Pressure Systems 9022 - Manual (Page 39)

Pressure Systems, Inc. NetScanner™ System (9016, 9021, & 9022) User’s Manual
www.PressureSystems.com 3 - 9
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 are 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