4-2
Calibration of all transducers is to be performed "in the system, as a system". There are no
provisions for, nor is it recommended that calibration of any of the transducers (temperature,
pressure, or flow) be performed while electrically disconnected from the generator. Since all
calibration is performed mathematically by the computer, there are no manual adjustments to
make.
Calibration is performed on all of the transducers by solving for the coefficients A, B, and C
of the quadratic formula:
Y=A+Bx+Cx
2
where x is the raw count (or uncalibrated output of the A/D
converter) while measuring a transducer, and
Y is the desired value (the standard or reference
transducer's reading) for the transducer being calibrated.
The three coefficients A, B, and C are found by applying three separate, distinct, and stable
references to each transducer, measuring the resulting raw count, then solving the
mathematical system of three equations with three unknowns. Since all of these calculations
are performed automatically by the 3900's embedded computer, the operator need only be
concerned with providing three known stable references required for the calibration of each
transducer.
4.2.1 A/D Card
Equipment Required: (None)
All calibration errors appearing in the A/D card will be accounted for automatically during
calibration of the temperature, pressure, and flow transducers. The card is also equipped with
built in auto-zero and auto-span circuitry which automatically and continually accounts for
short and long term drift in measurement accuracy. No user calibration is required. A card
suspected of extreme inaccuracies or malfunctions should be sent to the factory for repair.
4.2.2 Temperature Calibration
The systems EDIT/CAL mode may be used in conjunction with a precision temperature bath
for temperature probe calibrations. Only one temperature probe may be calibrated at a time.
By using the temperature bath to generate three known temperatures, all coefficients (ZERO,
SPAN, LINEARITY) can be calculated automatically by the embedded computer and used to
update the system calibration. A new expanded calibration report may also be printed at the
conclusion of the calibration sequence.
