Geokon 4425, Instruction Manual, Page: 7 / 27

1
1. INTRODUCTION
The Model 4425 Vibrating Wire Convergence
Meter is designed to detect the deformation of
rock or soil masses by measuring the contraction
(or elongation) between two fixed anchor points.
Anchor points are established in the mass, and
connecting rods from one anchor lead back to
transducer assembly located at the second anchor
point. Changes in distance between the two
anchors are conveyed by the connecting rods and
measured by the transducer.
The Model 4425 Convergence Meter consists of
three basic components: the two anchor points, 6
mm (1/4") diameter connecting rods, and the
spring-tensioned vibrating wire transducer
assembly. (See Figure 1.) Essential accessories
include: A vibrating wire readout and an
installation tool kit (supplied).
The transducer consists of a vibrating wire sensing
element in series with a heat treated, stress
relieved spring which is connected to the wire at
one end and a connecting rod at the other. The
unit is fully sealed and operates at pressures of up
to 250 psi. As the connecting rod is pulled out
from the gauge body, the spring is elongated
causing an increase in tension, which is sensed by
the vibrating wire element. The tension in the wire
is directly proportional to the extension, so the
convergence can be determined very accurately by
measuring the strain change with the vibrating
wire readout box.
The convergence meter can operate in horizontal,
inclined, or vertical orientations. In areas where
construction traffic is expected or where the
instrument may be left in an exposed location,
some form of protective housing should be
considered.
Turnbuckle
Eye Hook
Swagelok Fitting
Thermistor
Spring
Transducer Shaft
Connecting Rod
Electromagnetic Coil
Instrument Cable
Swagelok Fitting
Eye Hook
Alignment Slot & Pin
Transducer Housing
Swagelok Fitting
Left-Hand Thread
Right-Hand Thread
Figure 1 - Model 4425 Convergence Meter