User's Manual

Chapter Two Installation
man_905_2.1.doc Page 17
for analogue input 1 or "AI 2+" and “AI 2-” for analogue input 2, and so on for other inputs.
Analogue Input 1 "AI 1+" may also be configured to control a high/low analogue set-point. See
Chapter 4 Configuration for further details.
Common mode voltage may be -0.5V to 27V. Shielded cable is recommended for analogue 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.
2.4.5 Analogue Outputs (-1 and -3)
The -1 module provides two 4 - 20 mA DC analogue outputs for connecting to instrument
indicators for the display of remote analogue measurements. The -3 module provides eight 0 - 20
mA DC analogue outputs. Each analogue output is a "sink" to common.
+
-
A 24VDC supply is available on the module for powering the analogue output loop (max external
loop resistance 1000 ohms). In this case, the analogue loop is connected between a "+24V" terminal
and "AO 1" ( for the first analogue output) or "AO 2" (for the second analogue output), and so on
for the other output signals.
Externally powered loops to 27 VDC may be connected by connecting the output between the
"AO” terminal (positive) and the "COM" terminal (negative). Zener protection of analogue outputs
provides protection against short periods of over-voltage but longer periods may result in module
damage. Note that the common is connected internally to ground and no other point in the
analogue loop should be grounded.
Analogue outputs may also be configured to individually turn off (0 mA) if no command message is
received to that output for a certain period. . See Chapter 4 Configuration for further details.
2.4.6 Pulse Input (-1)
For the -1 module, digital input 1 may be configured as a pulse input (max rate 100 Hz, min. off time
5 ms). In this mode, both the pulse rate and the pulse count are available for mapping to a remote
output. The pulse rate may appear at any analogue output on the remote unit, while the pulse count
can appear at a Pulse Output on another -1 or Digital Output on a -3 unit. The pulse input should be
connected in the same way as a digital input.
2.4.7 Pulse Inputs (-2)
For the -2 module, the four digital inputs (DI 1-4) may be configured as pulse inputs. The first