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Application Of Devices



Evershed & Vignoles       
Major Megger            
Difficult to tell, these were produced from the 1950s to the 1980s.     
about 8"x4"x4" (200 x 100 x 100mm)               
These instruments are used for testing insulation resistance, mainly in electrical installation work, but also for testing aerial feeders, and the insulation resistance of components (eg transformers and capacitors). This instrument will test with a range of voltages up to 1000V (many insulation testers will only test to 500V). The instrument is self contained, and does not require batteries, power being generated by the crank handle on the side. This instrument was kindly donated by Brian Ormandy.

                                                AVO Meter 

It is often called simply an AVO and derives its name from the first letter of the words amperes, volts, ohms. It was conceived by the Post Office engineer Donald Macadie in 1923.
It was by far the best instrument of its kind in the UK from 1923 to at least the 1960s. Almost uniquely for a radio repairman's multimeter it measures alternating current up to 10 A as well as AC and DC voltages up to at least 1000 V. The Model 8 Mk. V included additional inputs to measure up to 3000 V. As an ohmeter it measures from 0.1 Ω up to 200 kΩ in three ranges. The instrument has an accuracy of ±1% of FSD on DC ranges and ±2% on AC ranges. Its maximum current draw of 50 μA at full-scale deflection (corresponding to 20,000 ohms per volt) is sufficient in most cases to reduce voltage measurement error due to circuit loading by the meter to an acceptable level. A pair of rotary switches are used to select the range to be measured, being arranged in such a way as to minimise the risk of damage to the instrument should the wrong range be selected. Further protection is provided by an overload cut-out and fuses. It was a superb example of British radio engineering in its heyday and was found in many R&D laboratories and virtually every radio repair workshop throughout the country. Even nowadays it can still be found in regular use.

                                                 THE BLACK BOX

The Wright Brothers pioneered the use of a device to record propeller rotations, according to documents provided by L-3 Communications. Since then, the recording medium of black boxes has evolved in order to record much more information about an aircraft's operation.
There are two "black boxes" on modern day aircraft. One is the Cockpit Voice Recorder (CVR) used to record cockpit, intercom, and pilot to controller communications. The other is the Digital Flight Data Recorder (DFDR) used to record aircraft flight control inputs, flight parameters (speed, altitude, etc.), and system performance. The primary use for both is in accident investigation.

Although many of the black boxes in use today use magnetic tape, which was first introduced in the 1960s, airlines are moving to solid-state memory boards, which came along in the 1990s. Magnetic tape works like any taperecorder.  

Black-box manufacturers are no longer making  magnetic  tape recorders as airlines begin a full  transition to solid-state technology.

Solid state uses stacked arrays of memory chips,so they don't have moving parts. With no moving parts, there are fewer maintenance issues and a decreased chance of something breaking duringa crash.

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