sitting at 800 mK for that extended amount of time,
it was warm.
Using the fridge
The fridge control program provides both generic temperature monitoring
as well as runs a program to cycle the refrigerator. The program
consists of setting various heater voltages and currents via the fridge
heater power supplies in the sequence indicated above for specific
amounts of time. The temperature monitoring runs independently of
the fridge control.
Loading and starting the program
Using the startup fridge program startFRIDGE
Note that at each steps, the user can just cancel its action by
clicking the 'cancel' button.
- Click on the icon startFRIDGE
available from the Desktop. Upon execution, labview will start (if not
already in memory) and the Bolocam Fridge Control Startup program will
start by poping up a window. From this window, select the operation you
wish to do: Cycle, Cooldown,
Warmup, or Temp from the menu ring. The main reason to
differentiate these actions are (i) to automatically generate
appropriate filenames, (ii) assign appropriate Y-scales for the
temperature graphs, and (iii) to start or not start a delayed cycle.
Also, in this pop-up window, the Startup program automatically assigns
the per default directory D:\fridge_data\
in which the log files will be stored. Note that the user can choose to
select another directory by clicking the change button. Click OK when
your choices are made.
- If a cycle has been selected, a second popup window will replace
the first one in which you can enter the delay (in HH:MM) before the
cycle will actually start. This window also act as a reminder of the
imperative steps to perform in order to ensure a perfect cycle i.e.:
- Disconnect the IC and Array diodes on the auxiliary
thermometry (AUX) board
- Tilt the cryostat (ZA=55) if its mounted on the telescope, or
to the line on the dolly (going right when facing the cryostat and the
Using the old-looking but highly reliable vi (been used for years)
The latest version is fridge_cyle_20040513.vi
and can be found in C:\documents
and Settings\Bolocam\My Documents\Labview vi\FRIDGE .
Before starting the program running, you must:
After setting the above, hit the arrow in the upper left corner of the
screen to start the program. The temperature displays should
immediately show some nonzero reading. The data collection rate
is set by a control at the top of the screen.
- Give the name of a data file to write the temperature log
information to. The data should be written to the directory D:\FRIDGE_DATA. The
default file is D:\FRIDGE_DATA\tempdata.txt.
When cycling the fridge, we usually use a filename like cycle_YYYYMMDD.txt where YYYYMMDD is the date of the
- Set the big button on the left to DISABLED or ENABLED depending on whether
you want to cycle the refrigerator or just run the temperature
- If you want to delay the fridge cycle, set the time delay
control. The fridge cycle takes about 2 hours, and roughly 1 more
hour is required for the system to fully equilibrate.
Starting and viewing the web server
An image of the screen is accessible via the web at http://andante.submm.caltech.edu:8080/Fridge_cycle.html.
This link is available on the main Bolocam
web page also. The screen shot only shows the visible part of
the front panel, so make sure you leave the front panel viewing the
thermometry displays! If the web page is not working, or you want
to to turn it on, do the following:
- Go to the menu bar and select Tools
-> Web Publishing Tool
- You should see a dialog box with document title Fridge_cycle, VI name Fridge_cycle.vi, and the viewing option should be embedded.
- At the bottom-center of the dialog window, click on the Start Web Server button.
Explanation of thermometry
Some explanation of the thermometry is in order:
- IC 4He pump, IC 3He pump, UC pump: temperatures of the
pumps. These are hot when He is being desorbed from the pumps.
- IC 4He HS, IC 3He HS: temperatures of the charcoal of the heat
switches. When these are hot, the heat switch conducts heat.
- IC Heat Exchanger: the temperature of the IC heat exchanger,
which is about midway between the IC pumps and the IC stills
- 77K and 120K diodes: these are temperatures of sections of the
JFET stage, they nominally run at something like 85K and 135K,
respectively, during normal operation.
