Geometrics Memory-Mag G-856AX, Руководство по эксплуатации

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Geometrics, Inc
.
G-856AX Operation Manual
47
will need a small pointed object like a pencil tip to change the switch settings. Notice
that the switch position are labeled 1 through 8 and that the ON position is identified by a
dot or labeled ‘ON’ depending on the switch model. Typically, switches 1 through 5 are
off and switches 6 through 8 are on. The functions of these switches and the operation
state associated with their settings are summarized in Table 4.
Table 4. Summary of programmable switch settings.
Switches Function Settings State
S1 OFF S2 OFF Normal
S1 ON S2 OFF Long
S1 ON S2 ON Short
1, 2 Polarize time
S1 ON S2 ON Short
S3 OFF Normal –920 ms 3 Read time
S3 ON Short – 460 ms
S4 OFF Normal 4 3 Reading average
S4 ON Average
S5 OFF Normal 5 Auto cycle display
S5 ON Display shuts off
S6 OFF S7 OFF S8 OFF 110 baud
S6 ON S7 OFF S8 OFF 150 baud
S6 OFF S7 ON S8 OFF 300 baud
S6 ON S7 ON S8 OFF 600 baud
S6 OFF S7 OFF S8 ON 1200 baud
S6 ON S7 OFF S8 ON 2400 baud
S6 OFF S7 ON S8 ON 4800 baud
6, 7, 8 Baud rate selection
S6 ON S7 ON S8 ON 9600 baud
Polarize and count time – Switches 1 through 4
There are two stages in the process of obtaining a magnetic field measurement using a
proton-precession sensor. During the first stage (polarize cycle), a current is fed to the
sensor coil. This coil is immersed in sensor fluid and the current flow generates a
magnetic field in this fluid that causes the spin axes of the hydrogen atom’s protons to
align. When the polarizing current is removed the protons precess about the ambient
magnetic field and this precession frequency is counted for a short period of time (count
cycle). There are tradeoffs in the amount of time provided for the execution of each of
these cycles.
The polarizing current should be left on long enough to completely align the proton’s
spin axes (to produce a good signal precession signal), but not so long that battery power
is wasted or the measurement time becomes inconveniently long. The count cycle should
be relatively brief: the amplitude of the precession signal decays rapidly and it is best to
obtain readings by counting its frequency early when the signal is strongest. Selection of
the best counting period will depend on the polarization current, the ambient magnetic
field strength, and the ambient magnetic gradient. High polarization current and/or high
ambient magnetic field strength will produce more precession signal but high magnetic
field gradient will cause the signal to collapse more rapidly.