Radio/Serial Telemetry Module
User Manual
Page
20
©
March 2000
Externally powered loops may be connected by connecting the input between "AI 1+" and “AI 1-”
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 905 module is also recommended.
2.4.5
Analogue Outputs (905-1 and 905-3)
The 905-1 module provides two 4 - 20 mA DC analogue outputs for connecting to instrument
indicators for the display of remote analogue measurements. The 905-3 module provides eight 0 -
20 mA DC analogue outputs. Each analogue output is a "sink" to common.
+
-
A 24VDC supply is available on the 905 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 905 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 (905-1)
For the 905-1 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 905-1 or Digital Output on a 905-3 unit. The
pulse input should be connected in the same way as a digital input.
2.4.7
Pulse Inputs (905-2)
