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Power supply
the total allowable number of sensors within a concurrent
measurement group.
See the
SDI-12 for GP2 User Manual
for more information on
using groups with concurrent measurements to prevent network
power supply overloading.
Maximum cable length
See page 14
Data communication and measurement
durations
The time taken for SDI-12 commands to be sent by the logger
and for measurement results to be reported back by the
WET150 forms a large part of the overall measurement time.
This is due to the communication speed required by the SDI-12
specification.
Commands sent by loggers and responses sent by SDI-12
sensors are variable in length (and therefore transmission time).
As an indication, a standard three-parameter W-E-T reading on
a WET150 has the following typical durations:
•
From start of SDI-12 measurement command to finish of
SDI-12 data ready service request command (including
active sensing and results computation): 360ms
•
From start of SDI-12 data request command to finish of
SDI-12 measurement data transmission: 240ms
SDI-12 communication interface
The WET150 is compliant with version 1.3 of the SDI-12
specification. In addition, the data port is protected from mis-
wiring to Power or Ground.
Output High and Low data states (dependent on network
loading)
High: Typical 5V
Low: Typical 0V
Input High and Low data state requirements (relative to Ground
voltage at the sensor)
High: Typical 5V (minimum 3.5V)
Low: Typical 0V (maximum 1.5V)
