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AZ: Zero the Azimuth Tracker
The AZ command orients the Azimuth Tracker to its zero-step position. This routine is activated
automatically following a system reset (RE command). The operator should use this command if
there is concern that the azimuth drive has lost track of where it is for such reasons as temporary
power loss to the Tracker or other physical disturbance.
Note that the AZ routine can only be accessed if the instrument configuration (IC) is setup to include
an Azimuth Tracker System.
Method:
Type AZ . The following screen display appears while the program steps the azimuth drive towards
its internal optical reference sensor:
*** zeroing azimuth
press Del to abort
The operator can abort the operation by pressing the DEL (delete) key; the program will return to
the previously displayed menu. When the program has located the reference flange it compares
the predicted and actual sensor positions, then displays the step discrepancy on the screen for
about 5 seconds:
*** discrepancy = n
AZIMUTH ZEROED AT HH:MM:SS DISCREPANCY = N
N will usually be a small integer lying in the range -10 < N < 10. (The Tracker stepper-motor
gearing is approximately 15000 steps per revolution, so a discrepancy of 10 steps corresponds to a
positional error of 0.2° ). N will be much larger if the Brewer has recently been reset or if the Tracker
has been physically perturbed (eg power interruption).
The Azimuth Tracker then returns to the solar azimuth and the previously active menu is displayed.
DT: Photomultiplier Deadtime Test
The DT test measures the deadtime of the photomultiplier and photon-counting circuitry. This test
takes readings at four slitmask positions:
Slitmask Position
1
3
5
7
Position 7 allows simultaneous observation through slits 2 and 4. Dark count-corrected counts are
stored in the BASIC F() array (refer to the Preliminary Data Reduction document for details). The
following algorithm is used to derive a value for instrument deadtime:
Assume Poisson statistics:
τ
−
N
⋅
=
⋅
N
N
e
0
0
N
1
τ
=
⋅
log
e
N
N
0
where:
N
is the true count-rate (counts/sec),
o
N is the observed count-rate,
τ is the deadtime (sec). (The BASIC variable T1 is used for τ .)
94
Description
Darkcount
Wavelength 2
Wavelength 4
Wavelength 2&4
0
MKIV OPERATOR'S MANUAL
BASIC Variable
F(1)
F(3)
F(5)
F(7)
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