5
4)
Reassemble the fitting by inserting the tube with preswaged ferrules into the fitting
until the front ferrule seats against the fitting body.
Figure 8 - Ferrules Seated Against Fitting Body
5)
While holding the fitting body steady, rotate the nut with a wrench to the previous
position as indicated by the marks on the tube and the connector. At this point, there
will be a significant increase in resistance.
6)
Tighten the nut slightly.
Figure 9 - Tighten Nut Slightly
2.3 Establishing an Initial Zero Reading
It is imperative that an accurate initial zero reading be obtained for each piezometer as this
reading will be used for all subsequent data reduction.
Generally, the initial zero reading is obtained by reading the instrument prior to installation.
Vibrating Wire Piezometers differ from other types of pressure sensors in that they indicate a
reading when no pressure is exerted on the sensor.
Calibration data is supplied with each gage, a factory zero reading taken at a specific temperature
and absolute barometric pressure is included. (See Figure 18 for a sample calibration sheet.) Zero
readings at the site should coincide with the factory readings within 20 digits after barometric
and temperature corrections are made. (Barometric pressures change with elevation at a rate of
about 3.45 kPa (1/2 psi) per 300 meters (1,000 ft.)
A thermistor is included inside the body of the
piezometer for the measurement of temperature.
