Field Photo: This is a vibrating wire surface-mounted displacement transducer (crack meter), installed vertically across a concrete structural surface.
Upper end: Fixed to a metal base at the top of the wall via a spherical joint (fish-eye universal joint). The base is sealed and fixed to the concrete surface with black structural adhesive (epoxy putty) for waterproofing and seepage prevention.
Middle rod body: A silver stainless steel displacement transducer body with upper and lower double universal hinge structures, enabling automatic self-alignment to avoid measurement errors caused by installation misalignment.
Lower end: Fixed to a metal mounting bracket below, bolted to the bottom of the structural surface.
Signal cable: A black shielded cable is led out from the side of the sensor, coiled for storage, and connected to the data acquisition module.
The entire sensor spans across a structural crack (or two structural joints). When the crack opens or closes, the pull rod undergoes axial displacement, changing the tension of the vibrating wire and outputting a corresponding frequency signal, which is then converted into the change in crack width.
Working Principle of Vibrating Wire Displacement Transducers
Crack opening/closing → Change in distance between the two fixed points → Extension/retraction of the pull rod → Change in steel wire tension.
The natural frequency of the steel wire changes with tension → Frequency value is measured.
The crack opening/closing amount (mm) is calculated using the factory-calibrated "frequency–displacement" relationship.
Core feature: The output is a frequency signal (Hz), not a voltage signal. It is unaffected by cable resistance, contact resistance, or humid environments during transmission, making it suitable for long-distance transmission and long-term outdoor monitoring.
Why Use a Vibrating Wire Solution for Wall Crack Monitoring
Comparison Item | Vibrating Wire Crack Meter | Displacement Sensor | Manual Vernier Caliper Reading |
Measurement method | Frequency output, anti-interference | Voltage/bus output | Manual sequential reading |
Long-term stability | Excellent, with minimal annual drift | Good | Cannot guarantee a consistent reading baseline |
Environmental suitability | Moisture-proof, dust-proof, corrosion-resistant; suitable for underground/tunnels/open-air | Requires additional protection | Highly influenced by human factors |
Automated monitoring | Can be connected to a data logger for remote, unattended operation | Can be connected | Not possible |
Service life | More than 10 years of long-term online operation | Depends on operating conditions | / |
Typical Application Scenarios
Building structural safety monitoring: Monitoring cracks in new building walls and the expansion of cracks in existing buildings.
Tunnel/underground engineering: Long-term monitoring of tunnel lining cracks and surrounding rock deformation in roadways.
Hydraulic dams: Monitoring dam body cracks and the opening/closing of expansion joints.
Foundation pits/slopes: Monitoring deformation of cracks in foundation pit retaining structures and slope surfaces.
Bridge engineering: Long-term health monitoring of cracks in bridge girders and piers.
Project Value
Real-time warning: Automatic alarms are triggered when the crack change rate exceeds the threshold, allowing early prediction of structural safety risks.
Unattended operation: Vibrating wire frequency signals are anti-interference, suitable for long-term online monitoring in environments with weak signals and poor conditions, such as underground areas and tunnels.
Easy installation: Surface-mounted installation requires no grooving or embedding, allowing retrofitting of existing structures without work stoppage.
Domestic alternative: Miran vibrating wire displacement sensors offer better cost performance than imported equivalents and have shorter lead times