Testing equipment can be put to good use ensuring that electrical equipment is properly installed and safe to operate.Faulty installations can be lethal; the condition of electrical installations can be established when contractors use test equipment.
Analog Multimeter User Instructions Full Feature LineCalterm is please to offer an innovative full feature line of test equipment designed to make electrical work faster and safer. Legal Notice: all of the information and data on this site is for informational purposes only and is provided for the convenience of the user. Some information and data on may contain errors or inaccuracies, or there may be omissions, due to human error, technology issues or otherwise. In addition, the information and data on this site may change at any time. Per volt refers to the fact that the impedance the meter presents to the circuit under test will be 20,000 multiplied by the full-scale voltage to which the meter is set. Please help improve this article by adding citations to reliable sources. Find sources: Multimeter news newspapers books scholar JSTOR ( July 2014 ) ( Learn how and when to remove this template message ). A typical multimeter can measure voltage, current, and resistance. Analog multimeters use a microammeter with a moving pointer to display readings. Digital multimeters ( DMM, DVOM ) have a numeric display, and may also show a graphical bar representing the measured value. Digital multimeters have rendered analog multimeters obsolete, because they are now lower cost, higher precision, and more physically robust. Multimeters are available in a wide range of features and prices. Cheap multimeters can cost less than US 10, while laboratory-grade models with certified calibration can cost more than US 5,000. These were used to measure resistance and voltage by using a Wheatstone bridge, and comparing the unknown quantity to a reference voltage or resistance. While useful in the lab, the devices were very slow and impractical in the field. It gives proportional measurement rather than just detection, and deflection is independent of the orientation of the meter. Instead of balancing a bridge, values could be directly read off the instruments scale, which made measurement quick and easy. Analog Multimeter User Instructions Series Resistances KnownIt 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. To read alternating currents or voltages, a rectifier is needed. 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. 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. Macadie invented an instrument which could measure amperes (amps), volts and ohms, so the multifunctional meter was then named Avometer. The meter comprised a moving coil meter, voltage and precision resistors, and switches and sockets to select the range. Although a shareholder of ACWEECO, Mr MacAdie continued to work for the Post Office until his retirement in 1933. His son, Hugh S. MacAdie, joined ACWEECO in 1927 and became Technical Director. The first AVO was put on sale in 1923, and many of its features remained almost unaltered through to the last Model 8. For example, a multimeter using a moving coil movement with full-scale deflection current of 50 microamps (A), the highest sensitivity commonly available, must draw at least 50 A from the circuit under test for the meter to reach the top end of its scale. This may load a high-impedance circuit so much as to affect the circuit, thereby giving a low reading. The full-scale deflection current may also be expressed in terms of ohms per volt (V). The ohms per volt figure is often called the sensitivity of the instrument. Thus a meter with a 50 A movement will have a sensitivity of 20,000 V.
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