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Pressure Systems, Inc. 98RK-1 & 9816 User’s Manual©
Page 102 www.PressureSystems.com
4.2 Re-zero Calibration
NetScanner
™
System 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 with 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 the Model 9816, with its integral DH200 pneumatic transducers, internal manifolds and
valves allow a Re-zero calibration to be accomplished easily and automatically.
Before executing the Re-zero calibration adjustment function, a stable 0.0 psi differential
pressure should be applied to the appropriate CAL (x) and CAL REF input port of the 98RK-1.
Unless the optionally-specified pressure parameter of the Calculate and Set Offsets (‘h’)
command (described fully in Chapter 3) is used, the 9816 will assume 0.0 psi is applied to the
affected channels.
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.
Note
When using the Calculate and Set Offsets ('h') command, 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 4.5 if it is
desired to also store these new offset coefficients in transducer
nonvolatile memory.
4.2.1. Re-zero Calibration Valve Control
When instructed to execute a Re-zero (Calculate and Set Offsets ('h') command), Model 9816
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 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.