1Application
Model VWD-B Vibrating Wire Bedrock Displacement Meter is applicable to measure the extension/deformation between hydraulic structures or other concrete structures and the base foundations. At the same time the displacement meter is also able to measure the temperature value of the embedding point. The displacement meter is equipped with Model VWD Vibrating Wire Displacement Transducer and accessories. And this Displacement Meter has the intelligent identification function..
2Technical Specifications
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VWD-20B
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VWD-50B
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Measurement Range (mm)
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0～20
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0～50
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Sensitivity k (mm/F)
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≤0.01
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≤0.02
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Accuracy (F.S)
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±0.1%
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±0.1%
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Temperature Range (℃)
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-40～+150
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-40～+150
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Temperature Resolution (℃)
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±0.5
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±0.5
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Outer Diameter (mm)
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30.5
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30.5
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Length (mm)
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300
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340
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Water Pressure Resistance (MPa)
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≥1
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≥1
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Insulation Resistance (MΩ)
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≥50
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≥50
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Remark: Frequency Modulus F= Hz2×10-3
3Theory of Operation
3.1 Constitution
Model VWD-B Vibrating Wire Bedrock Displacement Meter consists of back stand, length rod, protecting shield, installation stand, rock bolt, cables, vibrating wire and exciting electromagnetic coils.
3.2 Mechanism
The variation of the displacement meter will be brought as there is extension/deformation generated between the structures and base foundations. Thus, this variation is transferred to the vibrating wire via the rock bolt and back stand in order to generate the strain variation. Thereby, the oscillating frequency of the vibrating wire is changed as the consequence. The electromagnetic coils stimulate the vibrating wire and measure the oscillating frequency. As the result, the frequency signal is transmitted via the cable to the readout device and the deformation value of the measured structure is thereby obtained.
3.3 Calculation
The deformation value J has a linear relationship with the output frequency modulus △F as the displacement meter is bearing the axial deformation under outside environmental temperature as constant:
J = k△F
△F = F - F0
Herewith,
k: Sensitivity with the unit of mm/F;
△F: Difference between the measured value and the reference one with the unit of F;
F: Measured value with the unit of F;
F0: Reference value with the unit of F.
When the Displacement Meter 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:
J´= k△F´+ b△T = 0
k△F´= -b△T
△T = T - T0
Herewith,
b: Temperature correction coefficient with the unit of mm/℃;
△T: Difference between the measured value and the reference one with the unit℃;
T: Real-time measured temperature value with the unit of ℃;
T0: Reference temperature value with the unit of℃;
The displacement meter settled in the hydraulic or other concrete structures is subject to the effects of deformation and temperature. The general calculation formula is:
Jm = k△F + b△T = k (F - F0) + b (T - T0)
where,
Jm: The deformation value of the measured structure with the unit of mm;
Remark:
The Displacement Meter has the automatic temperature compensation. Experiment shows that the temperature correction coefficient is smaller than the minimal reading value, and the calculation formula a) is applicable for general situation. |
