Pressure Systems 9022 - Manual (Page 114)

Pressure Systems, Inc. NetScanner™ System (9016, 9021, & 9022) User’s Manual
www.PressureSystems.com 4 - 4
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. Refer to Section 4.6 if it
is desired to also store these new re-zero terms in transducer nonvolatile memory.
4.2 Re-zero Calibration
The NetScanner ™ System Intelligent Pressure Scanners including Models 9016, 9021, and 9022
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 9016, with integral DH200 pneumatic transducers, internal manifolds and valves allow
a Re-zero calibration to be accomplished easily and automatically. For Models 9021 and 9022,
which have external 9400, 9401 or 9402 (or third-party) all-media transducers, the user must supply
any necessary valves and controls to accomplish the application of a “minimum” pneumatic or
hydraulic pressure to these transducers before executing the re-zero adjustment.
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.
4.2.1. Re-zero Calibration Valve Control
When instructed to execute a Re-zero (Calculate and Set Offsets (‘h’)) command, Model 9016
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 9016 calibration valve will be placed
in the RUN position. Models 9021 and 9022 assume a “minimum” calibration is already applied
to the transducers. This automatic shift of the calibration valve can be disabled through use of the