7.
Calibration
The ACCUBUBBLEs under go a rigorous screening and testing at the factory before they are shipped to
ensure that they meet their accuracy specifications over temperature and that they are stable both in zero and
span and will continue to be accurate over time. Any drift in the zero of the unit can be easily checked by
opening the input to atmosphere and performing a measurement. Any drift can be nulled out via the XS
command. Span drift is much more difficult to determine. The span drift of the ACCUBUBBLE in the field
is typically less than 0.01% per six months. This is a small fraction of the stated accuracy of the
ACCUBUBBLE. The stated accuracy of the 5600-0131 ACCUBUBBLE at its full scale reading is 0.1% of
reading, although typically it is much better. Even though it would typically take over 5 years for the
ACCUBUBBLE to drift as much as 0.1%, it is recommended that the ACCUBUBBLE, like all precision
measurement instruments, be placed on a periodic calibration schedule.
Factory Calibration
The initial factory calibration of the pressure sensor typically includes over 1000 different pressure
temperature points that cover the complete temperature range from -40 to +60 degrees C and cover the
complete pressure range from 0 to 22 PSI for the 5600-0131 and 0 to 50 psi for the 56-0131-50. This
ensures that the ACCUBUBBLE meets the specifications over the complete pressure and temperature range.
A calibration verification encompasses nearly 200 points over the complete temperature and pressure range.
ACCUBUBBLEs can be sent back to the factory for a complete calibration over temperature. The Sutron
Part number for this calibration service is: 8700-0005
Metrology Lab Calibration
The ACCUBUBBLE does have the provision for a calibration to be performed by a Metrology Lab. The
calibration coefficients that can be entered by a metrology lab are a scale and an offset parameter. There is
not a provision for any temperature dependent parameters. Most metrology labs would not have the
capabilities to provide a calibration over temperature and pressure. To accurately calibrate an
ACCUBUBBLE requires a reference accuracy on the order of 0.001 PSI (8 Pa).
To collect data for calibration of the ACCUBUBBLE, the M1 command should be utilize. This will ensure
that field offset or old calibration coefficients do not affect the accuracy of the data collected. The command
that is utilized to enter the Metrology Lab Coefficients is:
aXCosc!
Where a is the address character, XC is the extended command to set the
calibration coefficients, o is the offset in PSI, s is the scale factor, and c is the
checksum.
The Checksum is the 8 bit sum of the 7 bit ASCII characters (parity is striped) from and including the
address character through the last character of the scale factor. It does not include the checksum string or its
delimiting polarity sign. The checksum is transmitted as an ASCII string. That means that if the 8-bit sum is
236 then the value of c is +236. The command to set the offset of the unit at address 0 to 0.0000 and the
scale factor to 1.0000 would be:
0XC+0+1+130!
The calibration coefficients affect the output of the M command, the analog output, and the quadrature
output. This command does not affect the output of the M1 command. The data output by the M command
is computed from the following equation:
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Sutron Corporation, 21300 Ridgetop Circle, Sterling, Virginia 20166-6520
45
Содержание Accububble 56-0131-50-1
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