- 4K plate diode: temperature of the 4K bath
- IC diode, Array diode: diode thermometers on the focal plane cold
stage. These are usually disconnected during normal fridge
operation (they dissipate too much power), so they usually read
nonsense. Used primarily during cooldown and warmup.
- Fridge Base: this thermometer is not in use, should read nonsense
- UC and IC Fridge GRT: these are the germanium resistance
thermometers on the UC and IC stills. They are calibrated to be
accurate when the stills are operating near their base
temperatures. These are not incredibly accurate readouts (trust
them to no better than a few mK), but they should at least behave
Getting more control of the cycle (for experts only!)
If you scroll right, you can see some of the machinery and how to get
more control of the cycle (double-click to get a bigger version):
Some additional items that are probably only of interest to experts are:
- The cycle program itself is just a text file with heater current
and voltage settings. The name of the file is specified in a
control at the upper left of the second half of the front-panel
screen. A default program, cycle_standard.txt,
is used to do the standard cycle. If you want to modify the
cycle, you can just create a new program file and enter it in the
- The program that is read in is displayed in the large matrix in
the center of the second screen.
- The program line being currently executed is shown below the
- The current heater voltages and currents are displayed just above
the fridge control program.
- UC and IC GRT range settings: the fridge thermometry board has
two current settings for the GRTs. Normally, they are on the low
current setting, appropriate for the highest resistances. If you
for some reason want to read them out while they are warm (low
resistance), flip the current setting switches on the board front panel
and modify the range settings here as necessary.
- The UC and IC GRT calibration curves (Chebyshev polynomial fits)
are shown. They should not be modified unless you know what you
- Next to the calibration coefficients are some indicators showing
the state of communication with the fridge power supplies.
- Also next to the calibration coefficients is a toggle switch that
lets you put the fridge control in test
mode. In this mode, the time settings in the fridge
program file are ignored and each setting is held for 12 seconds.
This lets you test a new program quickly. Don't forget to flip it
to its off state before
starting a real fridge cycle!
- Near the test mode switch is a control for the "Fridge PSU GPIB
Lock wait time constant". Since both the monitoring and control
subroutines of the program access the fridge heater power supplies, a
locking procedure is used to prevent access conflicts. This
control indicates the amount of time to wait between checks for the
lock being free.
- At the top of the second screen are GPIB addresses and PSU
channel numbers for the various fridge heater supplies. You would
only need to change these if you switched which supplies were used for
- The remainder of the indicators are ancillary variables needed to
make the history displays; you likely will never need to worry about
Fridge Cabling Setup
Here is a schematic of the fridge cabling (click on the picture to get
a larger version):
See the picture
of the rack containing the heater
supplies and white breakout box.
- Connect fridge rack power supply to e-box power supply input
connector using triple-banana-to-DB15 female cable. This is the
same supply that will power the lockins. See the picture.
- Red = +18V, black = -18V, green = GND. The PSU actually
two independent supplies. We use the right one to generate +18V
tying its negative end to the PSU chassis ground (the banana jack with
the green coloring) and the other to generate -18V by tying its
positive end to the PSU chassis. For good measure, we tie the two
chassis banana jacks together, and tie this to the rack itself using a
banana cable with a lug on one end.
- Clean/Dirty: it would actually be good to run the PSU from the
power on the telescope itself and the computer from dirty power (any
plug). To date, we've run the computer and the PSU off clean
That's probably bad. But separate grounds could be bad also in
the fridge monitor voltages may get some 60Hz pickup (though,
nominally, the ADC card in the computer has differential inputs).
experimentation will be necessary. The day crew can advise as to
jacks are clean power.
- Connect up DAS computer, monitor, mouse, keyboard
- Connect white breakout box to the DAS computer via 100-pin
cable, connects to port on back side of white breakout box (yes, the
connection is a bit flimsy).
