Pressure Systems 9816, 98RK user manual Re-zero Calibration Valve Control

Pressure Systems, Inc. 98RK-1 & 9816 User’s Manual©

4.2Re-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-pointSpan-onlycalibration 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.

When using the Calculate and Set Offsets ('h') command, only local Note 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.

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