Date: Wed, 15 May 2002 08:45
From: Tomas Chylek
Subject: JCMT_ALL: Central Bearing Adjustment May 14, 2002

  Central bearing adjustment has been successfully performed on Tuesday.
  The weight distribution has been changed so that central bearing now
  carries 85% of the total antena weight. 
  The results are as follows:

  Current antenna mass         : 110 891 kg (corresponds to hydraulic
                                             pressure 7110 psi) 
  Target load on central bearing: 94 258 kg (corresponds to hydraulic
                                             pressure 6044 psi)
  Target load on azimuth rollers: 16 633 kg

  Target adjustment achieved with 2.77% LVDT error

(Click here for full adjustment log details.)

Inclinometry was done thereafter as follows:

    Datasets  El Dirn     HST     mean leg temperatures   Humidity
                          start     start   middle   end       %
  ( 20020429    90 cw     20:54      3.8      3.7    3.3     100 )
    20020514a   90 cw     14:43      4.5      5.0    5.4     100
    20020514b   90 cw     17:57      5.5      5.4    5.1      90     
    20020514c   90 cw     20:51      5.1      4.8    4.4      90
    20020517    90 cw     06:59      0.6      1.4    2.5      75

The temperature data from the fixed TMU inclinometer are OK so data were processed into a track model in the conventional way. The model resulting from the data called 14a is compared with the model from the 29th, and the subsequent data from the 14th are compared with 14a below :

• Justin's 'spikes' are not manifest in the new data, although the temperature range covered is quite small.

• The new track model (as represented in the first plot) is noticeably different from the old, but not in any unexpected way.

• The subsequent data show that the track is stable over the initial hours following a CB load adjustment. While a couple of (electronic ?) spikes affect the second new dataset, the formal differences in (F1,F2,F3) between the last and the first of the new data (plotted above right) are described by the rms scatters of (0.26", 0.08", 0.19"),

• Updates have been made to the plots of symmetry and strain gauge data. The 'symmetry' seemed marginally higher as a result of the CBLA, but settled down through this 3-run sequence, while the strain gauge data show a fairly substantial increase in loads.

• The first of the new models was installed at ~17:30 HST on 14 May 2002.

• 17 May 2002
  A 'cold' data set were taken and are compared below with the 'warm' dataset '14a' :
  

  The data show that the track profiles change with a ~5deg change in temperature by about 1-2", but there is no obvious sign of the 'spikes'. The updated symmetry and strain gauge data look OK, even if the wheel loads are reduced from the measures immediately following the CB load adjustment

  Which track profile should be installed ? 'cold' or 'warm' ?