- Connect the white breakout box to the dewar e-box via two DB50
female cables (feel free to use DB50 male-DB50 female cables to extend
the cables if necessary). The connector ports are on the back of
the white breakout box, toward the left side of the box when you are
looking at the back. The leftmost connector (labeled fridge or something like that) is
for the cable labeled FRIDGE;
the port just to the right of the first one (labeled thermometry or something like that)
is for the cable labeled AUX.
There is an unlabeled D connector at the right side of the back of the
white breakout box, ignore it. At the e-box, the FRIDGE cable goes to the leftmost
output connector on the e-box when looking at box from the back side
and the AUX cable goes to the
rightmost output connector.
- Connect fridge
supplies (Tektronix boxes):
- to DAS computer via GPIB cables
- to fridge via BNCs to white breakout box. There are 6
outputs, as described below. Five
of them are explicitly labeled, the sixth is the JFET heater
supply. There are similarly labeled BNCs on the white breakout
box , so just connect them up one-by-one. Some lines have
duplicate BNCs. These are backups. Be careful, though, some
are not wired! You can test whether you are connected to
something by trying to supply current or voltage to the each heater,
Fridge Power Supply
The heaters on the fridge are powered from the fridge
power supplies, the two
Tektronix supplies with blue-green cases sitting in the fridge
rack. Each supply has three outputs. The first two (the
leftmost two) are low current/high voltage (36V/1.5A). The third
one is high current/low voltage (6V/3A). The first two outputs of
the two supplies
are used to run the UC pump heater, the IC3He pump heater, the IC4He
pump heater, and the JFET heater; all of these heaters have resistances
of hundreds of ohms and thus require relatively high voltages at
typical currents of 50-100 mA. The other outputs are used to run
the heat switch heaters, which
are 10 kΩ heaters and only need 5-6 V and less than 1 mA.
Identifying the parts of the supplies (see the closeup):
The outputs of these power supplies go to BNC connectors on the front
of the white breakout box (a 19"-rack-width box) in the fridge
rack. This box converts to the DB50 cables that go off to the
- The output jacks are the pairs of red/black banana jacks,
labelled 1, 2, and 3 from left to right. The green banana jack is
a chassis ground jack and can be ignored.
- The CURRENT and VOLTAGE displays are at the top.
- There is a matrix of status lights in the upper right of the
- The 12 buttons above the output jacks control whether the front
panel is enabled, which channel is displayed, whether the outputs are
on or off, etc.The 16 buttons on the right side are used to set
currents and voltages. Note the button that has a bent arrow on
it; this is the ENTER button.
Operating the Power
- For the pump and JFET heaters, we set the voltage to 35 V as the
limiter in all cases and then control the current directly (either
manually or via the fridge control program).
- For the heat switch heaters, it is opposite to the above: we set
the current to 2 mA as the limiter in all cases and then control the
- The fridge program has been modified (April, 2004) to set the
limiters prior to starting the fridge cycle. So you don't need to
worry about setting these ahead of time.
These are the
"nominal" settings for the supplies, when you don't want any of the
heaters on. Do this with
the outputs OFF
so that you
can see the limits, not the actual values. Once you have made the
settings, you should hit the OUTPUT
button to turn the outputs ON
It's actually not too important to set these nominal values anymore; as
of April, 2004, the fridge control program initializes all the supplies
(except the JFET supply) as necessary at the start of the cycle.
- JFET heater: current has been set by someone knowledgable, don't
touch it, it is 0.010 A for October 2003.
Voltage should be set
to 35 V.
- UC pump heater: 0 A, 35 V
- IC3He HS heater: 0.002 A. If the fridge is currently cold
and you want to keep it cold until the cycle starts, then set the
voltage to 5V. If the fridge is out, or you don't care if you
keep the fridge cold, you can set this to 0V.
