Buck 1011C, Руководство по эксплуатации

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SECTION 4. OPERATING INSTRUCTIONS
4.1 INITIAL SETUP
1. Ascertain that function switch S-1 is in OFF position.
2.
Connect power unit, sensing unit, and control unit to their appropriate cables,
and to 28 VDC (see Figure 13). Also, connect analog or digital recording
devices as desired.
3.
If instrument is to be operated while not in flight refer to section 4.4.
4.2 SYSTEM OPERATION
Turn the function switch to the DEW POINT position and observe the reading settle to its
proper value. The panel meter will read the mirror temperature as it rapidly approaches the
correct dew point. When the unit stabilizes, the D/F point LED will illuminate.
At dew points above 0
°
C, the system stabilizes within a few seconds on the correct dew or
frost layer. Take dew/frost point readings after the D/F point LED has illuminated.
If you connect the RS-232 output to a PC running Hyperterminal, there will be a 1 in the
third position of the line when the mirror temperature and balance have stabilized enough
that dew or frost points are being outputted; otherwise, this will be a zero. Please see page
45 for more details.
4.2.1 Time response
Time response depends on a number of factors: slew rate, dew point, flow rate, and
thickness setting. Slew rate is in turn dependent on dew point and depression; at higher
dew points and moderate depression, it is typically 1
°
C/second. At lower dew points
and/or larger depressions (taken as the temperature difference between the mirror and the
sensor body), slew rate becomes slower, and can be reduced to tens of minutes at its limit.
At low dew points, response is also limited by the reduced availability of water molecules
and the resulting slow crystal growth rate. For best response: (1) maximize flow (to
increase the rate at which water vapor is supplied or carried off); and (2) make sure the
sensor case temperature is kept as close to that of ambient air as possible by proper heat-
sinking and insulation. There is, of course, a trade-off between response time, control
system stability, and sensitivity to contamination.
4.2.2 Mirror cleanliness
It is not necessary that the mirror be “microscopically clean” and, in fact, best performance
will be obtained from a mirror which has been operating for a few hours after cleaning.
On an unscratched, freshly cleaned mirror, there are a relatively small number of
nucleation sites on which dew or frost deposits can form, and so the time it takes to collect
a condensate layer at low frost points is increased. Also, overshoot occurs, which can
cause oscillation.