Measurement Specialties 9116 - Manual (Page 34)

Pressure Systems, Inc. Model 9116 User’s Manual
Page 25 www.PressureSystems.com
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 Model 9116 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 need for external pressure generators. All Model 9116 modules 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.