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CRT Information Display Systems
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Information Display Systems use CRT’s to display vital information to airplane crew members, and is a rapidly expanding part of the Avionics industry. These display systems typically are either “heads up” or “heads down” and are found in the avionics suites of both military and commercial aircraft. The CRT uses high voltage for the anode element which ranges from 15 to 30 KVDC depending on the size of the tube and whether it is chromatic or mono-chromatic. The high voltage is provided by a power supply integral to the system.
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| The Anode Interconnect System (traditional) |
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| Figure B illustrates the traditional method of interconnecting the CRT anode elements to a high voltage power supply. One end of a .280 diameter silicone rubber cable is connected to the high voltage power supply. The other end is electrically terminated to the CRT anode pin and then potted with a pourable silicone rubber potting material to the the glass envelope of the tube in an attempt to achieve an altitude seal and a moisture barrier. The disadvantages are threefold: (1 ) A failure to the the CRT or the cable itself results in a costly, labor-intensive process to disconnect and re-connect the CRT. (2) The shape and size of the potting at the anode presents a high profile inconsistent with today’s requirement for compactness. (3) The large cable diameter and the relatively large mass of silicone rubber used to effect a moisture and altitude seal makes a reliable seal difficult after numerous hot and cold cycles due to expansion and contraction.
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| The Max Series Solution |
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| Figure A depicts an anode to power supply interconnection using a Max series anode lead assembly that is easy to install, is replaceable and will provide long term reliability. A pre-test of the CRT is possible due to the annular “O” ring on the inner surface of the rubber anode lead cap. Once successful operation is proved, the cup and cap can be pulled off the anode pin and an adhesive applied. When cured, it affords a moisture seal and permits.
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| The Gun End Interconnect System (traditional) |
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| Figure B illustrates the gun or stem end of a CRT and how it is terminated. CRT’s have all the gun end elements exit the tube at the base or stem. Wires are soldered to the tube pins and the entire area, the wires, the tube pins and a portion of the glass stem, are encapsulated. Two of the wires, the focus and the G-2 leads, require high voltage and are connected into the high voltage power supply. This method of construction makes replacement of the CRT a costly procedure since the silicone rubber must be cut away to expose and replace the wires and the entire assembly re-potted. |
| The Avvion Series Interconnect Systems |
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Figure A depicts a gun end interconnect system that does away with the need for encapsulation and allows the user to easily install and replace the major components of an Information Display System. The CRT is replaced by un-threading the Avvion series multi-pin plug coupling ring from the receptacle on the tube gun end. The entire harness can be replaced by un-plugging the Avvion series plug, the Pee-Wee series plug and the low voltage circuit plug.
After installation, the Avvion Interconnect system will operate reliably at the rated voltage at 70,000 feet over a temperature range of -55 to +125° C. Avvion interconnect systems are available for a range of CRT tubes depending on the stem size. The Avvion series of interconnect systems begins on page 56.
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