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Long-term monitoring of the inclinometry system was performed by running the
INCLINE software while the telescope was unused for several hours. The data were
analysed channel by channel to derive zero-point drifts with time or
temperature.
Datafile Start Date/Time Sample Time Length
STATIC4 Sep 28 22:25 10 secs 9.4 hrs
STATIC5 Oct 16 10:06 10 secs 7.4
The temperatures measured by the inclinometers on the right and left A-frames
(RT, LT, respectively, in mV) were compared with
temperatures RAT, LAT, (in deg C) from the antenna leg temperature system
(specifically the mean of the probes 2 & 8 and 1 & 7 on the lower parts of the
A-frames) to yield the following relations :
RAT = RT * 0.226 - 15.6 from the 940928 data
LAT = LT * 0.223 - 13.6
RAT = RT * 0.244 - 17.3 from the 941016 data
LAT = LT * 0.211 - 11.9
The temperature range covered by these data is 1degree - 5degree on both
occasions. The accuracy of the individual relationships are about 0.1degreeC.
The data for the right A-frame are fairly similar and together yield
RAT = RT * 0.226 - 15.6
but the left A-frame data are at least 0.5degree different in zero-point,
although their slopes are similar. Further data are needed in order to better
understand how these temperature channels may be used or to establish if this
effect is due to hysteresis. The accuracy of the temperature probes within the
inclinometry units is apparently only 1degreeC, which might ultimately make them
fairly useless in this regard.
Similar data for the TMU (TT), comparing with the upper legs (probes 3, 4, 5 &
6) is not yet available.
The inclinometer measures show variations with the temperature measured
from that inclinometer unit as follows :
s.e.(mV) range of T
LX = -0.698 * LT**2 + 90.1 * LT - 2427 3.7 70 -> 82
LY = -0.264 * LT**2 + 39.5 * LT - 1469 2.8 67 -> 82
RX = 0.816 * RT**2 - 120.1 * RT + 4213 3.6 74 -> 90
RY = -0.146 * RT**2 + 21.8 * RT - 1223 1.3 74 -> 90
These variations are due to a combination of the variations
(with time/temperature) of the zero-points of the inclinometers, and of the
actual tilt of the beams they're on. The accuracies correspond to about
0.05".
It may be possible to eliminate the tilting of the beam (or of whatever surface
they're on) by mounting two inclinometers in close proximity. Both would then be
affected by the same tilt. However, the difference of the output would show the
variation of the difference in their zero-points, but not of either
zero-point seperately. Their extension to warmer and colder operating
temperatures requires further data. Future work on zero-point drifts may be
the subject of a later, separate, report.
Next: Calibration
Up: Measurements - September
Previous: Measurements - September
Iain Coulson
Thu Mar 13 13:57:23 HST 1997