Bird Technologies 8890-400 Series - Manuale (Pagina 34)

Repairs
As indicated in Disassembly, the element is not subject to
field repair and must be replaced if it is found to be defec-
tive. Similarly if the RF connector in the Series 8890-400 is
damaged it must be replaced.
RF Load Resistor Test
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
(38°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. When the resistor is checked the measured
resistance should be within a range of 49 to 52.5 ohms. Gen-
erally, if the value exceeds this allowance, the load resistor
may need replacement. Perform the following steps and rec-
ord the value for future comparison. Check and record the
resistance of the load periodically according to use.
WARNING
Never attempt to disconnect RF equipment from the
transmission line while RF power is being applied.
Leaking RF energy is a potential health hazard.
1. Turn off RF power and interlock circuitry be-
fore any electrical disconnection’s are made.
2. Disconnect the RF coaxial line.
3. Connect the multimeter test leads across the
center and outer conductor of the load resistor.
Refer to figure 9.
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Bird Model 8890-400 Series Termaline Wattmeter