Xylem WL400 WATER LEVEL SENSOR - Manual (Page 5)

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g. 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 5.00volts DC. If the 4-20 mA signal is dropped
across a 125 ohm resistor, the output will be halved to 0.5 to 2.50
VDC. The resistor is placed between this input and the ground
terminal of the data logger’s battery. The optional temperature output
produces a 0-10mA output current, generating either 0-2.50 volts or 0-
1.25 volts depending on the resistor selected.
h. The sensors may be manually pulsed on or turned on by the logging
system prior to taking a reading. Use a warm up time appropriate to
the water Level sensor being used to assure that the sensor is fully on.
The sensors can run continuously for real time applications. Each
sensor draws between 4 and 20mA depending on whether the sensor
is reading at the minimum or maximum of its range. The optional
temperature output will draw additional current up to the maximum
10mA.
Groundwater
i. The sensor may be suspended in a 2” monitoring well near the well
screen.
Surface Water
j. The sensor may be submerged at the monitoring point and hung from
its cable. It is recommended to protect the sensor inside a 4” PVC
drainpipe that will act as a protective stilling well. Put a cap on the
bottom end of the pipe to allow easy water flow past the sensors.
Drop the sensor until it touches the bottom of the stilling well and then
pull it up slightly and secure the cable.
Sewer Flow Option
k. The WL400 Sewer Pipe Flow Option includes a level sensor built into
a protective “mouse” housing and attached to a 12” stainless steel