1Application
Model VWS Vibrating Wire Strain Gauge is applicable to be embedded in hydraulic and concrete geotechnical structures to measure the inner strain value of the structure. Meanwhile, the temperature of the embedding point can be measured. With adding accessories, it can be constituted to be the Multiple Direction Strain Gauges Set, NonStressmeter, Rock Strain Gauge and so on instruments that measure the strain. The strain gauge with a larger modulus of elasticity is mainly used for the continuously cementing of the concrete from high position, e.g. underground diaphragm wall, impervious wall, castinplace pile, etc engineering situations. And this Strain Gauge has the intelligent identification function.
2Technical Specifications

VWS10

VWS15

VWS10M

VWS15M

Size Parameters

Gauge Length L (mm)

100

150

100

150

Valid Diameter d (mm)

22

22

22

22

End Diameter D (mm)

33

33

33

33


Range

Stretching (10^{6})^{}

1500

1500

1500

1500

Perfor
mance

Compressing (10^{6})

1500

1500

1500

1500

Sensitivity k (10^{6}/F)

≤0.5

≤0.5

≤0.5

≤0.5

Accuracy (F.S)

±0.1%

±0.1%

±0.1%

±0.1%

Temp.^{ 1} Measure.^{ 2} Range (℃)

40～+150

40～+150

40～+150

40～+150

Temp. Measure.^{ }Accuracy(℃)

±0.5

±0.5

±0.5

±0.5

Temp. Correct.^{ 3 }Co.^{4} b (10^{6}/℃)

≈13.5

≈13.5

≈13.5

≈13.5

modulus of elasticity Eg (MPa)

300～800

300～800

800～1500

800～1500

Water Pressure Resistance (MPa)

≥1

≥1

≥2

≥2


Insulation Resistance (MΩ)

≥50

≥50

≥50

≥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 VWS VW Strain Gauge consists of front and rear stands, stainless steel protecting shield, signal transmission cable, vibrating wire and excitation coils.
3.2 Mechanism
When the strain is changed from the inner part of the geotechnical structure then the gauge will sense the deformation synchronously. The deformation transfers to the vibrating wire via the front and rear stands and turns out to be the changing of the strain, thus, the vibration frequency of the vibrating wire is changed. Further, the electromagnetic coils excite the vibrating wire and measure the vibration frequency and the frequency signal is transmitted to the readout device via the cable. As the result, the inner strain value can be measured. Meanwhile, the temperature value of the embedding point can be measured at the same time.
3.3 Calculation
The strain value ε has a linear relationship with the output frequency modulus △F as the gauge is bearing the axial deformation under environmental temperature as constant:
ε= k△F
△F = F  F_{0}
Herewith,
k: Sensitivity with the unit of 10^{6}/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.
When the gauge is not affected by external force (gauge length between both ends is unchanged), 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:
ε´= k△F´+ b△T = 0
k△F´= b△T
△T = T  T_{0}
Herewith,
b: Temperature correction coefficient with the unit of 10^{6}/℃;
△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 ℃;
The gauge settled in the hydraulic or other concrete structures is subject to the effects of deformation and temperature. Then the temperature correction coefficient should be the temperature correction coefficient of the gauge subtracts from the liner expansion coefficient. Thus, the general calculation formula is:
ε_{m }= k△F + b′△T = k (F  F_{0})+ (b α)(T  T_{0})
Herewith,
ε_{m}: Strain value of the measured structure with the unit of 10^{6};
α: Liner expansion coefficient of the measured structure with the unit of 10^{6}/℃.