Geokon 4580, Instruction Manual

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2
2. INSTALLATION
2.1 Preliminary Tests
Upon receipt of the pressure transducer the zero reading should be checked and noted (see
Sections 3 for readout instructions). A thermistor is included inside the body of the sensor (as
shown in Figure 1) for the measurement of temperature (see Section 3.4 for measurement
instructions).
Calibration data are supplied with each gauge and a zero reading at a specific temperature and
barometric pressure. Zero readings at the site should coincide with the factory readings within 20
digits after barometric and temperature corrections are made. The factory elevation is +580 ft.
Before March 21, 1995, factory barometric pressure readings were corrected to sea level;
readings after this date represent absolute pressure. (Barometric pressure changes with elevation
at a rate of ≈ ½ psi per 1,000 ft.) See Appendix D for a sample calibration report. Note that the
calibrations were performed with the sensor vertical, cable end up.
The sensor is very sensitive, and it will be observed that the readings change depending on the
position of the sensor. A 30 to 50 digit change between the sensor being vertically up and
vertically down is normal. This phenomenon will not be a problem if the sensor remains
stationary or is in the same orientation during use. Additionally, these sensors are sensitive to
shock, particularly the very low-pressure versions. A shift in the zero reading can occur during
shipping or rough handling. Normally this will not affect the operation of the sensor, but a shift
of more than 100 units should be checked out by monitoring the sensor for a few days at a
constant temperature, if possible.
2.2 Model 4580 Installation
2.2.1 Barometer
The barometric sensors are calibrated at the factory and referenced to an absolute
barometric reading in millibars. Installation at the site is usually carried out by installing
the sensor in a vented enclosure with the sensor in a vertical position with the cable
exiting from the top of the sensor. (The sensor is position sensitive and is calibrated in the
vertical position.)
Transducers of this type have very high sensitivities and are usually somewhat susceptible
to shocks of the type that can occur during shipping. It is therefore advisable to obtain
concurrent readings with an accurate, local barometer following installation to be sure of
obtaining a proper onsite starting point for all measurements.