Digital Multi meter DT-830D
A Digital Multi meter DT-830b, also known as a VOM (volt-ohm-milliammeter), is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter can measure voltage, current, and resistance. Analog multimeters use a microammeter with a moving pointer to display readings.
Digital Multi meter DT-830b 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.
A Digital Multi meter DT-830b can be a hand-held device useful for basic fault finding and field service work, or a bench instrument which can measure to a very high degree of accuracy. Digital Multi meter DT-830b’s are available in a wide range of features and prices. Cheap Digital Multi meter DT-830b’s can cost less than US$10, while laboratory-grade models with certified calibration can cost more than US$5,000.
The first moving-pointer current-detecting device was the galvanometer in 1820. 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. These galvanometers were bulky and delicate.
The D’Arsonval–Weston meter movement uses a moving coil which carries a pointer and rotates on pivots or a taut band ligament. 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.
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 instrument’s scale, which made measurement quick and easy.
The basic moving coil meter is suitable only for direct current measurements, usually in the range of 10 μA to 100 mA. 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.
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.
Multimeters were invented in the early 1920s as radio receivers and other vacuum tube electronic devices became more common. 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.
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. 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.
The Digital Multi meter DT-830b is a very affordable and handy piece of test equipment. It features an easy to read 3.5 digit LCD display. It is equipped with 5 functions and 19 ranges, each test position is quickly and easily selected with a simple turn of the single selector switch.
It also has a built-in diode test and transistor test feature. There is a buzzer for continuity test. This meter has a replaceable 0.2A/250V fuse accessible via the battery compartment.
- Measure DC voltage in these ranges: 200 mV 2000mV, 20V, 200V and 1000V.
- Measure DC current in these ranges: 200µA, 2000µA, 20ma, 200ma and 10A.
- Measure AC voltage in these ranges: 200 V and 750 V.
- Measure resistance in these ranges: 200, 2000 ohms, 20, 200 and 2000K ohms.
- Transistor Hfe Measurement
- Continuity Tester with Buzzer
- Removable Test Leads Included
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