User's Manual

905U-L Wireless I/O Installation Manual
905U-L Wireless I/O Page 26 of 40
Version 1.9
Analog input
The 905U-L-T module provides one 0 - 20 mA DC analog input for connecting to
instrument transducers (e.g. level, moisture, pressure transducers, etc.).
Note
The 905U-L-T module inputs measure down to 0mA and can also be used for zero based
signals (e.g. 0 - 10 mA).
The analog input has a positive and negative terminal and can be placed at any point in
the current loop, providing neither input rises above the 24 volt Analog Loop Supply
level.
Each input has a loop resistance of less than 250 ohms and zener diode protection is
provided against over-voltage and reverse voltage.
Note
You may require additional protection in high voltage or noisy environments or for long
wiring runs.
A 24VDC loop supply is available on the 905U-L-T module for powering the analog
transducer loops. In this situation, connect the:
 Analog loop - between an Analog Input (-) terminal and Ground.
 Positive terminal – i.e. Analog Input (+) to the +24V Analog Loop Supply.
Externally powered loops may be connected by connecting the input between "Analog
Input (+)" and “Analog Input (-)” Common mode voltage may be -0.5V to 27V.
ELPRO recommends using shielded cable for analog I/O loops to minimize induced noise
and Radio Frequency Interference (RFI).
Note
You should only connect one end of the cable shield to Earth
To connect an analog signal from a PLC or DCS output to an analog input on the 905U-L-
T, you must carefully check the internal circuit of the output as different devices use
different ways to create an analog signal.