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Addendum
748461-B
April 2003
http://www.processanalytic.com
Model NGA2000 PMD, NDIR
VAISALA BAROMETRIC PRESSURE TRANSDUCER
This addendum serves as an amendment to
the Model NGA 2000 PMD and NDIR instruc-
tion manuals. The following information
should be considered part of the manual, if
your instrument has a Vaisala Barometric
Pressure Transducer installed in it, or if you
are retrofitting a PMD or NDIR with a Vaisala
transducer kit.
The Vaisala PTB100 series Analog Barometer
is a N.I.S.T. traceable precision silicon capaci-
tive atmospheric pressure transducer. The
sensor delivers an analog voltage output that
is inversely proportional to its inlet pressure. It
has an operational ambient pressure range of
800 to 1060 hPa.
The original PMD and NDIR instruments were
designed for use with a resistance bridge type
of pressure transducer requiring an external
gain amplifier with an offset trim The Vaisala
transducer contains an integral gain amplifier
that is scaled for a 0 to +5 Vdc output. The
661380 “Interface Board” contains the cir-
cuitry to convert the Vaisala single ended 0 to
+5 V dc output into the referenced bridge 0 to
+0.625 V dc output configuration that is re-
quired by the Analyzer module’s Computer
Analysis Board. The Vaisala transducer kit is
backward compatible with the original Rose-
mount pressure transducer.
Vaisala Interface Board Circuit Function:
The Vaisala Interface Circuit board adapts the
single ended analog output of the Vaisala
sensor into a Precision Voltage referenced,
balanced bridge (at 1 atmosphere) input con-
figuration. A “Bridge Balance” pot on the
Vaisala Interface Circuit board provides the
fine trim “Bridge Balancing” calibration ad-
justment that is required to set up each indi-
vidual transducer at a known ambient air
pressure. Test points are provided on the cir-
cuit board for this adjustment.
The Vaisala transducer output range is 0 to
+5 Vdc.
The Vaisala analog output voltage is inverted
and fed into a balanced summing node that is
referenced by a precision regulator. The
summing node voltage is 0.000 Vdc at 1013
hPa (1 atmosphere ambient air pressure). The
summing node voltage is then buffered, in-
verted, and gain reduced by a factor of 8 to
produce the Pressure Compensation Output
voltage at J12-1 for the Computer Analysis
board.
Low noise, Low input current offset Op-Amps,
and common substrate resistors are used to
reduce gain tracking errors and null thermal
coefficient effects.
1-1 INSTALLATION & RETROFIT
INSTRUCTIONS
1. Remove the original Rosemount trans-
ducer circuit board assembly, located on
the motherboard at J12 and J13 (if pre-
sent).
2. Install the transducer with the pressure
inlet facing the rear of the instrument us-
ing the mounting studs provided on left-
hand side of the detector housing.
3. Install the Interface board into it’s mating
sockets (J12 and J13) on the mother-
board.
4. Connect the 4-pin cable (P1) from the in-
terface board (noting pin polarity) to the
Vaisala Pressure Transducer.