Bird Technologies 8251D208 - Manual (Page 25)

3. Replace vent plug. If coolant needs to be added,
refer to the RF Load Resistor section.
DC Resistance Measurement
Preparation
and Tools
Required
Be sure that the vent plug is installed.
Preparation:
s Tools: Common hand tools
s Ohmmeter with an accuracy of ± 1% at 50
ohms.
s Temperature of the load between 20°C to 25°C
(68°F to 77°F)
Accurate measurement of the dc resistance between the in-
ner and outer conductors of the RF input connector will pro-
vide a good check of the condition of the load resistor.
Checking the dc resistance is simply used to measure a
change in the condition of the resistor over time. The track-
ing of the dc resistance must start before the resistor is first
put into service. Perform the following steps and record the
value for future comparison. Check and record the resis-
tance of the load periodically according to use.
WARNING
Never attempt to connect or disconnect RF equipment
from the transmission line while RF power is being
applied. Leaking RF energy is a potential health
hazard.
Checking the
DC Resistance
Measure the dc resistance. Follow the instructions below.
1. Turn off RF power and interlock circuitry before
any electrical disconnection’s are made.
2. Disconnect the RF coaxial line.
3. Connect the multimeter test leads across the cen-
ter and outer conductor of the load resistor. Refer
to figure 4 for placement of the leads.
4. Record the value of the resistance before the load
is put into service. Compare subsequent values
with the latest reading. If the values vary more
than 2 ohms this could be an indication of a fail-
ing resistive element.
13
Maintenance