Chapter Two Installation
man_905-105_2.16 Page 19
Digital outputs may be configured to individually turn off if no command message is received to that
output for a certain period. This feature provides an intelligent watch dog for each output, so that a
communications failure at a transmitting site causes the output to revert to a known state. See section
4.4 Changing User Options for further details.
The output circuit is connected to the appropriate pair of "DO" terminals. Each digital output circuit
includes a LED indicator which is lit when the digital output is active.
2.4.3 Digital Outputs (905-2, 905-3 and 905-4)
The digital outputs on the “-2”, “-3” and “-4” modules are transistor switched DC signals, FET output
to common rated at 30VDC 500 mA. The ”-2” provides one digital output; the ”-3” provides eight
digital outputs and the ”-4” provides 4 – 16 outputs. The first four DO’s on the ”-3” and ”-4” modules
are also the pulse outputs - that is, the first four DO's can be either digital outputs or pulse outputs.
The function of each of these outputs may be configured individually. For a description of pulse
outputs, refer to Section 2.4.7.
Digital outputs may be configured to individually turn off if no command message is received to that
output for a certain period. This feature provides an intelligent watch dog for each output, so that a
communications failure at a transmitting site causes the output to revert to a known state. See Chapter
4 Configuration for further details.
The output circuit is connected to the appropriate pair of "DO" terminals. Each digital output circuit
includes a LED indicator which is lit when the digital output is active.
2.4.4 Analog Inputs (905-1 and 905-2)
The ”-1” module provides two 4 - 20 mA DC analog inputs for connecting to instrument transducers
such as level, moisture, pressure transducers, etc. The ”-2” module provides six 0 - 20 mA DC analog
inputs. Note that the inputs on the ”-2” module will measure down to 0mA, so they can also be used
for zero based signals such as 0 - 10 mA. The modules transmit the “mA value” of the input, not a “%
of range”, so the output value is set to the correct mA signal.
Each analog input has a positive and negative terminal, and may be placed at any point in the current
loop, as long as neither input rises above the 24 volt 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,
however additional protection may be required in high voltage or noisy environments or for very long
wiring runs.
A 24VDC loop supply is available on the module for powering the analog transducer loops. In this
case, the analog loop should be connected between a "AI 1-" terminal and "COM" ( for the first analog
input) or "AI 2-" ( for the second analog input), and so on for other inputs.
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