Electronics Setup and Cabling

  1. Mounting and Powering up the Electronics Backpack (a.k.a., the E-Box)
    1. Mounting and Cabling:
    2. Powering up:
  2. Mounting up the Lockins, DAS, and Associated Electronics
  3. Cabling!
    1. Signal cabling in the e-box
    2. from the e-box to rest of world
    3. from lockins to DAS
    4. auxiliary cabling
    5. power cabling at DAS rack
    6. AC power and grounding
  4. Configuration of the Bias Board(s) for Various Modes
    1. Rev 2 Bias Board
    2. Rev 3 Bias Board
  5. Cabling for DC Bias Skydip IV Curves
  6. Revision History
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This page could stand some more pictures, but only experts will need them.

Mounting and Powering up the Electronics Backpack (a.k.a., the E-Box)

Mounting and Cabling:

  1. With the e-box on the ground, move all the Cable G's (the 55-pin-circular-to-DB50-and-DB9 cables) out of the way of the horseshoe-shaped slot on the bottom of the front part of the box.

  2. Get a set of screws ready for mounting the e-box to the dewar.  These should be found in the electronics box section of the dewar screw container.  They are just 8-32 socket heads.  Get a 9/64" ball driver ready.

  3. Lift up the e-box and align the horseshoe slot with the circular hermetic feedthroughs.  This can be done by one person but is much easier with two.  Make sure you don't catch anything under the e-box.

  4. Line up the screws and get a couple of the front-most (furthest from the rest of the box) screws in to carry the weight.  Don't tighten them.

  5. Get more screws in their threads.  You only need to put in every other screw.  Don't tighten until all the screws are in.  Then tighten them all down.

  6. Mate the circular connectors to the hermetic feedthroughs.  You have to be very careful to avoid damaging the hermetics:

  7. Check that the bias board spider cable (DB50 to 6xDB9) is well mated to the DB9s on the Cable G's.  Make sure all the jackscrews are tight -- those bias connections are very important!

  8. Connect up the power cable to a PSU as indicated on the Fridge page.

Powering up:

  1. Each switch near the DB50s on the Cable G side of the backpack corresponds to one slot in the rack and has a LED to indicate it is on.  Note that the bias board is double-wide and so one switch is not used.

  2. Each preamp should draw about 300 mA from both the + and - supplies.

  3. The bias board draws about 250 mA from each supply when not connected to the JFETs, about 300 mA when connected.

  4. The thermometry boards draw a total of about 50-60 mA together, more for the fridge board.

  5. Beware of any readings taken without both the bias board and the preamps on.  The preamps can load the JFETs if they are not turned on, which results in funny current flows from the bias board.

  6. Make sure all front panel switches on the fridge and auxiliary thermometry boards are in the HIGH R state; if they are in the LOW R state, the fridge monitor readout will be wrong and the boards may overheat the fridge.

Mounting up the Lockins, DAS, and Associated Electronics

We have two black shipping racks that house the lockins, the DAS, the resistance bridge that reads out the focal plane thermometery, and other associated electronics.  Mounting all of this up is straightforward.  We include pictures of the
lockin rack and the DAS rack to illustrate.  Note how the more sensitive analog equipment (lockins and resistance bridge) sit in the lockin rack and the digital equipment (multiplexers/SCXI chassis, opto-isolator board, DAS computer) sit in the DAS rack.  The power distribution panel in the lockin rack accepts the same kind of DB15 power cable that is used to power the dewar e-box.  The PSU chassis is grounded to the DAS rack and the DAS and lockin racks are tied together.

See the section on AC power and grounding for details about connecting the PSU.


Signal cabling in the e-box

from the e-box to rest of world

from lockins to DAS

auxiliary cabling

power cabling at DAS rack

AC power and grounding

(we leave this until last because it is the most complicated aspect!)

For observing, all power should be taken from the telescope outlets, not the dome.  Use extension cords to bring telescope clean and dirty power to the third floor.  The day crew can advise as to which outlets are clean and which are dirty power. 

Configuration of the Bias Board(s) for Various Modes

Rev 2 Bias Board

Here is a picture of the board.

For all modes, the FIXED/VAR switch should always be in VAR mode and the uppermost 6 potentiometers should always be full clockwise.  The FIXED mode disables the gross adjust potentiometers and sends a fixed (incorrect) bias into the dewar.

