Sentek RT6, Hardware Manual

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CHAPTER 3: TECHNICAL DESCRIPTION
Page 19
Chapter 3: Technical Description
General System Operation
Sampling
Signal from sensor
to logging facility
Signal
measurement
Between sampling only the necessary circuitry of the
logging facility is powered while it waits for the next
sampling period. No power is applied to the probe
cabling or probes between sampling.
During sampling the Sentek RT6 logger applies
power to the probe cabling (and probes) and a signal
to power up (address) a particular sensor. The address
signal is processed by the probe interface (5-wire
board) which applies power down one of the wires of
the ribbon cable on the probe. The sensor that has
been addressed (via PCB link) picks up the power
from the ribbon cable and begins to oscillate at a
frequency depending on moisture content of the soil.
The signal from the sensor (open collector 40 to 80
kHz) is applied to a common wire on the probe
ribbon cable back to the interface board.
The 5-wire interface board converts the signal from
open collector to differential drivers for transmission
back to the logger via probe cabling.
After addressing the sensor the logger waits for 0.5
seconds (while sensor stabilizes) then counts pulses
for 0.5 seconds and records the reading in the
removable loggers memory with a time/date stamp.
The logger then sends a signal to power up (address)
the next sensor (while turning off previous sensor)
and repeats the process. Once all sensors have been
recorded the logger removes power from the probes
and waits for the next sampling interval.
Detailed technical description
Logging facility
The logging facility is capable of reading and storing
data from multiple sensors at pre-selected sampling
intervals ranging from 1 minute to 9999 minutes (i.e.