Pressure Systems, Inc. Model 9116 User’s Manual
Page 93
www.PressureSystems.com
4.2 Re-zero Calibration
All
Model 9116
Intelligent Pressure Scanners are capable of independently performing a
transducer calibration adjustment function, referred to as
Re-zero adjustment
(or simply Re-zero
Cal). The Re-zero calibration will result in a recalculated “offset” coefficient for each channel
being calibrated, which automatically compensates for any transducer offset drift errors. Since
the factory-set coefficients in each transducer (that characterize both pressure and temperature)
are extremely stable over time, these simple offset corrections compensate for the majority of
transducer errors over time. For this reason, a Re-zero may be the only calibration adjustment
required by many applications. For those applications requiring more accuracy, an optional
single-point Span-only calibration adjustment will be described in
Section 4.3
. An improved
multi-point calibration adjustment, integrating both the Re-zero and Span calibration process will
be described in
Section 4.4
.
For
Model 9116
, with integral DH200 pneumatic transducers, internal manifolds and valves
allow a Re-zero calibration to be accomplished easily and automatically.
When instructed to execute a
Calculate and Set Offsets
(
‘h’
) command, the
NetScanner
™
System
module will automatically perform the
Re-zero adjustment
calibration, and then update
the
offset coefficients
in its volatile memory. It will subsequently use the newly calculated terms
for all future engineering-unit calculations until power is lost to the module.
Note
When using the
Calculate and Set Offsets
command (‘h’), only local
terms in the module’s volatile main memory (RAM) are updated.
Under normal operation, it is not recommended to store these new
coefficients in transducer non-volatile memory. Instead, the re-zero
should be performed at regular intervals..
4.2.1. Re-zero Calibration Valve Control
When instructed to execute a Re-zero (
Calculate and Set Offsets
(
‘h’
)) command,
Model 9116
modules will normally shift the internal calibration valve into the
CAL
position and use the
pressures present at the
CAL
and
CAL REF
inputs for the “minimum” (e.g., zero) calibration
pressure. After the Re-zero adjustment is complete, the
Model 9116
calibration valve will be
placed in the
RUN
position. This automatic shift of the calibration valve can be disabled through
use of the
Set Operating Options
(
‘w’
) (option index=0B hex) command. This allows
independent control of the calibration valve by the user using other options (see
option indexes
= 0C and 12 hex) of the same command.
