sensors

VW Crack Meter (1D / 2D / 3D)

Precision crack meter for monitoring joint and crack movements in concrete structures using vibrating wire technology.

Measuring Range
12.5, 25, 50, 100 mm
Accuracy
±0.1% F.S.
Resolution
0.025% F.S.

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Overview

Precision crack meter for monitoring joint and crack movements in concrete structures using vibrating wire technology.

The Geolook Vibrating Wire Crack Meter is designed for long-term monitoring of crack width changes and joint movements in concrete, masonry, and rock structures. It provides highly accurate, stable measurements essential for assessing structural integrity over extended periods. The sensor features a robust stainless steel construction with mounting anchors for easy installation across cracks or joints. The vibrating wire transducer ensures excellent long-term stability with minimal maintenance, making it ideal for inaccessible areas or harsh environments.

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Benefits & Features

  • High accuracy displacement measurement (±0.1% F.S.)
  • Robust anchor mounting system (Groutable or Expansion)
  • Vibrating wire technology for long-term stability
  • Integral thermistor for temperature compensation
  • Suitable for concrete, masonry, and rock surfaces
  • Frequency output signal unaffected by cable length
  • Hermetically sealed construction (IP68)
  • Long service life exceeding 20 years

Detailed Description

What is a Vibrating Wire Crack Meter?

A Vibrating Wire Crack Meter is a displacement sensor specifically designed to measure the widening or closing of cracks and joints on structural surfaces. It consists of a sensor body and a target (or two anchors) installed on opposite sides of a fissure.

As the distance between the anchors changes due to structural movement, the tension in the internal wire changes. This change in tension alters the wire's resonant frequency, which is measured by a readout unit or datalogger and converted into millimeters of displacement.

Advantages of Vibrating Wire Technology

  • Long-Term Stability: Zero drift is negligible compared to potentiometric or LVDT sensors.
  • Durability: No moving parts (like sliding wipers) means less wear and tear.
  • Cable Independence: Signal accuracy is not affected by moisture or cable resistance changes.
  • Temperature Compensation: An integrated thermistor allows for the correction of thermal expansion effects on the structure.

How does a Vibrating Wire Crack Meter work?

A vibrating wire crack meter operates on the principle that the resonant frequency of a tensioned wire changes when the tension in the wire changes. The instrument typically consists of a sensor body containing a stretched magnetic steel wire and a spring mechanism, which is anchored across a crack or joint.

As the crack opens or closes, the relative movement between the anchors causes a change in the tension of the internal wire. If the crack widens, the tension increases; if it closes, the tension decreases. This physical change is directly proportional to the displacement being monitored.

To take a measurement, an electromagnetic coil within the sensor plucks the wire, causing it to vibrate at its natural resonant frequency. This frequency is then detected by the coil and transmitted to a readout unit or datalogger. The readout converts the frequency signal into a precise displacement measurement (typically in millimeters) using calibration factors specific to the sensor.

Since the output is a frequency signal rather than a voltage or resistance change, the data is immune to electrical noise and cable resistance effects. This makes vibrating wire crack meters exceptionally stable and reliable for long-term monitoring over long cable distances.

Application of Vibrating Wire Crack Meter

  • Monitoring of surface and embedment cracks in concrete structures such as dams, spillways, and intake towers.
  • Measurement of expansion and contraction joint movements in bridges, flyovers, and aqueducts.
  • Long-term structural health monitoring of historical monuments and heritage buildings for preservation.
  • Observation of joint opening in tunnel linings, underground caverns, and subway stations.
  • Monitoring displacement across geological faults and rock fractures in slope stability projects.
  • Assessment of structural integrity in nuclear power plants and other critical infrastructure.
  • Monitoring crack propagation due to thermal changes, foundation settlement, or load redistribution.
  • Verification of structural performance during load testing and construction phases.

Available Models

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Specifications

Measuring Range
12.5, 25, 50, 100 mm
Accuracy
±0.1% F.S.
Resolution
0.025% F.S.
Operating Temperature
-20°C to +80°C
Housing Material
Stainless Steel 316L
Anchor Type
Groutable (standard) or Expanding Shell
Thermistor
YSI 44005 or equivalent (3kΩ @ 25°C)
Protection Rating
IP68