Pressure Systems 9022 Instrukcja Użytkownika Pobierz pdf (Strona 116)

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Measurement Specialties Inc. NetScanner System (9016, 9021, & 9022) User’s Manual

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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 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.

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.

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Pressure Systems 9022 Instrukcja Użytkownika Strona 116