The CRSP Reference Manual

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1. Introduction

This manual is intended as a guide to those support personnel who are involved with the installation, observing support, and troubleshooting of CRSP. It is not an operating manual for the instrument, and is complementary to the CRSP User's Manual in that it covers aspects of CRSP which are not of concern to the user. In addition, many of the procedures covered here, particularly with respect to troubleshooting, are potentially hazardous to the health of the instrument and should notbe attempted by visiting observers or casual users of CRSP.

2. Instrument Storage -- The Big Box

CRSP, rotator, and all associated knicknacks are intended for storage in a single large box. This box has wheels which permit it to be moved about (with some difficulty), and two steel bars across the top by which it may be lifted by crane hooks (one at each corner, outboard of the large nuts) or fork lift. One may also transport the box by fork lift from below, although care is required in inserting the forks. Unlike IRIM, the internal structure of CRSP is not supported by the cryogen fill necks, so there are no support tubes which must be inserted before transporting, but care should still be exercised to avoid excessive jarring of the instrument.

Main Compartment

CRSP sits on a hydraulic cart, with the four instrument "legs" fitting into guides on the cart table. Two of these have spring detents which lock the legs into place. THESE MUST BE LOCKED WHEN THE INSTRUMENT IS BEING ROLLED ABOUT, ESPECIALLY WITH THE ROTATOR INSTALLED. The instrument/rotator combination is topheavy, and it could tip over, with catastrophic consequences. The cart has a set of "elevated" wheels which fit into U-channel guides in the instrument box; when the cart is all the way in, it may be locked in place by two removable pins. In the initial preparation steps, CRSP is detached from the rotator and moved around separately on the cart; for installation on the telescope, CRSP and rotator are moved together. Detailed steps will follow in the checklist.

Important -- Before the cart and CRSP are rolled into the box, the cart must be in the FULL DOWN position, and the window cover must be removed from CRSP.

Drawers and Cabinet

The box has a built-in cabinet, a large sliding drawer, and four small sliding drawers for housing associated paraphernalia. Each of these is marked as to the contents. The top two small drawers contain the tools and alignment pins for installing CRSP. The third drawer contains antistatic gear for use if the electronics must be disconnected, as well as spectral calibration lamps.

The cabinet is used to store the ~ 12-foot cable wrapup connecting the instrument to the Cassegrain J-box when the instrument is shipped downtown. Two cables provide power to the instrument, while the third is a bundle of six fiber optic cables. THE FIBER OPTIC CABLES MUST BE TREATED WITH CARE. When installed, they should be secured to prevent strain or tight radius (< 7 cm) bending.

3. Installation Procedure

Although the mounting configurations of CRSP at the 2.1-m and 4-m telescopes are quite different, the general installation and removal procedures are similar. At the 2.1-m, the CRSP/rotator installs directly to the nominal gold guider; at the 4-m, the back focal position of the f/15 secondary requires that the CRSP/rotator mounts to the "white adapter" on its handling cart, with an additional guider (which is effectively a spacer) in between. The whole assembly is then installed on the 4-m guider using the elevator. At the 2.1-m, the guider should be installed with the TV mount to the South; CRSP should be installed with the fill tubes to the North. On the 4-m, it is necessary to install CRSP with the fill lines to the South for access from the cage door.

Fig. 1 Top View of CRSP

Fig. 2 Side View of CRSP

Fig. 3 Side View of CRSP, showing installation on Gold Guider

General Rules

For continued happiness and long life, there are a few useful rules which should be kept in mind when working with this instrument.

Pumpout and Precooling

When possible, this should be started the day before a scheduled block of observing time, since this permits adequate time for CRSP to precool. Starting the day of a run will result in late installation (at least 6 - 8 hours of precool are needed before filling with LHe), and dark current will be elevated during the first night due to slow cooling of some of the optics.

Telescope Installation

It will require several hours and about 50% or so of the LHe fill to cool the detector mount. During this time, CRSP may be reinstalled in the box and moved to the telescope dome, if it is not there already.


