Civil Engineering Reference
In-Depth Information
4.2.2 Instrumentation Details
4.2.2.1 Vibrating Wire Displacement Transducers (VW)
The VW displacement transducer uses a vibrating wire to detect displacements,
and can be used to monitor the movement of joints or cracks in structures.
Anchors are installed on opposite sides of the joint and the transducer is mounted
across the anchors. When movement occurs in the joint, a change in the distance
between the anchors induces a variation in the frequency signal produced by the
transducer when excited by the readout device. The readout device processes the
signal, applies calibration factors, and displays a reading in the required
engineering units. Displacement is calculated by comparing the current reading to
the initial reading.
Locations
:
Clusters of VW transducers (also known as jointmeters or
crackmeters) were mounted at four locations across the expansion joint separating
PG-1 and PG-2. Each cluster contained two transducers (Fig. 4.5) measuring
movement parallel and perpendicular to the joint. The clusters were mounted on
the underside of the third and roof level slabs (Levels B & D), with one cluster on
each of the northern and southern sides of the joint at each level.
Fig. 4.5
Photograph of VW-Transducer Cluster
Specifications
:
The VW displacement transducers used in the instrumentation
have a measuring range of 100 mm (4 in), with a resolution of 0.025% of full
scale, or 0.025 mm, and a precision is
0.5 mm. The
transducers minimum and maximum lengths are 375 mm (14.75 in) and 475 mm
(18.75 in) respectively. They are also equipped with a built-in temperature sensor
±
0.5% of full scale or
±
