Engineering History

ENG History:

• Jan 09: Diamond noise pattern on array in short NDR exposures; horizontal stripes of noise in longer exposures. UIST unavailable for the night; traced to a grounding wire.

• Aug-Oct 08: UIST off scope and warm. New cold-head.

• Jun 08: Throughout the 2 month summer cass block (08A/08B) UIST very occasionally threw up a noisy bottom-right quadrant. Examples images: Full array (GIF), zoom in with slice (GIF) and semi-reduced wce image (FITS) - note that the fits image is flipped horizontally. Occurred once every hundred frames or so; single bad frames were usually preceded and followed by perfectly good frames.

• Nov 07: UIST still off scope though cold. Tests show that the noise in the top two quadrants noticed in July remains. Was initially thought to be bad video boards. However, swapping boards didn't move the noise to other quadrants. Eventually discovered to be "the internal 5vdc interlock cable for the controller that had been tied in very tightly with some of the video board signals, which in turn seemed to have caused the noisy channel on quadrants 1 and 2. After moving the cable away from the rest of the video signals the problem immediately went away."

• Aug-Oct 07: UIST off scope and warm - replacing coldhead and rotating array back to where it was at the start of the year (normal orientation).

• July 07: Noise in the top two quadrants of the array. The problem was in the controller. There is one video board per quadrant so two boards (video 0 and 1) appear to have a bad channel. Video board 3 was swapped out with a spare last December due to a channel problem but hasn't been repaired yet. Can't use WFCAM spares as there are several mods required. See 20070601.009

• May 07: Uist suddenly starts to warmup at 3.30am on 2007-05-26. See this temperature plot of the temps over a five day period (each block is 12 hrs). [Light blue - array, dark blue - coldhead stage 1, red - optical bench]. However, it then starts cooling back down again (with no intervention from us). Pressures were nominal and coldhead sounded fine throughout: suspect a possible clog in the coldhead that cleared itself. Even so, a week later we conducted a mini-warmup to purge the coldhead of the blockage. UIST was down for only one night.

• Apr 07: Array returned and back in UIST. However, bottom-left quadrant found to be dead upon cool-down. Suspect pin alignment. Warmed back up and rotated the array through 180 degs. All four quadrants live following the cool-down, but array is now shifted with respect to the optical path. Result is vignetting in imaging (loss of 4% of the array) and shifted IFU slices (now losing half of one of the slices); all of the reference pixels used with UPICK for imaging acquisition are also shifted, albeit by the same amount in x,y. Living with this for 07A - summer Cass block.

• Mar 07: While UIST warm ship array to Raytheon for QE measurement. Lengthy report delivered.

• Jan 07: UIST warm and open; use LED and detector to measure through-put of optics with Suzie Ramsay Howat. Found to be within ~10% of predicted value for entire optical train. Now question array QE or pupil alignment.

• Jan 07: UIST warm and open: replace L2/L3 lens unit, and install new filter for IJ and JH grisms.

• Oct/Nov 06: David Atkinson visits with SDSU controller (arrives late because of earthquake). Initial problems with not being able to detect light on the array; eventually traced to missing load resistors on the UIST detector board. (With no load resistors all of the outputs were simply being driving to the VddOut output FET drain.) Erik and David fitted 10K load resistors to the video inputs on the four SDSU video boards.

• October 06: Towards end of 06B cassegrain period the UIST temps started to creep up (by a few degrees, though array remained steady at 30K) - fault 20060924.003 and 20061023.002. Traced to vacuum degrading. Pumping from Turbovac on the instrument noticeably improved the temps (reversed the upward trend), and the loss of vacuum was later tracked to the Q3/4 outputs wiring pole connector, which was very loose. Erik tightened the connector down; he also tightened the screws on the other 3 wiring pole connectors which were only slightly loose.

• August 06: UIST back on after summer WFCAM block. UIST removed for possible shipping to ATC (didn't happen); spacers adjusted on new 2pix and 4pix slits for IJ.JH spec (slightly better); new coronagraphic mask installed. OT updated to accommodate posn angles with "imaging" (for coron only), and to make the new slits available.

• January 06: UIST back on after 6 months off for WFCAM. New slits with spacers installed for IJ and JH, plus prototype coronagraphic mask. Slits don't seem to help though, and coron pol mask orientated 90 deg w.r.t. normal pol imaging mask (so dispersion will be along aperture).

• June 05: UIST back on after telescope after WFCAM run. But bad connection to DAQ 2 giving 4-bad/4-good columns in the top-left quadrant. Also, problems with filter wheel 2 stuck, and focus a bit flaky towards end of 2 month run on scope.

• February 05: Grism wheel 2 failure

• Oct-Nov 04: UIST off during WFCAM commissioning. Back on mid-Dec (wasn't opened).

• August 04: UIST warmed up when chiller failed. Back to nominal operating temp after being down for two days (31 Aug/1 Sep).

• August 04: Heavy engineering (rewiring) and computer upgrades in control room, though UIST remained cold and on telescope.

• December 03: UIST off scope (cryogenic/vacuum problems) from Dec '03 until 2 April '04.

• March 03: UIST off scope to replace grisms and filters