- IC4He pump heater: 0 A, 35 V
- IC3He pump heater: 0 A, 35 V
- IC4He HS heater: 0.002 A, 0 V
If you want to control the PSUs manually, here is the information you
need. See the picture to
identify the buttons.
front panel control:
button makes it possible to control the supply using the front panel;
if the supply is not in LOCAL
mode, the front panel is locked out and the supply is controlled by
GPIB. You can feel free to press the LOCAL
button at any time, even
during a fridge cycle -- the fridge computer can still control the
supplies. If the
power supplies do not appear to be responding even after pressing the LOCAL
button, it may be because the fridge_cycle
program is simultaneously trying to read them. Set the sample
rate on fridge_cycle
relatively large value (less than 1 per minute) and then attempt to
program the supplies. Set the sample rate for fridge_cycle
back to its original value afterward.
There is an OUTPUT
button that enables/disables
the outputs. The OUTPUT
button controls relays that actually connect the internal
supplies to the output banana jacks. Thus, even if you have set
the output currents and voltages, they won't actually be activated
until the OUTPUT
been pressed. Conversely, if the output currents and or voltages
are set to 0, then pressing the OUTPUT
button will not do anything except energize the relay; current will not
necessarily flow. On the display, in the upper right corner,
there is an OUT
will be on if the outputs are enabled (1st row, 4th column in matrix of
select which channel is displayed:
To set which
output is displayed/controlled via the keypad: find the keys that say OUT1
in light blue above them.
Press the SHIFT
then press whichever of these buttons corresponds to the output you
want to display/control. Note that the supply must be in LOCAL
mode for these (or any other)
buttons to work. The first column of the matrix of status lights
has three lights indicating which supply is being displayed.
How the displays work:
The displays do
different things depending on what state the supply is in. When
the outputs are off (OUT
off), then the displayed current and voltage are the values that have
been set (see To set outputs currents and
below). When the outputs are on (OUT
light on), then what is shown
is the actual current and voltage. What these are depends on the
settings. Though you set a current and a voltage, the supply
can't necessarily satisfy both of these settings. It picks the
"lower" one. For example, if you set 50 mA and 35 V for the UC
pump heater, which has a total resistance (including leads) of maybe
250 ohms, then you will see 0.050 A and 12.5 V on the display because
50 mA x 250 ohms = 12.5 V < 35 V. The current and voltage
settings thus act in some sense as limits for each other.
To set output currents and voltages:
- Select the output you want.
- On the numeric keypad are CURRENT
SET and VOLTS SET
buttons. Press the one you want.
- Enter the value you want to set using the buttons, e.g., for 35
mA, hit 0 . 0 3 5 followed by
the enter button, which is an arrow with a right angle in it.
- What you see on the display will depend on whether the outputs or
on or off -- see How the displays work above.
supplies from the DAS computer
There is now a program for direct
control of the power supplies
available on the DAS computer. Go to the desktop of the DAS
open the shortcut to the FRIDGE
folder, and double-click on ManualPSUControl.
Hit the arrow in the upper left corner to start the program. The
bottom two rows of displays indicate the current power supply
settings. Set the middle two rows of controls to the desired
settings. Note that you must set all
the controls appropriately, even the ones you don't want to change;
when the program commands the power supplies, it sets all of the
control values. When you are ready to issue the command, press
button on the left side of the panel that says "Press to set PSU
values". The bottom two rows of displays should then update to
your new settings. If you have problems, press the Reset button
upper left and try setting the power supply values again.
Note that the current and voltage indicators show the actual currents and voltages, not
the programmed ones.
There may be interference of this program with the standard fridge
cycle program if they try to communicate simultaneously with the fridge
power supplies. To avoid such interference, set the fridge
control program to a slow sampling rate (1 per minute or slower) before starting ManualPSUControl,
and then do your manual commands in the interval between samplings by fridge_cycle,
and then stop ManualPSUControl.
If the programs seem to interfere (very slow reading of supply
settings, nonsense or mixed-up values), then just kill ManualPSUControl
using the red stop-sign button in the upper left of the screen and try
again. Note that the normal stop button on the front panel of ManualPSUControl
will not work if it is hung in the communication cycle.
