Bird Electronic Econoload 8730 Series, Инструкция

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3
Chapter 2 Theory Of Operation
Resistor
Bird 8730 Series Econoloads consist of a thin-film-on-ceramic resistor
immersed in externally-supplied coolant. The coolant flows directly
over the resistor instead of using an intermediate heat transfer
system, reducing the load size to a minimum. After passing over the
entire length of the resistor, the coolant leaves the load and can
either be discarded or cooled in a heat exchanger and reused.
Coolant
The load’s electrical and thermal performance is reduced by
impurities or chemical additives in the coolant, especially ones which
are deposited as scale on the resistor. This may cause the load to
overheat and fail. Salt water will have a similar effect and should not
be used. For recommended coolant, refer to “Coolant” on page 6 and to
“Specifications” on page 21.
Optional
Flow Interlock
A minimum coolant flow of four galons per minute is required at all
times to dissipate the heat from RF power. When the flow rate drops
below this point, the flow switch opens causing immediate
transmitter shutdown. The flow switch is a “normally open” type, and
is closed during normal operation.
After flow is restored, a time delay switch keeps the interlock open for
an additional 12 seconds. This ensures proper operation of the cooling
system before applying RF power, preventing resistor burnout.
Optional Thermal
Interlock
(8732A Only)
The 8732A can be supplied with an optional passive overtemperature
thermoswitch. Normally closed, it opens at a preset temperature,
turning off transmitter power. The temperature setting is preset at
the factor for either 72 or 79 °C (162 or 175 °F). The interlock system
will not permit use of the transmitter until the load has reached a
safe temperature.