At the 2.1-m, the focal plane of CRSP is very close to the nominal telescope focus (5 cm behind guider), and the normal focus range of the guide probes is sufficient. The acquisition TV is used with a custom lens with a f/15 pupil stop to reject scattered moonlight.

At the 4-m, the f/15 focus is about 30 cm behind the f/8 focus, far beyond the range of travel of the guide probes or the acquisition TV. A 2000 mm focal length lens must be installed on the guide probe assembly to bring the f/15 beam to focus on the guide camera. A similar lens mounted in a long tube is installed on the acquisition TV to keep it within its nominal travel range. A secondary benefit is some demagnification and a consequent increased acquisition field.

Cable Installation

There are two sets of cables, a wrapup (3 cables) between the instrument and junction box, and individual cables (4) from the DCU to CRSP. They should all be in the instrument box.

Installing Counterweights

The electronics are sufficiently off center to require additional counterweights on the instrument to permit easy operation of the instrument rotator at large zenith angles. Two sets of weights, one on the cover of the ACU, the other above the LEDEX motors on the rotator, are sufficiently bulky that the instrument cannot be installed in the cart with the weights attached. The weights should be removed from CRSP when it is taken off the telescope and stored in one of the drawers in the cart; conversely, they should be installed after CRSP is put on the telescope.

Electronics Cooling

The WILDFIRE electronics generate sufficient heat that they must be actively cooled. The air vent fixture kept in the CRSP box should be installed on the left side of the DCU (Fig. 1, 3). The vent hose (at telescope where it exists) should be attached to this fixture and the vent fan turned on before powering up the electronics. Alternatively, one may attach a fan directly to the vent and exhaust the warm air into the dome at sites where the vent hose has not been effectively installed.

Balancing Telescope

Do your own thing, brah!

At the 2.1-m telescope, this may be a good time to install the "Christmas Lights" on the secondary and dress the cable so it can be accessed from the observing floor. These are used in aligning the instrument to the optical axis of the telescope.

At the 4-m, the Christmas Lights" are permanently installed on the f/15 secondary on swing arms and are usually left in place. The lights are accessed through the hatch on the side of the secondary cage. At both telescopes, a custom controller box powers the lights.

4. Getting Started

Most of this is covered exhaustively in the User's Manual, so only a brief outline is given here, except for the Twist & Shout procedure.

The CRSP instrument power supply is located in the computer room; with the switch on "remote", the power may be controlled by a small switchbox next to the observer's console.

Twist & Shout

As long as the detector is sufficiently cold to activate, this operation can be done in the afternoon. It need be done only before the first night of a block scheduled run, and if the previous run was on the same telescope, no actual adjustment may be necessary.

The purpose of T&S is to adjust the tilt of CRSP so its intrinsic optical axis is aligned with that of the telescope. This is effectively done when the detector can see all of the four "Christmas lights" at the periphery of the secondary mirror, and that lights on opposite sides give roughly the same signal. Because the lights may differ in intrinsic intensity, and illuminate the detector differently along and across the slit direction, it may not be possible to obtain equal signals for all four lights.

Fig. 4 Detail of tilt adjustment bolts on CRSP rotator.

Fig. 5 Images of all four alignment lights in balance.

Cryogen Refills

When all is well, the cryogen hold times for CRSP in powered up configuration should be > 18 hr for the LN2 and > 14 hr for the LHe. Filling at the beginning and ending of the night should be adequate.

Keeping a cryogen fill log and measuring the LHe level in the storage dewar once/day is good practice, as it can prevent duplicate fills and avoid unpleasant surprises.

5. Observing and Troubleshooting

The procedures for observing with CRSP are covered exhaustively in the CRSP User's Manual. For reference, proper values for status s and typical readouts for ?filter and ped are given at the end of this manual.

Troubleshooting is covered in Appendix III. An exception is the procedure for recovering from a limit switch activation, which is sufficiently critical to not be attempted by the observer without consultation with the instrument scientist.

Grating Limit Recovery

Activation of any of the three grating limit switches; short wavelength, long wavelength, or detent, immediately removes power to the grating motor to avoid driving the grating into a hard stop and possibly shearing the grating drive shaft. In the case of the long or short limits, the grating must be manually driven, using the knob on the grating drive motor, until it is backed out of the limit. It is imperative that the motor be turned in the correct direction to recover from these limits.

