sensors

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

Rugged vibrating wire meter specifically designed for embedding in mass concrete to monitor construction joints.

Measuring Range
15, 25, 50 mm
Accuracy
±0.1% F.S.
Resolution
0.025% F.S.

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Overview

Rugged vibrating wire meter specifically designed for embedding in mass concrete to monitor construction joints.

The Geolook Vibrating Wire Joint Meter is a robust instrument engineered to monitor the opening and closing of construction joints in mass concrete structures. Unlike surface-mounted crack meters, this sensor is designed to be embedded directly within the concrete block, making it integral to the structure itself. It is particularly suited for monitoring the interface between concrete lifts in arch dams, abutments, and other massive civil engineering works. The sensor body is constructed from high-strength stainless steel to withstand the pressures of concrete placement and curing while providing stable, long-term data on joint behavior.

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Benefits & Features

  • Designed for direct embedment in mass concrete
  • High-strength stainless steel construction
  • Accommodates shearing motion at the joint
  • Vibrating wire technology for long-term stability
  • Integral thermistor for temperature compensation
  • Frequency signal immune to cable length
  • Waterproof to 2 MPa pressure
  • Available in uni-axial and tri-axial configurations

Detailed Description

What is a VW Joint Meter?

A Vibrating Wire (VW) Joint Meter is a specialized displacement sensor designed to measure the relative movement between two adjacent concrete blocks. Unlike a crack meter which bridges an existing surface fissure, a joint meter is typically installed across a planned construction joint before or during the concrete pouring process.

Its primary function is to monitor the 'opening' (expansion) or 'closing' (contraction) of the joint. This data is critical for verifying that the structure is behaving as designed, particularly during the initial curing phase and subsequent thermal cycles.

Why use Vibrating Wire Technology?

In the harsh environment of mass concrete—where sensors are permanently buried and inaccessible—reliability is paramount. Vibrating wire technology offers significant advantages over resistive or voltage-based sensors:

  • Zero Drift: VW sensors maintain their calibration over decades, essential for the 50-100 year lifespan of a dam.
  • Signal Integrity: The frequency output signal does not degrade over long cable runs (up to 2km), allowing readout stations to be located far from the sensor.
  • Moisture Resistance: The sensor is hermetically sealed and its signal is unaffected by moisture ingress in the cable.

How does it work?

The VW Joint Meter consists of two main parts: a socket (anchored in the first concrete block) and the sensor body (anchored in the second, adjacent block). As the joint opens or closes, a sliding shaft within the sensor moves, changing the tension of an internal steel wire.

An electromagnetic coil plucks this wire, causing it to vibrate at a frequency proportional to the tension. This frequency is measured by a readout unit and converted into millimeters of displacement. The design typically includes a bellows or protective housing to allow the sensor to accommodate some shearing motion (movement perpendicular to the sensor axis) without being damaged.

Typical Applications

  • Dam Safety: Monitoring the critical contraction joints in arch dams to ensure proper load transfer between blocks.
  • Bridge Engineering: Verifying the performance of expansion joints in bridge decks and piers.
  • Tunnel Linings: Measuring the convergence or separation of segmental concrete tunnel linings.
  • Foundations: Monitoring the interface between a massive concrete foundation and the bedrock or adjacent structures.

Installation & Durability

Installation typically involves grouting the socket component into the first concrete lift. Once that concrete has set, the sensor body is screwed into the socket before the second lift is poured. This ensures a rigid connection across the joint.

Constructed from corrosion-resistant stainless steel and rated to withstand high hydrostatic pressures (up to 2 MPa), the Geolook G71-V260 is built to survive the aggressive chemical and physical environment of curing concrete.

Available Models

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Specifications

Measuring Range
15, 25, 50 mm
Accuracy
±0.1% F.S.
Resolution
0.025% F.S.
Operating Temperature
-20°C to +80°C
Housing Material
Stainless Steel
Pressure Rating
2 MPa (Waterproof)
Thermistor
YSI 44005 or equivalent (3kΩ @ 25°C)
Cable
4-core shielded armored cable