Xylem WE100 BAROMETRIC PRESSURE TRANSMITTER - Manual (Page 4)

Global Water
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III. General Sensor Installation
a. Weather sensors have many applications and therefore many
installation options. The sensors should be located in a clear area on
a level surface.
b. Install your Weather sensor so that it is easily accessible for calibration
purposes. You may need to remove and reinstall it in the future, so
plan ahead!
c. All Global Water Weather sensors produce a 4-20 mA output signal.
4-20 mA is an industrial standard signal for process control monitoring.
Most PLCs (Programmable Logic Controller), RTUs (Remote
Telemetry Unit), and data acquisition systems accept this signal
directly. If the system only accepts voltage signals, the sensor output
must be converted to a voltage signal by reading the voltage across a
precision resistor in series with the signal wire. Since Ohms Law
states that V = IR, if the 4-20 mA signal is dropped across a 250 ohm
resistor, the output will be 1 to 5 volts DC. If the 4-20 mA signal is
dropped across a 125 ohm resistor, the output will be halved to 0.5 to
2.5 VDC. The 4-20 signal wire is connected to the datalogger voltage
input terminal. The resistor is placed between this input and the
ground terminal of the datalogger’s battery. The power (or voltage to
the sensor) must be connected to positive battery terminal of the
datalogger.
d. The sensors may be pulsed on or turned on by the logging system
prior to taking a reading. Use a warm up time appropriate to the
Weather sensor you are using to assure that the sensor is fully on.
The sensors can run continuously for real time applications. Each
sensor draws between 4 and 20 mA depending on whether the sensor
is reading at the minimum or maximum of its range.
e. Weather sensors may be stored without any special provisions. Place
the sensor inside a bag to keep the sensor clean and store on a shelf
or hang it on a wall.