Technical Features and Design Changes
– Original AVOmeter designed to measure DC current, DC voltage, and resistance
– Rotary switch for selecting function and range
– Rheostat for controlling current through device under test
– Movement drew 12 mA for full-scale deflection
– Knife edge pointer and anti-parallax mirror
– Additional patents taken out in Czechoslovakia, Austria, France, Germany, and Switzerland
– US patent obtained in 1926
– Redesign of the instrument after three years of production
– New movement with full-scale current of 6 mA
– Introduction of a one-piece phenolic moulding and kidney-shaped window
Universal AVOmeters
– Introduction of Universal AVOmeter in 1931 with both DC and AC voltage current ranges
– All Universal AVOmeters could measure up to 10 A or 12 A (AC)
– Dual sensitivity movement circuit introduced in 1933, doubling the available voltage and current ranges
– Push button switch for selecting higher sensitivity (÷2)
– Model 8 had a push button for reversing the direction of deflection
Measurement Capabilities
– Model 8 Mark II measures from 1 Ω up to 20 MΩ in three ranges
– Accuracy of ±1% of FSD on DC current ranges
– Accuracy of ±2% of FSD on DC voltage ranges
– Accuracy of ±2.25% of FSD on all AC ranges
– Accuracy of ±5% of reading (at center scale only) on resistance ranges
Safety Features and Applications
– Electrical interlock prevents simultaneous selection of AC and DC ranges
– Damping the movement by short-circuiting the moving coil during transit
– Overload cut-out operated by the moving coil frame hitting end stops
– Fuse protection on resistance ranges
– Widely used in British manufacturing, service industry, research and development, education, utilities, and armed forces
Special Purpose Models
– Universal AVOmeter 50-range, later known as Model 7 (1936 to c. 1986)
– AVOmeter Model 8 (Produced from May 1951 to November 2008)
– AVOmeter Model 9
– AVOmeter Model 12 designed for automotive use
– Heavy Duty AVOmeter, originally designed for railway signaling purposes
– AVOminor (1935 to 1952)
– Universal AVOminor (1936 to 1952)
– AVO Multiminor
– Clamp meter, primarily for higher currents
– All current and voltage ranges for the above models are both AC and DC Source: https://en.wikipedia.org/wiki/Avometer
AVOmeter is a British trademark for a line of multimeters and electrical measuring instruments; the brand is now owned by the Megger Group Limited. The first Avometer was made by the Automatic Coil Winder and Electrical Equipment Co. in 1923, and measured direct voltage, direct current and resistance. Possibly the best known multimeter of the range was the Model 8, which was produced in various versions from May 1951 until 2008; the last version was the Mark 7.
The multimeter is often called simply an AVO, because the company logo carries the first letters of 'amps', 'volts' and 'ohms'. The design concept is due to the Post Office engineer Donald Macadie, who at the time of the introduction of the original AVOmeter in 1923 was a senior officer in the Post Office Factories Department in London.