Running Out of LHe
When you run out of LHe, everything warms up. If the array gets
too warm, the fridge cycle will fail because the array will not cool
enough to condense 3He in the UC still. So you have to cool the
array down by hand prior to starting the fridge cycle. To do
this, do the following:
You do not need to worry about the IC getting too warm.
There is a passive heat switch connecting the IC to the 4K bath, so the
IC cools off automatically once the LHe bath has been refilled.
The IC cools off much more quickly than the UC does, so getting the UC
cold assures that the IC has also gotten cold.
- Set the UC pump heater to 35 mA current (should already be set to
35 V voltage).
- The UC pump will heat up and you will see the array GRT (the
thermometer read out by the LR750 resistance bridge on the 3rd floor)
cool down. There is a calibration curve for this GRT ("UC
optics") in the big black Bolocam binder.
- Get the array below 10K, then shut off the UC pump heater.
- Wait until the UC pump has cooled down below10K (so all the gas
has been sucked back into the pump).
- Confirm that the array is below 10K by checking the resistance
bridge reading (in fact, it should have cooled further when you shut
the UC pump off).
- Prior to starting the fridge cycle, check that the supplies are
back on their nominal
- Start the fridge cycle as indicated on the Daily
Observing Tasks page.
Mucking with the AUX
The AUX fridge board reads out a number of diode thermometers and
provides access to the array GRT and heater. During cooldown to
4K, the array and IC diodes are read out using this board. Before
cycling the fridge, however, it is necessary to disable these diodes
because they dissipate too much power. Alternately, when Bolocam
is set up for regular observing, the AUX board is completely removed
and a jumper cable used to allow access to the array GRT only.
Here are instructions for making these changes.
the Array and IC Diodes
It is straightword to disconnect and reconnect the array and IC diode
readouts. These readouts are located on the AUX fridge board,
which is the rightmost board when viewing the boards (as in this picture, though note that the AUX board is
not in place in this picture -- it would go in the slot in which you
see the black-and-white jumper cable).
- Open the top of the E-box (if it is closed) and turn off the
power switch to the AUX board (all the way at one end of the set of
-- the switches are in the same order as the boards).
- Open the E-box and remove the board in the rightmost slot.
You will likely have to disconnect a cable going from the face of the
board to a feedthrough connector on the bottom of the E-box.
- The board will look like this (click on the picture for a larger
Notice the handwritten labels and the yellow jumpers. Readout of
a given diode is enabled or disabled by the appropriate yellow jumpers.
- Disconnect or reconnect the array and IC diode jumpers to match
one of these pictures (click for a larger version):
NEED BETTER FOCUSSED PICTURES!
There are two possible configurations for the jumpers:
The two different configurations
drive current through the diode in opposite directions. When
reconnecting the diodes, you may have to experiment with both
configurations to find the right one. A handy way to remember
which one is correct is to, when you disconnect the jumper, only
disconnect the right side connections, as demonstrated in the
"Disconnected" picture above; then, when someone comes to reconnect, he
only needs to reconnect the right side, for which there is only once
choice of how to do it.
- Replace the board in its slot and turn its power switch back
on. (If you are reinserting the board for the first time after
observing, remove the black-and-white jumper cable that is occupying
the slot. You will likely also see a black-and-white GRT cable
connected to the outside port of the feedthrough connector on the
bottom of the E-box that corresponds to this slot. Disconnect
that cable too.)
- Connect a long DB50F-DB50M cable from the top connector on the
face of the board to the corresponding feedthrough connector on the
bottom of the E-box.
- If it is not already connected, connect the AUX fridge monitor
DB50 thermometry cable to the same feedthrough port. This cable
will originate from the back side of the white thermometry breakout box.
- Check that you are now seeing reasonable temperature readings
from the 4K Diode, Array Diode, and IC Diode on the fridge monitoring
screen. If any of the diode readings are nonsense, the polarity
jumpers may need to be modified.
