User's Manual

Hardware and Wiring Installation Guide 21
The collector network (2-pair) must be tested before the system power is applied to be sure that wires
are not misconnected. Failure to thoroughly test the collector network wiring may result in equipment
damage.
The concentrator and collector devices connect to the 2-pair wiring system using modular interfaces to
allow for easy testing of the wiring before power is applied. It is recommended that installers be
equipped with appropriate USOC cable testers as required to verify the polarity and validity of
installed wiring.
Note that 3-pair USOC interconnections may also be used. In this case, the third pair (outermost) is
used in parallel with the second pair to improve power distribution to the collectors.
4.5.2 Setting the "Last Unit" Switch on a Collector
When installing collectors, the collector network wires run from unit to unit in a daisy chain fashion.
Each collector has a small switch for identifying the last collector on a line. It is very important that the
collectors which are NOT at the end of the line have this switch set to the UNTERMINATED position,
and that the collector which is at the end of the line has this switch set to the TERMINATED position.
Terminated Unterminated
The reason for this is that with high speed digital data, it is critical that the electrical energy that runs
down the wires is absorbed at the end and does not "bounce back" down the wire and cause
interference with other data coming down. To exactly absorb all the energy coming down a wire, the
wire must be ended at the last device in the chain with a resistor, which has value that equals the
characteristic impedance of the wire. Each collector unit is equipped with such a resistor that is
connected when the switch is in the TERMINATED position.
4.5.3 Power-up Test
Collectors are provided with a 24V power supply that must always be used for each collector,
providing local operating power. No other power supply is adequate to power collectors. To ensure
that the power supplies do not pull out by their own weight, either mount the power strip outlet side up
or use wire ties to hold the power supply in place.
When the collector wiring and isolation have been verified and the cable connection between the
concentrator and the collector has been tested and found correct, the next step is to apply power to the
collector and check the sensor connections for the correct voltages.
Power supply may
become
disconnected if
power strip is
mounted sideways.
Use wire ties to hold the
power supply in place.