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The slope and offset for different units when the output is configured for 600 to 1100 mB is given in the
following table:
UNITS
slope
Offset
mB (hPa)
100
600
"Hg
2.953
17.718
kPa
10
60
mmHg
75
450
PSIA
1.4504
8.7023
NOTE: The analog output voltage does take into account the elevation offset (set by the XE or XS
commands). Therefore if the unit's elevation has been entered, it outputs the absolute pressure corrected to
sea level as opposed to the site specific pressure. In other words, the analog output pressure is the same as
the pressure the measure command (M) returns.
Configuring the Operating Mode and Averaging Time
Setting the Operating Mode
The user can select the operating mode of the unit. There parameter that can be either enabled or disabled
is background conversions. Background conversion affects the analog output. If background conversion is
enabled, the ACCUBAR
®
will continually measure the pressure and update its analog output accordingly.
Background conversions add about 7 mA to the quiescent power consumption. With background
conversions disabled, the quiescent power consumption of analog units drops to about 1 mA while for
digital units it drops to about 0.2 mA. Due to the increased power consumption, the background
conversions should not be enabled unless they are needed. If only the analog output is being used and SDI-
12 is not being used, then the background conversion must be enabled. If background conversions are
disabled then the outputs will only be updated if they are enabled and the ACCUBAR
®
performs a pressure
measurement (an M, M1, or M2 command is issued).
If the ACCUBAR
®
is being utilized for both SDI-12 and analog outputs then the user must decide whether
they wish the auxiliary output (analog) to match the SDI-12 readings exactly or whether they should be
updated independently of SDI-12. To be updated independently means that background conversions must
be enabled. To only be updated when SDI-12 readings are performed, the background conversions must be
disabled.
The form of the Command is:
aXOMm!
where a is the address character, XOM is the extended command to set the
operating mode and m represents the operating mode.
The valid values for m are:
0 Background operation disabled for analog units. (Low quiescent power consumption for analog units
being used as a digital only unit.)
16 Continuously update analog output. (Normal operating mode for an analog unit).
Setting the Averaging Time
The ACCUBAR
®
supports user selectable averaging time for SDI-12 readings. The time period in seconds
is specified with the aXT+t extended command.
