Setra System Model 470 - Manual (Page 19)

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2. The transducer reports a sequence of information which indicates the status of any
functions which are currently in use and some blank lines, as shown in this example:
STATUS:
Elev:
256 FT.
Max: 14.4193 PSI A
Min: 14.5188 PSI A
HI A: 15.8000 PSI A
LO A: 11.0000 PSI A
Zero: 1.0000 PSI A
Stab: 0.0005 PSI A
Unit: 1 PER PSI
In the example above:
“Elev” shows the DASI station elevation (Section 4.11).
“Max” and “Min” show the maximum and minimum pressures applied to the sensor (Section
4.5), if the min/max function is active.
“HI A” and “LO A” show the high and low alarm setpoints (Sections 4.6, 4.7).
“Zero” shows tare value (Section 4.8) currently in memory, if it is non-zero.
“Stab” shows the user defined stability indicator limit (Section 5.8).
“Unit” shows the user definable conversion ratio (Sections 4.3, 4.4), if it is in use.
4.11 Digital Altimeter Setting Indicator (DASI)
The Setra 470 DASI (Digital Altimeter Setting Indicator) function reports corrected sea level
pressure by “reducing” true barometric pressure at a known elevation to the pressure which
would be measured at sea level at the same location.
To perform the correction of true pressure to sea level pressure in the following procedure, you
must know the Station Elevation (the altitude above sea level) at which the transducer is installed.
The terms “Station Elevation” and “Reduction of Pressure” have very specific meanings in the
jargon of Altimeter Setting Indicators. These terms and the actual calculations performed by the
Setra 470 are detailed in “Smithsonian Meteorological Tables, Vol. 114”. For more information,
contact Setra.
On power-up, the Station Elevation (which is set by the SETUP SEA LEVEL command) is set to
0. Any Station Elevation entered by the user before power-down is not retained on power-up.
To use the DASI function, follow this procedure:
1. Use the CONVERT function (see Section 4.2) so that the 470 reports data in units of
pressure in response to an interrogation. (i.e., the transducer should not be reporting in units
of altitude.)
2. Transmit SB, for SETUP SEA LEVEL.
3. Transmit the station elevation (the altitude above sea level at which the transducer is
installed) in feet or meters.