1Application
Model VWP Vibrating Wire Piezometer is applicable to be embedded in hydraulic and other concrete or soil structures to measure the penetrated fluid pressure. Meanwhile, the temperature value of the embedding point can also be measured. By adding accessories, the piezometer can be used for situations like pressure measuring of tunnels, boring for foundation, etc. The piezometer is structured with stainless steel and a dimension of 24x120mm. It can be easily located in narrow and small positions or places. And this piezometer has intelligent identification function..
2Technical Specifications

VWP0.16

VWP0.25

VWP0.4

VWP0.6

VWP1

VWP2.5

VWP3

Size

Outer Diameter D (mm)

24

Length L (mm)

120


Measurement Range (KPa)

0～160

0～250

0～400

0～600

0～1000

0～2500

0～3000

Performance

Sensitivity k (KPa/F)

≤0.072

≤0.11

≤0.18

≤0.27

≤0.45

≤1.13

≤1.35

Accuracy (F.S)

±0.1%

Temp.^{ 1} Measure.^{ 2} Range (℃)

40～+150

Temp. Measure.^{ }Accuracy(℃)

±0.5

Temp. Correct.^{ 3 }Co.^{4} b (KPa /℃)

≈0.12

绝缘电阻 P Water Pressure Resistance (MPa)

1.2 times Measurement Range

Insulation Resistance (MΩ)

≥50

Remark: Frequency Modulus F= Hz^{2}×10^{3}
^{1}: Temperature
^{2}: Measurement
^{3}: Correction
^{4}: Coefficient
3The Theory of Operating
3.1 Constitution
Model VWP Vibrating Wire Piezometer consists of permeable component, induction film, sealed enclosure, signal transmission cable, vibrating wire, excited electromagnetic coil, etc.
3.2 Mechanism
The fluid pressure will generate the deformation of the elastic film. The deformation will be transferred to vibrating wire and to change to be the changing of the strain. Thus, the vibrating frequency of the vibrating wire is changed. The electromagnetic coils excite the vibrating wire and measure the vibrating frequency. The frequency signal is transferred to readout device via the cable. And as the result the pressure value of the fluid load can be obtained. Meanwhile, the temperature value of the embedding point can be measured at the same time.
3.3 Calculation
a)The pressure value P has a linear relationship with the output frequency modulus △F as the gauge is bearing the penetrated fluid pressure under environmental temperature as constant:
P= k△F
△F = F  F_{0}
where,
k: Sensitivity with the unit of KPa/F;
△F: Difference between the measured realtime value and the reference one with the unit of F;
F: Realtime measured value with the unit of F;
F_{0}: Reference value with the unit of F.
b)When the penetrated fluid pressure is constant, there is an output value △F´ if the temperature is increased by △T. This output is only caused by the changing of the temperature, thus it should be deducted in calculation.
Experiment shows that △F´ and △T has the following linear relationship:
P´= k△F´+ b△T = 0
k△F´= b△T
△T = T  T_{0}
where,
b: Temperature correction coefficient with the unit of KPa/℃;
△T: Difference between the measured realtime value and the reference one with the unit of ℃;
T: Realtime measured temperature value with the unit of ℃;
T_{0}: Reference temperature value with the unit of ℃;
c)When the gauge is subject to the effects from penetrated fluid pressure and the temperature, it should be corrected if the atmospheric pressure is fairly changed. Thus, the general calculation formula is:
Pm = k△F + b△T = k (F_{0 } F) + b(T  T_{0}) + (Q_{0}Q)
where,
Pm: Strain value of the measured structure with the unit of MPa;
Q_{0: }Reference measured value with the unit of KPa;
Q: Realtime measured value with the unit of KPa;
Meter water column (Unit of pressure) = KPa/9.81 