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Monday, 22 March 2021

Electrical and Electronic measuring Instruments


Some electrical and electronic measuring instruments are given below.


Ammeters are instruments for measuring electric currents. They have an electromagnet and a permanent magnet, either one of which is movable, although the moving coil type is more uneven. They are not as sensitive as galvanometers due to their design, which causes only a small proportion of the current to flow through the coil. The first one was invented in 1820 by Hans Christian Oersted (Denmark).

Electric Meter

Electric meter is an electrical device which is used to measure the electric current. Electricity Service Provider use watt-hour meters to evaluate in kilowatt-hours the amount of electrical energy consumed by their users. A kilowatt hour has 1000 watt-hours. For example, if Ten, 100 watt light bulbs operated for one hour will consume 1 kilowatt-hour of electricity. The electricity service provider connects the meters to the lines that supplies electricity to households or industries. The staff from electricity service provider reads the meter at regular intervals between one or more months and will give the customer’s bill based on these readings.


Galvanometer is a delicate electrical instrument used mainly to detect and measure small electric currents. Most galvanometers operate on the principle that an electric current flowing through a wire in the presence of a magnetic field produces a force on the wire. A typical galvanometer has a scale with a zero in the centre and numbers at regular intervals on either side. It also has an indicator such as a needle or a beam of light. The indicator remains at zero until a current passes through the galvanometer. A current in one direction causes the indicator move to one side of the zero point. The first galvanometer was invented by Hans Christian Oersted (Denmark) in 1820. The first moving coil type was devised in 1825 by Johann Schweigger (Germany) and in 1828 C.L. Nobilli (Italy) designed an astatic type. A galvanometer with a mirror, making it very sensitive, was invented in 1867 by Lord Kelvin (Scotland).


Oscilloscope is an electronic instrument that displays changing electrical signals. The signals appear as straight or wavy lines or in other patterns on a fluorescent screen. Oscilloscopes are used in such fields as industry, medicine and scientific research. Electronic engineers use the instruments to test computers, radios and other electronic equipment. Doctors use them to study electrical impulses from the brain or heart. Light, mechanical motion and sound can be studied with oscilloscopes. Devices called transducers change these forms of energy into electrical signals. The screen of an oscilloscope is the front of a cathode-ray tube, a special type of vaccum tube. Inside the tube, a device called an electron gun projects a beam of electrons on to the fluorescent screen. A circuit called the time base causes the beam to move repeatedly from left to right. It was invented in 1897 by Karl Ferdinand Braun (Germany).


Potentiometer is a device that measures electric current, voltage and resistance with high precision. It shows voltage differences by comparing an unknown electromotive force with a known one. It is used to calibrate voltmeters or ammeters and as a control element in electronic circuits and devices.


Tachometer is a device that is used for measuring the speed of rotation of a spinning shaft or wheel, usually in terms of revolutions per minute (rpm). Tachometer’s often are used to measue engine rpm in cars, ships and aircraft. Tachometers indicate an engine’s power and its efficiency in converting energy into mechanical force. The drag-type tachometer is widely used in cars. A digital tachometer measures rpm by means of a pulse accompanying each rotation of the crank shaft. An electric tachometer is commonly used in airplanes. Reed tachometers are used on steam turbines and large engines.


Speedometer is an instrument that indicates the speed of a car or other vehicle. The speedometer display may show speed in kilometers per hour, miles per hour or both. There are two types of speedometers: (1) mechanical speedometers and (2) electronic speedometers. A mechanical speedometer indicates speed by means of a dial and a pointer. This type of speedometer is driven by a flexible shaft connected to a set of gears in the vehicle’s transmission. An electronic speedometer consists of a speed-sending unit, a signal conditioner and an electronic digital or analog readout.


The device that increases or decreases the voltage of alternating current can be termed as a transformer. In order to change such voltage, transformers provide a simple, inexpensive way. Electric power companies mainly depend on transformers to transmit alternating current effectively. The circuits such as: home appliances, lights, industrial machinery and other electric equipments ensure proper voltages. Most transformers are made up of two insulated wire coils. One coil, referred to as the primary winding, is attached to the voltage source to be modified. This voltage is the transformer's input voltage. The output voltage is supplied to the desired circuit by the other coil, known as the secondary winding. The primary and secondary windings of most transformers are wrapped around a hollow core made of thin iron or steel sheets. The majority of cores are shaped like a ring or a square. There is no relation between the two coils.


Transistor is a tiny device used in computers, radios, television sets and other electronic equipments. Transistors control the flow of electric current in such equipment. A typical transistor, together with its protective case, is about as large as the eraser on a pencil. Electronic equipment has been revolutionized by transistors. In modern electronic equipment, most transistors are packaged inside devices called integrated circuits. There may be hundreds of thousands of transistors in just one integrated circuit about the size of a postage stamp. Without transistors, companies can’t make pocket calculators or other high-speed computers. Battery worked radios and television would be much larger and highly expensive.


Voltmeter is an instrument that measures the voltage between two points of an electric current. Most commercial voltmeters are galvanometers connected in series with a high resistance. They have scales that read in volts. A typical direct current voltmeter has a magnet shaped like a horse shoe. To each pole of the magnet is attached a semicircular piece of soft iron that also becomes magnetized. These pieces of soft iron direct the magnetic field toward a small iron cylinder placed between the poles of the magnet. Since soft iron becomes highly magnetized, this cylinder concentrates the magnetic field. Voltmeter was invented in 1820 by Hans Christian Oersted (Denmark). The digital style meter was invented in 1952, it uses solid state circuits. Around 1970 integrated circuits were introduced, for use when high accuracy is required.

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