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Pressure Systems, Inc. NetScanner™ System (9016, 9021, & 9022) User’s Manual
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3 - 49
CALCULATE AND SET OFFSETS (Command ‘h’)
Purpose: Instructs a module to calculate new offset coefficients with zero differential pressure
(or a specified “generated” pressure) applied to the specified channels. These new
coefficients update part of the module’s internal calibration coefficient database,
used to convert any subsequent raw data into engineering units data. The new
offset values are also returned in the response. This command is sometimes called
a Re-zero or zero-only calibration.
Command “hpppp [vv.vvvv]”
‘h’ is the command letter
‘pppp’ is the position field
‘vv.vvvv’ is an [optional] applied pressure value preceded by a space
character
Response “g.gggg .. [g.gggg]...”
‘g.gggg’ are the actual offset data values returned, each preceded by a space.
Description: The position field may have 0 or 4 characters. If no position field is specified,
offset coefficients for all of a module’s input channels will be calculated and
returned. If a position field is specified, offset coefficients for only the channels
whose bits are set (=1) will be calculated and returned. If the optional pressure value
[ vv.vvvv] is specified, the position field must be 4 characters, even when all
channels are to be specified. If the optional pressure value [‘vv.vvv’] is not
provided, an applied pressure of 0.0 psi(a) will be assumed when calculating
coefficients. When using the 9021/9022 module with 9401 absolute pressure
transducers, it will usually be required to use the applied pressure field [‘vv.vvv’] as
it may not be possible to apply 0.0 psia to the 9401 transducers. Offset values are
returned in the response in order of highest specified channel to lowest specified
channel, with data formatted per an implied decimal format (f=0).
Before acquiring data with this command, any addressed Model 9016 module will
normally attempt to place the calibration valve in the CAL position, so that a zero
differential pressure can be applied to all channels via the module’s CAL and CAL
Ref input port. Simply leaving these ports unattached will allow the transducers to
read the appropriate zero differential pressure if ambient air pressure is stable. After
data are acquired, the calibration valve will be placed in the RUN position. To
disable the automatic shifting of the calibration valve, refer to the Set Operating
Options (‘w’) command (index 0B). The reader is also referred to Section 4.2 of