Short Limit Recovery

Symptoms are a "short lambda limit" error message in ?filter and a grating position readout < 100. To recover, turn the knob on the grating motor CLOCKWISE and verify that ?filter registers increasing grating positions. Continue until ?filter no longer gives a "short lambda limit" message. Normal motor control should then be possible.

Long Limit Recovery

Symptoms are a "long lambda limit" error message in ?filter. The grating encoder may read a value > 4000. To recover, turn the knob on the grating motor COUNTERCLOCKWISE and verify that ?filter registers decreasing grating positions. Continue until ?filter no longer gives a "long lambda limit" message. Normal motor control should then be possible.

Detent Limit Recovery

In theory, this limit should never activate, although it is remotely possible that one can change gratings without the detent engaging fully, with subsequent motion vibrating the grating out of its detent. The danger is that a partially rotated grating turret can impact the radiation shield before the short wavelength limit is reached. This problem is most likely to arise during a programmed motion; the symptom would be a shutoff of the motor during the motion and an ?filter reading of a grating position other than the programmed destination and a "detent" error message. Recovery is in two steps:

6. Removal (Deinstallation) of CRSP

In general, removal of CRSP may be accomplished by reversing the installation steps. Since time is usually an issue, many of the installation steps do not have to be undone; for example, one may simply remove CRSP and the rotator and install them in the box without removal of the cryogen fill tubes. Below is a short list of important items:

7. Useful Information

CRSP InSb Status Display
Detector Temp    = 1.099 Detector Htr Power (mw)   = 20.444
LN2 (cy7)    = 0.938 LHe (cy7)   = 3.103
Stage (cy7)    = 1.138   
VDet    = -3.038 VDDuc    = -3.624
Voff    = 0.444   
VDDout   : = -1.055 VGG    = -1.514
V3    = -2.686   
Data Offset 0    = -2.515 Data Offset 1    = -2.002

Typical ?filter Reply
% ?filter
The grating is at position 2580
The slit is at 380um (position 3)
The rotator is at position 2179
The filter is at j (position 4)
The limit switches are set to 0x008
  Grating number 1 is in the beam

Typical ped Display
Alpha Nuti g1 K 2.280 microns 600s
CRSP 2.1-m 29 Feb 1939 Charfman

Temperature Sensor Calibrations

There are three types of temperature sensors in CRSP, all of which operate on the principle of a temperature-dependent electrical resistance. These sensors are biased with a constant current (10 A) and the resultant voltage is read and displayed in the Instrument Status window.

The LN2 sensor is a 1n914 diode which has a relatively linear temperature/resistance relation from 50 - 300 K. The sensor in CRSP apparently has a voltage offset, so the values in the table should not be used to reference any other instrument.

The Detector sensor is a DT470 diode which has been individually calibrated by Lakeshore over the temperature range 10 - 340 K.

The LHe sensor is a 5.1 K Allen-Bradley resistor which has an exponential resistance/temperature behavior at low temperatures. It serves as an "empty" warning indicator for the LHe flask, since exhaustion of the LHe will cause the resistance to drop precipitously.

CRSP Temperature Sensors
Detector LN2 LHe
V T(K) V T(K) V T(K)
0.584 273 0.40 273 4.50 4.0
0.900 136 0.60 197 3.10 4.5
0.940 117 0.70 162 2.70 5.0
0.980 98 0.80 126 1.50 6.0
1.000 88 0.85 107 1.05 7.0
1.020 77.4 0.90 88 0.82 8.0
1.030 72 0.91 85 0.65 9.0
1.040 67 0.92 81 0.56 10.0
1.050 61.5 0.93 77 0.31 15.0
1.060 56 0.94 73 0.22 20.0
1.070 50 0.95 69 0.16 30.0
1.080 44 0.96 65    
1.090 39 0.97 61    
1.095 36 0.98 57    
1.100 33 0.99 53    
1.105 31 1.00 48    
1.110 28.8 1.05 33    
1.115 27 1.10 23
09 June 1999