D9000/D7000 Series Operation & Installation Manual
Page 50
74-07692-000-C 4/97
Problems with the D8125 POPEX Data
Expansion Loops
EMI (Electro-magnetic Interference), excessive
resistance, or intermittent grounds, shorts, or
opens on the data expansion loop can cause
erratic or intermittent functioning of points. Follow
the procedures below to find the source of
problems on the data expansion loop.
EMI
If you suspect EMI may be a problem, see
EMI on
Long Wire Runs in this section.
AC induction on the data expansion loops must
be less than 10 VAC.
Metering the Loops
Before you follow the procedures below to meter
the data expansion loops, check Table 1 (on
page 38) to be sure you used the correct gauge
wire for the length of the data expansion loops.
When you meter the loop, monitor it long enough
to observe an intermittent problem.
To meter the data expansion loop without
POPITs connected to it:
1.
Disconnect the loop from the POPEX
module.
2.
Twist the positive and then the negative
wires together at each POPIT location so that
the positive and negative wires are
continuous to the last POPIT location.
3.
At the last POPIT location twist the end of the
positive wire to the negative wire to form one
continuous loop.
4.
Meter the loop for continuity from the point
where it connected to the POPEX module.
Resistance for the entire loop must be less
than 60 ohm. If there is no continuity, find and
repair the open on the loop.
5.
Still metering for continuity, untwist the
negative and positive wires at the last POPIT
location. If the meter does not show an open
condition, find and repair the short on the
loop.
6.
Twist the positive and negative wires at the
last POPIT location back together.
7.
Meter the loop for continuity to terminal 10
(earth ground). If there is continuity, find and
remove the foreign ground on the loop.
8.
Meter the loop to terminal 10 for AC voltage.
AC induction on data expansion loops must
be less than 1 VAC. Try using shielded cable
to reduce AC induction if the AC voltage
exceeds 1 VAC.
Checking Shielded Cable
If improperly installed, shielded cable can create
problems rather than solve them. Follow the
procedure below to check shielded cable for
proper installation.
1.
Remove the drain wire for the shield from
terminal 10.
2.
Meter the drain wire for continuity to terminal
10 (earth ground). If there is continuity, find
and remove the foreign ground on the drain
wire.
3.
Reconnect the drain wire to terminal 10.
4.
Meter the shield at the far end of the cable
(last POPIT location on data expansion
loops) for continuity to a ground reference. If
there is no continuity, find and repair the
open in the shield. Solder and tape all
connections.
EMI on Long Wire Runs
EMI (ElectroMagnetic Interference) can cause
problems on long wire runs for serial devices
(Command Centers, POPITs, etc.). The use of
shielded cable reduces the effect of this
interference. Some potential sources of noise on
a long wire run include:
•
Radio or television transmitter site.
•
Ham radio operator’s transmitter site.
•
Computer network system.
•
Heavy machinery (large electrical motors).
•
PBX telephone system.
•
High voltage electrical equipment or
transformers (arc welders, certain medical
and dental equipment, etc.).
•
Public service office using radio
communications (fire department, police
department, etc.).
•
Close proximity to electrical lines, telephone
cabling, or fluorescent lighting fixtures.
There are many other possible sources of noise.
If you suspect that noise may be a problem, the
use of shielded wire is strongly recommended.
Connect the drain wire from the shielded cable to
terminal 10 on the panel.
The drain wire must have continuity from the
panel to the last serial device on the wire run. If
you cut the cable to install devices between the
last device and the panel, be certain to reconnect
the drain wire to insure continuity to the last serial
device.
If continuity is not maintained between the panel
and the last serial device, the shielded cable may
aggravate potential noise problems rather than
eliminate them. Connecting the drain wire to
ground at other than terminal 10 on the panel
may also produce problems. Do not connect the
drain wire to any other ground source.
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