RST Instruments VW2100, Инструкция по эксплуатации, Страница: 10 / 34

VW2100 Vibrating Wire Piezometer
Instruction Manual
ELM0005P RST Instruments Ltd. Page 10
initial readings at the “zero point” is extremely important for the accuracy of the
subsequent readings.
Before installing the vibrating wire piezometer, it is necessary to take the initial zero
reading with no applied load. The initial zero reading can be taken in one of the
following ways:
•
With the filter stone removed, or
•
With the stone completely saturated and installed.
More information can be found in Section 5.1 and Appendix B.
If the filter stone is saturated, initial zero readings should be taken with the
piezometer exposed to the open air.
CAUTION: D
O NOT SUBMERGE THE INSTRUMENT IN WATER TO TAKE THE INITIAL
READINGS
. O
NLY ATMOSPHERIC PRESSURE SHOULD BE APPLIED TO THE PIEZOMETER
AT THIS TIME
. F
AILURE TO DO SO MAY IMPACT THE ACCURACY OF THE SUBSEQUENT
READINGS
.
The temperature reading from the internal thermistor must also be recorded. The
barometric pressure for piezometers with a total range lower than 2 MPa must also
be recorded. These values are needed to apply the correct correction factors for
changes in temperature and/or barometric pressure, which will impact the reading
accuracy of the vibrating wire piezometers through their intended range.
Initial zero readings are generally obtained immediately prior to installation with no
external pressure and a constant ambient temperature and barometric pressure.
NOTE: B
E SURE TO RECORD THE VIBRATING WIRE PIEZOMETER TEMPERATURE AND
BAROMETRIC PRESSURE AT THE SAME TIME THE
B-U
NIT ZERO READINGS ARE
TAKEN
.
The following checks are required to obtain accurate initial zero readings:
•
Has the temperature of the vibrating wire piezometer body reached full thermal
equilibrium?
◼
Variations in temperature across the mass of the piezometer body may result
in a temperature reading which is not consistent with the entire vibrating wire
instrument. This inconsistency will result in an error to the calculated pressure
being read by the vibrating wire sensor. Allow 20 to 30 minutes for the
temperature of the vibrating wire piezometer to equilibrate. Sources of
temperature fluctuation, such as water flow, may have to be eliminated.
•
Is the filter stone saturated?
◼
Surface tension effects within the pore spaces of the filter could affect the
zero readings if the filter stone is only partially saturated. This can be a
problem particularly at low pressures (less than 350 kPa). Remove the filter