Introduction; Figure 1: On-Site Installation Photo - Geokon 4200 Series Instruction Manual

1.

INTRODUCTION

vibrating wire embedment strain gauges are designed for direct
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embedment in concrete. This can be accomplished by attaching the gauge to
rebar or tensioning cables and then casting the gauge into a concrete briquette,
which is subsequently cast into the structure, or grouting the gauge into
boreholes in the concrete.
Strains are measured using the vibrating wire principle. A length of steel wire is
tensioned between two end blocks that are firmly in contact with the mass
concrete. Deformations in the concrete will cause the two end blocks to move in
relation to each other, altering the tension in the steel wire. This change in
tension is measured as a change in the resonant frequency of vibration of the
wire.
Two coils, one with a magnet insert, the other with a pole piece insert, are
located close to the vibrating wire. In use, a pulse of varying frequency (swept
frequency) is applied to the coils causing the wire to vibrate primarily at its
resonant frequency.
Portable readouts and dataloggers are available from . These models,
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when used in conjunction with vibrating wire strain gauges, will provide the
necessary voltage pulses to pluck the wire. During vibration, a sinusoidal signal
is induced in the coils and transmitted to the readout box where it is conditioned
and displayed.
This manual contains installation instructions, readout and data reduction
procedures, and troubleshooting guidelines.
Note: Do not rotate or pull on the gauge end blocks, because this will alter the
readings and may cause permanent damage.

FIGURE 1: On-site Installation Photo

MODEL 4200 SERIES STRAIN GAUGES | INTRODUCTION | 1