Pressure Systems 9022 Manuel d'utilisateur télécharger pdf (Page 42)

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

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3.1.4.2 Module Data Acquisition

After power-up, all modules will begin to scan all attached transducer channels in channel

number order. Scanning will occur at the module’s maximum internal rate (using the previously

stored number of data averages per channel). The data are stored in an internal buffer, available

for retrieval by the host computer. Engineering units conversion of the scanned channels is

accomplished using thermal correction data extracted from each transducer at power-up. While

scanning, the module will automatically monitor the attached transducer’s temperature,

correcting engineering unit output for any temperature effects.

All modules effectively defer the host computer’s decision of “which channels of data do I want”

until that time when the host chooses to send read commands to actually retrieve the desired data

from the latest “buffered copy” of the continuously scanned, averaged, and

engineering-unit-converted data.

See Section 3.1.4.4 (Delivery of Acquired Data to Host) for more information.

While scanning, all modules take multiple samples and average each channel. The number of

samples per scanned channel defaults to 8, but may be set to one (to disable averaging) or to any

power of 2 (1, 2, 4, 8, 16, 32) to change the degree of averaging (and its effect on maximum scan

rate). The Set Operating Options (‘w’) command may change this variable at any time.

3.1.4.3 Calibration 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 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 the 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 through the life of the

Intelligent Pressure Scanner.

It is generally necessary for the transducer to have real zero and span pressure (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 9016 models have built-in pneumatic

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Pressure Systems 9022 Manuel d'utilisateur Page 42