ELPRO 905U - Page 20

905U Wireless I/O Module User Manual
105S Serial I/O Module
Page 20 © January 2011
The positive terminal ("AI 1+" or "AI 2+", etc) should be connected to "+24V".
Externally powered loops may be connected by connecting the input between "AI 1+" and “AI 1-” for
analog input 1 or "AI 2+" and “AI 2-” for analog input 2, and so on for other inputs. Common mode
voltage may be -0.5V to 27V.
Shielded cable is recommended for analog I/O loops to minimise induced noise and Radio Frequency
Interference (RFI). The shield of the cable should be connected to earth at one of the cable only. The
use of shielded wiring inside an enclosure containing a module is also recommended.
To connect an AI on the 905U to an analog signal from a PLC or DCS output, check the internal
circuit of the output carefully as different devices use different ways to create an analog signal. The
following diagram shows two ways of connecting.
AO
PLC
_
+24V
+AI
- AI
COM
905U
+24V
+AI
- AI
COM
905U
Current
source
output
Note:
1. AI must be
within 27V of COM.
If terminal voltages
exceed this, a loop
isolator must be
used.
2. COM on the
105U is connected
to ground/earth. If
the COM of the
PLC cannot be
grounded, then a
loop isolator must
be used.
+
+
V
-
V
AO
COM
PLC
Current
sink
output
4-20mA
+
_
+24V
+AI
- AI
COM
905U
2-wire
Input
+
_
+24V
+AI
- AI
COM
905U
4-wire
Input
External
Power
Note:
AI must be within
27V of COM. If
terminal voltages
exceed this, a
loop isolator must
be used.