Installation Manual

Versus Technology, Inc.
DT10000-A0001 25 Revision 8 December 1998
8.3 Setting the "Last Unit" Switch
When installing collectors, the collection
network wires are run from unit to unit in a daisy chain
fashion. Each collector has a small switch on it that is
used to identify it as 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.
NOTE:
The last collector in a segment must have the terminate switch set to the Terminate position.
Why? 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.
8.4 Power-up Test
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.
8.5 Sensor Voltage Test
Once power has been applied to the collector, a voltmeter check should be made of the sensors on the punch
block to verify that they are connected correctly. This is done using the voltmeter or multimeter set to a 20-volt
range. Apply the probes to each sensor connection on the punch block and verify that the voltage reading is
approximately 16 volts. If the reading is approximately 20 volts, then there is no sensor connected to this pair or
the wiring to the sensor is open. If the connection is approximately 16 volts, then the sensor is wired correctly
to a single sensor. If the reading is very low or zero, the sensor pair is shorted. (Of course, the 25th pair on the
punch block is unused and will read zero volts.) RF interference may be verified by switching the meter to the
AC scale and reading the voltage. With no tag transmitting over the sensor there should be < 0.1 VAC on a
sensor pair. When all the sensor pairs that have sensors connected are reading correctly, proper sensor
connections are assured.
Terminated Unterminated
Collector
CAUTION:
If the red LED indicator was lit in the concentrator power-up test but does not light now,
remove power from the concentrator quickly and recheck the two-pair wiring. A short
circuit may have occurred in the connection of the collector.
(If this occurs, a safety fuse
internal to the concentrator may be blown.)