Bird Technologies 8630B Series - Manual (Page 35)

Maintenance
19
General Maintenance
Measure Load DC
Resistance
Preparation:
y Tools: Common hand tools
y
Ohmmeter with an accuracy of ± 1% at 50 ohms.
y
Temperature of the load between 20°C to 25°C (68°F to 77°F)
Accurate measurement of the DC resistance between the inner and
outer conductors of the RF input connector will provide 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 tracking 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 resistance of the
load periodically according to use.
1. Turn off RF power and interlock circuitry before any electrical
disconnection.s are made.
2. Disconnect RF coaxial line.
3. Connect the multimeter test leads across the center and outer
conductor of the load resistor. Refer to Figure 7.
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
failing resistive element.
Note: It is recommended that this resistance check be performed
each time the load is to be used.
WARNING
Never attempt to connect or disconnect an RF cable while power is
on at the RF power source. Radiated RF energy is a potential health
hazard.
Figure 7
Meter Lead
Placement