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1. INTRODUCTION
The Geokon Model 4000 Vibrating Wire Strain Gage is intended primarily for long-term or
short term strain measurements on structural steel members such as tunnel linings, arches,
struts, piles, sheet piling, etc.
The primary means of attachment is by conventional arc welding, but they may also be used
to monitor strain changes on concrete or rock surfaces using anchors grouted into
boreholes.
Strains are measured using the vibrating wire principle: a length of steel wire is tensioned
between two mounting blocks that are welded to the steel surface being studied.
Deformations (i.e., strain changes) of the surface will cause the two mounting blocks to
move relative to one another, thus altering the tension in the steel wire. The tension in the
wire is measured by plucking the wire and measuring its resonant frequency of vibration.
The wire is plucked, and its resonant frequency measured, by means of an electromagnetic
coil positioned next to the wire. See Figure 1.
Figure 1 - Model 4000 Vibrating Wire Strain Gage
Portable readouts available from Geokon, used in conjunction with the Vibrating Wire Strain
Gage, will provide the necessary excitation to pluck the wire and will convert the measured
frequency so as to display the reading directly in microstrain.
This manual contains installation instructions, readout instructions and recommended
maintenance and troubleshooting procedures. The theory of the gage is also given, along
with some suggestions for data interpretation.
Protective Tube
Instrument Cable
Pluck & Read Coils
Thermistor
Wire
Coil & Thermistor Housing
Mounting Block
Wire Grip
Wire Grip
(4 conductor, 22 AWG)
Gage Length
(6
.500", 165
mm)
Mounting Block
O-ring Sealed End Block
Set Screw
Set Screws (2 places)
(cone point)
(cone point)