Replacing the AUX
Board with the Array GRT Jumper Cable
See the link to the
Putting Bolocam to
There are occasions where Bolocam will be on hiatus for a number of
nights, but then will come back into service. During such
periods, it is sensible to put Bolocam to "sleep" to minimize cryogen
Putting Bolocam to sleep is easy:
- Restart the AUX fridge readout electronics as instructed above,
with the Array and IC diodes enabled. Make sure you have
reasonable thermometry readings for the 4K Diode, Array Diode, IC
Diode, and all the pumps and heat switches.
- Turn off power to all the boards in the E-box except the two end
boards, which are the thermometry boards. This turns off power to
- Allow the LHe to run out.
- Monitor all the diode thermometers during the sleep period.
The 77K and 120K diodes should cool because the JFETs are off.
The remaining diodes will all slowly warm after the LHe has run out.
- If the LHe layer diodes (4K, Array, IC, pumps and heat switches)
approach 80K, you need to keep them from warming further as follows:
Maintain until you need to wake up Bolocam.
- If you are sleeping for a short period (a few days), you can
just put a little LHe in to recool everything, and then let it
rewarm. The 4K diode will return to 4K with only a little bit of
- If you are sleeping for longer than a few days, the simplest
thing is to put LN in the LHe bath. You don't need very much --
1-2 inches on the LN dipstick in the bath -- because the heat load on
the LHe bath is very small.
Waking up Bolocam
You need to plan ahead here to ensure Bolocam is fully recooled in time
for your observing, as well as to ensure the JFETs have had time to
reheat to their nominal temperature. The array takes the longest
time to cool, so the time needed is set by how warm the array is.
Typically, one will have let the array warm to about 80K and then hold
it there by LN or LHe in the LHe bath. From 80K, it takes about
15 hrs to recool the array to 4K. The procedure for recooling is
the same as for the normal LHe cooldown, see those instructions elsewhere.
Don't forget to also use the JFET heater to quickly heat the JFETs.
A reasonable schedule for the recool is to start the recool procedure 1
day before the day that Bolocam is needed again; e.g., if Bolocam's
night back on is a Wednesday, start the recool on Tuesday. The
recool can be started at the end of the day. Though note that the
first LHe fill may run out quickly, so one should fill with LHe 1-2 hrs
before the end of the day and then top of just prior to leaving.
You will still need to cycle the fridge after recooling the array to
4K, so make sure you leave time for that too.
You will have already turned the JFETs on during the JFET
heating. You may turn on the remainder of the electronics boards
whenever you like. Prior to observing, you will have to remove
the AUX board, reinstall the array GRT jumper cable, and connect the
array GRT to the resistance bridge; how to do this is explained elsewhere.
- 2003/11/09 SG
- 2003/11/11 SG
More specific instructions for IC3He HS setting prior to
- 2004/01/14 SG
Add instructions for setting up supplies and cabling
- 2004/01/29 SG
Add links to get back to main pages.
- 2004/04/20 SG
Correct some misdirected links.
- 2004/04/24 SG
Significant additions, especially details on operation and cycling of
the refrigerator. Troubleshooting interference between manual
setting of PSUs and reads by fridge_cycle program.
- 2004/05/13 SG
Update for simultaneous IC 3He / UC fridge cycle, new position of
- 2004/10/02 SG
Add anchor for example fridge cycle so it can be linked to from
- 2005/03/08 SG
Update instructions for starting web interface, add section subheadings
in various places.
- 2005/06/03 SG
Add detailed instructions for array and IC diode jumpers on AUX
thermometry board, link to instructions for replacing AUX thermometry
board with array GRT jumper, and sleeping/wakeup instructions.
- 2005/09/11 PR
Updated instruction for new startFRIDGE and automated vi. Update fridge
PS/Therm breakout box pics.
- 2007/07/30 SG
Update links to fridge snapshot page.
Contact the Bolocam support person.