Geokon 6350, Installation Manual, Page: 20 / 26

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3.4 MICRO-10 Datalogger
The following parameters are recommended when using the Model 6350 with the MICRO-10
datalogger or any other CR10 based datalogger:
3.4.1 Excitation
The 2.5V excitation directly off the wiring panel is ideal for these sensors. The five volt
supply from the AVW-1 and AVW-4 modules is also usable, but the 12V excitation
should be avoided as it tends to overdrive the sensor. The default excitation voltage used
in MICRO-10 systems is 5V.
3.4.2 Excitation Frequency
The starting and ending frequencies of the excitation sweep should be kept in a relatively
narrow band for these sensors to maximize the stability and resolution of the output. The
exact values can be calculated for a given sensor from the supplied calibration report.
Ideally, the settings should be calculated by taking an initial reading and then setting the
starting frequency to 200 Hz below and the ending frequency 200 Hz above. Alternately,
the low-end frequency sweep setting should be set to 14 (1400 Hz), the high end, 35
(3500 Hz).
3.5 Measuring Temperatures
All vibrating wire piezometers are equipped with a thermistor, which gives a varying resistance
output as the temperature changes. The white and green leads of the instrument cable are
normally connected to the internal thermistor.
The GK-403, GK-404, and GK-405 readout boxes will read the thermistor and display the
temperature in degrees C.
To read temperatures using an ohmmeter:
1) Connect an ohmmeter to the green and white thermistor leads coming from the strain gage.
(Since the resistance changes with temperature are large, the effect of cable resistance is
usually insignificant. For long cables a correction can be applied, equal to 14.7
Ω
per 1,000
feet or 48.5
Ω
per km, multiply this factor by two to account for both directions.
2)
Look up the temperature for the measured resistance in Appendix C, Table 4.