F:\MARKETING\TECHNICAL MANUALS\Air Samplers\DF Battery TECH MANUALS\DF-75 LPM SERIES.doc
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SENSORS
FLOW SENSOR:
The Digital Flowmeter Battery Series Air Samplers com equipped with a precision-machined
differential pressure sensor. The relationship of the differential pressure across the sensor as a function
of flowrate is stored in the microprocessor and utilized as the starting value to determine the flowrate
and totalized volume corrected to a reference temperature and pressure. The purchaser selects the
conditions at the time of purchase. Four choices are available.
TEMPERATURE SENSOR:
A thermistor temperature sensor is placed in-line in the air stream at the entrance to the venturi to
accurately measure the temperature of the air that is flowing through the flow sensor. The accuracy of
the temperature sensor is +/- 0.9ºF (0.5ºC).
DIFFERENTIAL PRESSURE SENSOR:
A precision electronic differential pressure sensor measures the differential pressure across the flow
sensor. The total system accuracy of the digital flowmeter air sampler flow sensor and the differential
sensor electronics is accurate to ± 4%.
The electronic differential pressure sensor offset value is automatically calibrated once per minute to
eliminate sensor drift problems. Once per minute the electronic value correlating to a differential
pressure of 0.00 inches of water is measured and stored in the on board computer. This ensures that all
flow rate determinations for flow rate are unaffected by sensor electronic drift. This is especially
important for low differential pressure measurements.
PRESSURE SENSOR:
A precision pressure sensor accurately measures the absolute pressure at the inlet of the flow sensor to
± 1% over the measured range.
The sensors are calibrated across the range of approximately 22 inches to 29.92 inches of mercury.
This corresponds to an approximate range of 7000 feet elevation down to sea level. The reference
value for pressure correction has been chosen to be 1 atmosphere of pressure (29.92” Hg). A custom
reference for unique customer requirements is available as an option for a fee.
