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3 COLLECTING DATA

3.2

Data Logger Requirements

The LWS works with Decagon's 5-channel Em50 or Em50R data log-

gers. It can also be adapted for use with other data loggers, such as

those from Campbell Scientiﬁc, Inc. (See Appendix A for a sample

program.) The sensor requires an excitation voltage in the range of

2.5 to 5 volts.

It produces an output voltage that depends on the dielectric con-

stant of the medium surrounding the probe, and ranges between 10

to 50% of the excitation voltage. Any data logger which can produce

a 2.5 to 5 V excitation with approximately 10 millisecond duration

and read a volt level signal with 12-bit or better resolution should

be compatible with the LWS. The current requirement at 2.5 V is

around 2 mA, and a 5 V it is 7 to 8 mA.

Note: The LWS is intended only for use with data loggers and readout

devices which can provide short excitation pulses, leaving the probes

turned oﬀ most of the time. Continuous excitation not only wastes

battery power, but may, under certain circumstances, cause the probe

to exceed government speciﬁed limits on electromagnetic emissions.

3.3

Adapter Cable Wiring

If you use a non-Decagon data logger, clip the stereo plug oﬀ and

connect the lead wires directly to the chosen logger. The wiring con-

ﬁguration is shown below.

White = Power 2.5 to 5 V excitation

Bare shield = Ground

Red = Sensor data output (single ended)

LWS