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The meter comprised a moving coil meter, voltage and precision resistors, and switches and sockets to select the range. The first Avometer had a sensitivity of 60 Ω/V, three direct current ranges (12 mA, 1.2 A, and 12 A), three direct voltage ranges (12, 120, and 600 V or optionally 1,200 V), and a 10,000 Ω resistance range. An improved ...
A moving coil meter has a different and equally distinctive structure. A horseshoe magnet with a keeper in use A magnet keeper is a specialised pole piece used to temporarily connect the poles of a permanent magnet, to help to preserve the magnetism, and for safety in the case of large and powerful magnets.
A useful meter generally contains a provision for damping the mechanical resonance of the moving coil and pointer, so that the pointer settles quickly to its position without oscillation. The basic sensitivity of a meter might be, for instance, 100 microamperes full scale (with a voltage drop of, say, 50 millivolts at full current).
This moving coil galvanometer is mainly used to measure very feeble or low currents of order 10 −9 A. To linearise the magnetic field across the coil throughout the galvanometer's range of movement, the d'Arsonval design of a soft iron cylinder is placed inside the coil without touching it. This gives a consistent radial field, rather than a ...
Diagram of D'Arsonval/Weston type galvanometer. As the current flows from + terminal of the coil to − terminal, a magnetic field is generated in the coil.This field is counteracted by the permanent magnet and forces the coil to twist, moving the pointer, in relation to the field's strength caused by the flow of current.
The moving iron ammeter symbol is in the lower-left corner of the meter face. Moving iron ammeters use a piece of iron which moves when acted upon by the electromagnetic force of a fixed coil of wire. The moving-iron meter was invented by Austrian engineer Friedrich Drexler in 1884. [5]
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The first Avometer was made by the Automatic Coil Winder and Electrical Equipment Co. in 1923, and measured direct voltage, direct current and resistance. [1] 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.