ClassNet Terminal User Manual
14
support a maximum load of 31 ClassNet Terminals plus the Intelligent
RS-485 adaptor per network.
The easiest method of allowing more than 31 ClassNet Terminals is to
split the network into multiple sections, and run each section from its
own Intelligent RS-485 adaptor on different serial ports on a single PC.
Typical PC’s have two serial ports, and multiple serial port expansion
boards are available that provide two, four or eight additional serial ports.
Remember that each section of the network can be up to 1200 metres
long, and can support up to 31 units.
Although we have had some users connect more than 31 ClassNet
Terminals together in a single network without experiencing any
problems, we do not recommend doing so.
Power Requirements
The ClassNet Terminal requires 8 to 16 volts AC or 9 to 18 volts DC at
100mA, which is normally supplied over the CAT5 network cable.
The Intelligent RS-485 Adaptor requires 9 to 18 volts DC at 100mA,
which is normally supplied by a 9v DC 300mA plug pack power supply,
via a centre-positive 2.5mm DC connector.
The Intelligent RS-485 Adaptor can be configured (via an internal
jumper) to supply unregulated DC voltage (from the plug pack powering
the adaptor) to the RS-485 and RS-422 connectors. The maximum
current that can be drawn in this way must be limited to either 500mA, or
100mA less than the capacity of the plug pack, whichever is the smaller.
Note that this output is not fused or protected. We suggest that when
using this capability, the cable length should be restricted to 20 metres.
You should realise that the voltage drop over the network cable can be
very high, especially if the cable run is long, or a large number of units
are being powered. You must ensure that sufficient power reaches each
unit.
In anything other than a very small network, it will usually be necessary
to use more than one power supply, each powering a number of units on
a segment of the cable.
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