1
1. INTRODUCTION
Geokon Model 4400 Vibrating Wire Embedment Jointmeters are intended primarily for the
measurement of joint openings between lifts or sections in mass concrete or across fracture
zones in fully grouted boreholes.
The instrument 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. As the connecting rod is pulled out from the gage body, the spring is elongated
causing an increase in tension and a resulting change in frequency of the vibrating wire
sensing element The tension in the wire is directly proportional to the extension, hence, the
opening of the joint can be determined very accurately by measuring the frequency change
with the vibrating wire readout box. The unit is fully sealed and operates at pressures of up
to 250 psi.
Alignment Slot
Alignment Pin
Socket
Socket Thread
Transducer Shaft
Transducer Housing
Tripolar Surge Arrestor
Seal Screw
Coil Assembly
Instrument Cable
16.093"
Gage Connector
Universal Joint
Universal Joint
Gage End Flange
Connector Alignment Pin
Swagelok Fitting
Transducer Wires
(2 places)
Protective PVC Gage Housing
408.8mm
Figure 1 - Model 4400 Vibrating Wire Embedment Jointmeter
In use, a socket is placed in the first lift of concrete and, when the forms are removed, a
protective plug is pulled from the socket. The gage is then screwed into the socket, extended
slightly and then concreted into the next lift. Any opening of the joint is then measured by
the gage which is firmly anchored in each lift. The sensing gage itself, is smaller than the
protective housing, and a degree of shearing motion is allowed for by the use of universal
ball-joint connections on the gage.
A thermistor is also located inside the vibrating wire transducer housing for the measurement
of temperature at the jointmeter location. In addition, a tripolar plasma surge arrestor inside
the housing provides protection for the sensor coils from electrical transients such as may be
induced by direct or indirect lightning strikes.
17.37 “
441mm
