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Pressure Systems, Inc. Model 9116 User’s Manual
Page 63 www.PressureSystems.com
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. 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 9116 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 Chapter 4 for additional details concerning the
performance of a Re-zero Calibration.
Note
The calculated offset values from the latest ‘h’ command will be lost
when the module is powered off. To save these offset terms to each
transducer’s non-volatile memory refer to the Set Operating Options
(‘w’) command (index 08).