Pressure Systems 98RK-1 user manual Calibration Adjustment of Offset/Gain Correction Coefficients

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

3.1.5.3Calibration Adjustment of Offset/Gain Correction Coefficients

All NetScanner™ System Intelligent Pressure Scanners have built-in software commands (and pneumatic hardware) to perform a periodic zero and span calibration adjustment of its internal or attached pressure transducers. Use of these periodic adjustments result in the highest possible data accuracy. The result of these calibrations is a new set of internal offset and gain coefficients. These correction coefficients are over and above those factory-determined and unchanging thermal correction coefficients stored in each transducer's non-volatile memory. The factory coefficients provide basic engineering unit conversion capability, while also correcting for various non-linear effects, including temperature effect compensation. The offset and gain correction coefficients provide for fine “linear fit” adjustment of the factory calibration of each transducer. If used properly, the periodic zero and span calibration adjustment should be the only calibration required to maintain specified performance throughout the life of the Intelligent Pressure Scanner.

It is generally necessary for the transducer to have real “zero” and “span” pressure points (specified as 2 or more values) applied when calibration adjustment is required These pressure values may be generated by secondary pressure standards, such as the Model 903x calibrator module or by other external means provided by the customer (such as a dead weight calibrator). For the more common zero-only calibration adjustment, zero differential pressures can typically be provided without the need for external pressure generators. All 9816 models have built-in pneumatic inputs (CAL side inputs) and calibration manifolds required for directing the generated pressures to the various channels of the module(s) being calibrated. Refer to

Chapter 4 of this manual for detailed background and procedures for periodic calibration of the Intelligent Pressure Scanners. A summary of the commands used for calibration purposes is included below.

The Calculate and Set Offsets ('h') command is executed only when a suitable “minimum” (e.g., zero) pressure has been applied to all channels of the module. The new offset coefficients that result from execution of this command are stored in the module’s volatile (or temporary) engineering-unit conversion database. They are also returned to the host in the command’s response.

The Calculate and Set Gains ('Z') command should be executed only when “full-scale” (or other suitable specified up-scale) pressure has been applied to the appropriate channels of a module. The new gain coefficients that result from this command are stored in the module’s volatile (or temporary) engineering-unit conversion database. They are also returned to the host in the command’s response.

In modules using firmware version 2.24 or later, a Configure/Control Multi-Point Calibration ('C') command is provided. This command (actually 4 sub-commands) is an improvement over the single calibration commands ('h' and 'Z') described above. Though 'C' provides for the adjustment of the same offset and gain correction coefficients already described above, it does so with two or more applied pressure calibration points. The final linear fit (i.e., new offset and gain correction coefficients) is a “least squares” correction fit between all the calibration points specified. This 'C' command is particularly useful in calibrating differential transducers over their entire negative-to-positive range.

Although the calculated offset and gain correction coefficients simply remain in volatile memory following execution of the calibration commands (for use by all subsequent EU conversions), they may be optionally stored in non-volatile transducer memory with the Set Operating Options ('w') command (Index 08 and 09).

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