An improved version of 1927 increased this to 13 ranges and 166.6 Ω/V (6 mA) movement. 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. For meters that do have internal amplifiers (VTVMs, FETVMs, etc.), the input impedance is fixed by the amplifier circuit. 20,000 Ω/V is the best (highest) sensitivity available for typical analog multimeters that lack internal amplifiers.
#Fluke multimeters full
For example, if the meter is set to a range of 300 V full scale, the meter's impedance will be 6 MΩ. "Per volt" refers to the fact that the impedance the meter presents to the circuit under test will be 20,000 Ω multiplied by the full-scale voltage to which the meter is set. Thus a meter with a 50 μA movement will have a "sensitivity" of 20,000 Ω/V. The ohms per volt figure is often called the "sensitivity" of the instrument. The full-scale deflection current may also be expressed in terms of "ohms per volt" (Ω/V). This may load a high-impedance circuit so much as to affect the circuit, thereby giving a low reading. For example, a multimeter using a moving coil movement with full-scale deflection current of 50 microamps (μA), the highest sensitivity commonly available, must draw at least 50 μA from the circuit under test for the meter to reach the top end of its scale. General properties of multimeters Īny meter will load the circuit under test to some extent. The first AVO was put on sale in 1923, and many of its features remained almost unaltered through to the last Model 8. MacAdie, joined ACWEECO in 1927 and became Technical Director. Although a shareholder of ACWEECO, Mr MacAdie continued to work for the Post Office until his retirement in 1933.
The Automatic Coil Winder and Electrical Equipment Company (ACWEECO), founded in 1923, was set up to manufacture the Avometer and a coil winding machine also designed and patented by MacAdie. The meter comprised a moving coil meter, voltage and precision resistors, and switches and sockets to select the range. Macadie invented an instrument which could measure amperes (amps), volts and ohms, so the multifunctional meter was then named Avometer. The invention of the first multimeter is attributed to British Post Office engineer, Donald Macadie, who became dissatisfied with the need to carry many separate instruments required for maintenance of telecommunications circuits. The first attested usage of the word "multimeter" listed by the Oxford English Dictionary is from 1907.
One of the earliest suitable rectifiers was the copper oxide rectifier developed and manufactured by Union Switch & Signal Company, Swissvale, Pennsylvania, later part of Westinghouse Brake and Signal Company, from 1927. To read alternating currents or voltages, a rectifier is needed.
#Fluke multimeters series
It is easily adapted to read heavier currents by using shunts (resistances in parallel with the basic movement) or to read voltage using series resistances known as multipliers. The basic moving coil meter is suitable only for direct current measurements, usually in the range of 10 μA to 100 mA. Instead of balancing a bridge, values could be directly read off the instrument's scale, which made measurement quick and easy. It gives proportional measurement rather than just detection, and deflection is independent of the orientation of the meter. The coil rotates in a permanent magnetic field and is restrained by fine spiral springs which also serve to carry current into the moving coil. The D'Arsonval–Weston meter movement uses a moving coil which carries a pointer and rotates on pivots or a taut band ligament. These galvanometers were bulky and delicate. While useful in the lab, the devices were very slow and impractical in the field. These were used to measure resistance and voltage by using a Wheatstone bridge, and comparing the unknown quantity to a reference voltage or resistance. The first moving-pointer current-detecting device was the galvanometer in 1820.
0 kommentar(er)
