Radial-arm Inclinometry before (951026) and after (970712) the track welding

1. The data of 951026 were taken with the inclinometer on the radial arm between the central bearing and the back left wheel, whereas almost all the data since then has been taken on the back right wheel : this followed the identification in early 1996 of a problem with the back right antenna wheel that ultimately led to its replacement.
2. The orientation of the inclinometers was changed at this time also. The older configuration had the Y-axis pointing radially outwards and the X-axis pointing CW, whereas the current configuration has the X-axis pointing radially outwards and the Y-axis pointing CCW.
3. The earlier data (951026) were taken after the first track weld was made of joint 4/5.
4. The installation of SCUBA in mid-1996 has undoubtedly changed the loading on the wheels.

1. A possible scaling error remains, but should not affect a qualitative comparison of the joints as felt by the different wheels, The use of different wheels requires that the data be adjusted in phase before the comparison : the angle between the back legs is 96.8 degrees. Otherwise, the data have been processed identically; a remove-linear-baselines adjustment based on data from the intervals (30,50) and (390,410), and identical scaling (20"/mV).
2. Possible scale and behavioural differences exist between the X- and Y- axes, but manufacturer specifications and empirical data suggest that these are negligible.
3. This effect also is negligible and actually provides a qualitative reference.
4. Loading changes might mimic scale changes.

   The comparison of the entire radial arm datasets is shown . Aside from a reduction in the overall tilt of the track or building - which is the largest effect in this diagram - there is a general increase in the amplitudes of the bows in the 970712 data. This was somewhat surprising and worrying.

   However, closer examination of the data, on a joint-by-joint basis, reveals general removal of sharp steps and transfers, and general rounding of steep parts of the track profile. These are more important gains to the track upgrades program than the moderate and tolerable increases in bow amplitudes which are easily accomodated by the inclinometry. A qualitative comparison of the joints before and after appears in the following table. (Note that the azimuth in column two is that of the interaction between the joint and the back-right wheel, and that the diagrams, except that for the joint 1/2, show the azimuths of all nearby joint-wheel interactions.)

   Joint	Azimuth	New cf. Old
   1-2	169 (*)	step removed
   2-3	196	step considerably softened
   3-4	217	step removed
   4-5	244	unchanged (welded prior to 951026)
   5-6	271	step removed and generally softened
   6-7	292	larger bow amplitude, but slightly gentler step
   7-8	319	larger bow amplitude, gentler step
   8-9	346	larger bow amplitude, gentler step
   9-10	13	bow amplitude doubled
   10-11	40	joint kink removed
   11-12	67	severe steepness removed
   12-13	94	5" step reduced to 1"
   13-14	115	sharp step softened
   14-1	142	15" step softened and reduced to 5"
   Joint	Azimuth	New cf. Old
   (*)		displayed for clarity without azimuths of joints shown

   In almost all cases the welding has been beneficial.

   Ian Pain has static measures of the joint improvements that will appear in a document summarizing the track improvements project. The improvement of the track should really be tested by repeating the inclinometry-tracking-inclinometry tests we did a year or two ago, and a plan of action to request appropriate telescope time will be drafted soon.

   For a better comparison, we should also try to get new radial arm inclinometry with the old configuration.

   970804 : Note : such data were obtained on 970801 and are now included in the above figures.

   Return to POINTING REPORTS

   imc 970731