1. Theory of Operation
The theory of operation is described in the Model 4700 brochure.
2. Installation
The Model 4700 Vibrating Wire Temperature Sensor can be installed inside boreholes, buried in fill, or cast
inside concrete. They are fully waterproof. No particular requirements are needed. Preliminary readings should be
taken to ensure that the sensor is functioning properly. Most models incorporate a thermistor that can be used as a
check on the vibrating wire readout.
3. Readout Procedures
Connect the black and red leads to the GK-401, GK-403 or GK-404 VW Readout Box and read on channel B. If
the GK-403 Readout Box, GK 404 Readout Box or Micro-10 Datalogger is used, the thermistor readout can be
displayed directly in
°
C. If a GK-401 Readout Box is used, the thermistor can be read on the green and white
conductors using a digital ohmmeter in conjunction with the conversion Table in Appendix A. Allowance for
cable resistance may be necessary (22 gage cable has a resistance of 20
Ω
/300 meters).
4. Data Reduction
The temperature (
T
) is given by the formula:
T = G (R
0
–R
1
)
in degrees centigrade
Where:
R
0
is the initial reading on channel B at 0
°
C
R
1
is the subsequent reading on channel B
G
is the gage factor
A typical calibration sheet showing the gage factor is given on page 3.
5. Trouble Shooting _______________________________________________
Maintenance and trouble shooting of vibrating wire temperature sensors are confined to periodic checks of cable
connections and maintenance of terminals. The transducers themselves are sealed and cannot be opened for
inspection.
•
A normal resistance between black and red conduction is 180
Ω
± 5
Ω
plus cable resistance (20
Ω
/300m).
•
A normal resistance between white and green conduction depends on the temperature (see table on page 4).
If the resistance deviates from the norms, inspect the cable for damage.