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1. INTRODUCTION
The Geokon Model 4200ER Vibrating Wire Strain Gage is designed primarily for high range
strain measurements in mass concrete, in structures such as foundations, piles, bridges,
dams, containment vessels, tunnel liners, etc. See Figure 1. Strains as high as 10,000
mirostrain can be accomodated
Figure 1 - Model 4200ER Vibrating Wire Strain Gage
Note the small collar under the shrink tube at one end.
The primary means of gage placement is direct embedment in concrete by pre-attaching the
gage to rebar or tensioning cables, pre-casting the gage into a concrete briquette which is
subsequently cast into the structure, or grouting 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 relative to one another, 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. Electromagnetic coils that are located close to the wire
accomplish excitation and readout of the gage frequency.
Portable readouts or dataloggers available from Geokon, such as the model, GK-403, GK
404 or MICRO-6000 datalogger, used in conjunction with any of these vibrating wire strain
gages, will provide the necessary voltage pulses to pluck the wire and convert the measured
frequencies so as to display the reading directly in digits which can then be converted into
microstrain using the calibration coefficients supplied.
This manual contains installation instructions, readout and data reduction procedures, and
troubleshooting guidelines.
PLEASE NOTE THE FOLLOWING:
Do not rotate or pull on the gage end blocks as this will alter the readings and may
cause permanent damage.
