Inclinometry data from 24 & 25 February suggested a precipitous drop in wheel loadings and an unplanned central bearing adjustment was scheduled for 05 March. Despite the lack of confirmation of this scenario in subsequent inclinometry the central bearing load adjustment progressed as scheduled :

   Date: Wed, 06 Mar 2002 09:29:13 -1000
   From: Tomas Chylek 
   To: "JCMT (All) List" 
   Subject: JCMT_ALL: Central Bearing Adjustment March 05, 2002

   Unscheduled central bearing adjustment has been successfully 
   performed . . . it did not confirm observed decreased load on the
   rollers. The setup achieved after previous bearing adjustment
   (December 2001) was found undisturbed. The results are as follows:

   Current antenna mass           : 111 250 kg 
      (corresponds to hydraulic pressure 7133 psi) 
   Target load on central bearing : 99 600 kg 
      (corresponds to hydraulic pressure 6384 psi)
   Target load on azimuth rollers : 11 680 kg

   Target adjustment achieved with 1.43% LVDT error

Full adjustment log details can be seen here

Inclinometry
The CB work was followed by inclinometry using the fixed inclinometer on the TMU and with the antenna near the zenith. Unfortunately, these data were again corrupted, in a manner similar to those of 03 March (above), and 17 Oct 2001, with both the TY (tilt, Ch2) and TT (temperature, Ch3) data streams corrupt.

[ For demonstration purposes, they were processed (without temperature correction) to the 'model' stage and compared with the previous el=90 model - see this plot].

The time was then ~18:30 HST, and the 1^st shift observers (Thomas & Remo) were expecting to perform all-sky pointing. It was necessary, instead, to repeat the inclinometry. The corrupt data suggests (as it did previously), that either the 'fixed' TMU inclinometer is faulty or suffers from being plugged into/unplugged from the A-D units, or the A-D units have some intermittent fault. The good behaviour of the signal from the X-axis supports an internal fault. In any case a second inclinometry run was made with the 'tiltable' inclinometer and with the antenna at elevation = 60^o. However, to add to the complications, the TMU zero-points have changed recently, so the instructions for setting the TMU position in order to place the inclinometer near the horizontal were no longer valid. Thomas & Remo spent the best part of an hour finding new values. (My thanks).

    Datasets El Dirn     HST     mean leg temperatures   Humidity
                        start      start   middle   end       %
  ( 20020213 90 cw       00:00     -0.2      0.0    0.1      80 
    20020218 60 cw       20:59      3.7      3.7    3.6     100 
    20020303 90 cw       10:42     -1.8      0.0    1.5      25
    20020305 90 cw       15:43       -        -      -        - )
    20020305 60 cw       21:00      1.6      1.2    0.9      80

The model resulting from these el=60 data are compared below with the previous ('spike'-free) model of 13 Feb, and with the el=60 model of 18 Feb :

The new data look fine, clean, and free from 'spikes', as was the case on 03 Mar. Again - updates to the plots of symmetry and strain gauge data show no confirmation of the low wheel loading seen in February.

The new model was installed at ~03:00 HST 06 Mar 2002.

A dedicated allsky pointing run has been requested in order to update the pointing model, but initial data from the evening of 06 March (HST) shows reasonable performance using the old model still.