Adjustable DC bias mode:
Triangle-Wave DC bias mode:
Adjustable AC bias mode:
Triangle-Wave AC bias mode:

Rev 3 Bias Board

Here is a picture of the board.

Again, the upper 6 potentiometers should always be full clockwise and locked.

The AC/DC switch functions as on the Rev. 2 board.

The VAR/FIXED switch inserts a voltage divider in the bias generation path.  That is, it does not do what the label indicates.  If you find that you can't get voltages into the dewar as big as you expect (too small by a factor 10), this switch is probably in the WRONG position and is dividing the bias when you don't want it to.

The INT/EXT switch should always be in EXT mode.  The rotary switch knob takes the place of the the INT/EXT switch on the Rev. 2 board, essentially.

Adjustable DC bias mode:
Triangle-Wave DC bias mode:
Adjustable AC bias mode:
Triangle-Wave AC bias mode:

Cabling for DC Bias Skydip IV Curves

Typically, we want to take a skydip with IV curves in DC bias mode once or twice a run because the analysis of IV curves taken in AC bias mode is not entirely trustworthy.  We have to set up the cabling, though, so that the data look like the AC bias skydip IV curves to use the same analysis software.  This takes about 30 minutes, so plan accordingly.  The details depend on which bias board you are using, see above for more details on the bias boards.  Here are the instructions:
  1. Replace short cables inside E-box (from preamp outputs to RF feedthroughs) with long cables, connecting the long cables to the DC (top) outputs of the preamps; the short cables were connected to the AC (bottom) outputs.  You should find these longer cables in the 3rd floor Bolocam storage room.

  2. Disconnect the lockin-to-DAS cables for the DC LOCKIN signals at the DAS end, leave them hanging there to maintain their order.  These are the cables going into modules 2, 4, 6, 8, 10, and 12 (where the left-most module is module 1).

  3. Disconnect the monster preamp-to-lockin cables at the lockin input end and connect these directly to the DAS inputs that you just disconnected.  The cables should be attached in the following order:

    MUX  2: HEXTANT A 1
         4: HEXTANT F 2
         6          E 3
         8          D 4
        10          C 5
        12          B 6

  4. Set up kludge cabling for readout of bias monitor signals:

  5. If you are using a Rev. 2 bias board (the serial number on the front panel will be 2.X): Flip the CLOCK switch on the bias board RIGHT (to EXT) and make sure there is a shorting cap on the adjacent BNC.  See the diagram on the side of the e-box.  This shuts off the bias generator clock.

  6. Check that everything is basically working.  Start an IV curve going (see the instructions below to see how to put the board into DC bias triangle wave mode) and make sure you see signal on at least one channel in each hextant, the bias monitors, and the GRT on the DAS.  The channels to enter on the DAS screen for the various signals are:

    bolometers:     hex 1   DAS ch 32-55     (start at 32, )

                        2          96-119    (24 channels per hextant, each  )

                        3          160-183   (hextant offset by 64 = 2 x 32  )

                        4          224-247

                        5          288-311

                        6          352-375

    bias monitors:  hex 1    377    (yes, 377, not 376)

                        2    378

                        3    379

                        4    380

                        5    381

                        6    382

    RGRT: ch 56  = -(RGRT/200k)*10V

    Be especially sure that the hextant bias monitors and RGRT are being read correctlly; they are critical to the analysis.

  7. Adjust the DC bias setting to get the proper range for the IV curve.  With the INT/EXT switch in INT mode (internal DC bias, not triangle wave), adjust the bias so the bias monitors read about -6 V.  Then flip INT/EXT to EXT mode to get a triangle wave and confirm that the bias monitors peak at ~-9V.  If the bias monitors saturate (reach -10V) then reduce the bias setting as necessary.  Note that the IV curve always has a flat section at maximum bias; do not confuse this with saturating the digitizer.

  8. Turn the IV curve off:

  9. Run the BOLOCAM_SKYDIP_LOADCURVE macro as usual, but, if using a Rev. 2 bias board, exchange AC and DC everywhere the instructions tell you to flip the AC/DC switch.

  10. When you are done, go back to normal cabling/bias mode.

Revision History

Questions or comments? Contact the Bolocam support person.