Flash Technology FTB 312-3, Справочное руководство

Страница: 48 / 78

3-2 Revision13 — 02-20-2001 FTB 312 and FTS 316
RFI Problems
The presence of radio frequency interference
(RFI) can cause a light to flash intermittently, at
the wrong rate, or at the wrong intensity. RFI can
enter the light by any wire to or from the unit. For
example:
•
RFI on primary power wires could cause errors
in flash rate and intensity.
•
RFI on the master/slave interconnecting wire
could cause a light to switch to and remain in
night intensity.
•
RFI on the PEC line could switch a light to
night intensity and force it to remain there.
RFI would not normally cause a light to switch
to day intensity.
•
Strong RFI could burn out circuit board com-
ponents.
While FTCA designed the circuits to reject or
bypass RFI, FTCA cannot guarantee complete
immunity beforehand. After installation, you may
find it necessary to add external filters or use
other methods to reduce RFI entering the equip-
ment.
Component Testing
The following procedures describe how to check
most of the unit’s major electrical components.
Always make resistance measurements with the
primary power turned off. Before applying power
for voltage measurements, connect test leads or
circuit jumpers, or disconnect existing circuit con-
nections, with the power turned off and storage
capacitors discharged.
Wiring and Cabling
Wires or cables that move repeatedly will eventu-
ally break. Ensure that all cables (the flashhead
cable in particular) are securely fastened at short
intervals to the structure or other supports.
Inspection
Closely inspect the units and check the connec-
tions against the installation instructions. Also, a
close inspection may reveal insulation break-
down, an overheated component, corrosion, loose
connections, faulty relays, incorrect hookup, and
so forth.
Power Converter Component Testing
Capacitors
Evaluate the condition of a capacitor with an ana-
log volt-ohmmeter operating in the resistance
mode. The following method assumes an instru-
ment with a X100 resistance scale.
Place the meter leads across the terminals of an
isolated (no electrical connections to other cir-
cuits) and fully discharged capacitor. Observe the
subsequent needle movement.
If the capacitor is functional, the needle initially
indicates zero ohms, but soon begins to rise to
higher indicated values. A capacitor that is dis-
connected from other circuitry is defective if it
does not exhibit this behavior. The length of time
it takes the needle to reach the 1-megohm reading
(about 65% full-scale) is a measure of the capaci-
tance. For example, the time is about 5 seconds
for a 10-mfd. capacitor, or 10 seconds for a 20-mfd.
capacitor, and so forth.
Manually discharge the capacitor before repeat-
ing this measurement. This test may not detect a
malfunction that occurs only at high voltage.
A bank of capacitors connected in parallel may be
checked as a single unit. If the test indicates a
short circuit, the individual capacitors have to be
disconnected and checked separately. A shorted
capacitor is indicated if the resistance does not
rise above zero after several seconds of measure-
ment.
Burst Choke (L1)
The measured resistance of this choke should be
approximately seven ohms.
Relays
A malfunctioning relay may have faulty contacts,
a sticky mechanism, a bad ground, or a defective
coil. You may determine the first two possibilities
by inspection and manually exercising the arma-
ture. You can confirm a defective coil by measur-
ing the resistance. To measure the resistance of
relay coils, first remove the wires from one of the
connections to the coil terminals on the relay.