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The first electric devices
The development of research in the field of electrical and magnetic phenomena and enhance their practical applications have necessitated the development of methods for measuring basic electrical quantities, and the creation of special electrical devices.
The principle of operation of the first electric appliances was based on the deviation of the magnetic needle by an electric current. However, such devices are essentially the only indicators of current.
The first indicator of electrical current multiplier was I. X. Shveyggera created in 1820 m. It is a framework that consists of a few turns of wire, which was placed inside a magnetic needle. Experiments have shown that an increase in the number of turns of the coil amplifies the effect of the current on the arrow. However, due to the influence of terrestrial magnetism on the magnetic needle of the multiplier his testimony was inaccurate.
In 1821 was found (Ampere), the possibility of eliminating the influence of terrestrial magnetism using an astatic pair consisting of two magnetic needles, fortified on a common axis and parallel to one another, and the arrow poles facing in opposite directions.
In 1825, Italian physicist L. Nobili astatic couple has combined with the multiplier and made more sensitive device. For practical measurements were necessary instruments with direct-reading, pre-calibrate, for which it would be possible to count the measured values.
The first devices to measure the amount of current
It is clear that the greatest need first arose in the direct measurement of the value of the current flowing through the conductor. The first step in this direction was the creation of switch devices in which the sine or tangent of the deflection angle of the arrow was proportional to the current. Such devices are called the sine galvanometer and the tangent-galvanometer.
In 30-ies of XIX century. widely spread-tangent galvanometer Helsingfors University professor I. Nervandera. However, direct determination of the measured value with the help of such a device has been difficult. It was necessary to calibrate the device.
The first attempt to calibrate the galvanometer was made in 1839 BS Jacobi. By including the galvanometer in series in a single chain with voltameter, Jacobi was able to establish a relationship between the amount of current is determined by means of electrolysis, and the deviation of the magnetic needle of the galvanometer. Thus, it was established the concept of graded by the amount of current the galvanometer and introduced the method of grading, widely spread.
Of great importance for the development of electrical instrument was the creation of an electromagnet (1825, William Sturgeon). Since the second quarter of XIX century., Electromagnets have been widely used in various electrical appliances and devices.
New methods for electrical and magnetic measurements
The presence at the disposal of physics and electrical engineering devices and components such as solenoid, relay, astatic couple SLR range, springs to create a counter-torque, allowed to go to the construction of more sophisticated electrical devices. Already in the first half of XIX century. are more sensitive and accurate galvanometer elektrodinamometr static galvanometer and so on. n.
Advances in the field of theoretical and experimental studies led to the discovery of new methods for electrical and magnetic measurements. These include the development of ballistic measurement method (E. X. Lenz, 1832), the compensation method (I. Poggendorff, 1841), a bridge measuring circuit (Charles Wheatstone, 1843), and others.
Ballistic method based on measuring in a ballistic galvanometer number of pulses of electricity induced by a change in flux linkage of the coil windings included in the chain of the galvanometer.
Ballistic galvanometer different from the usual mirror galvanometer much greater moment of inertia of the moving part of the device that allows the movement of its frame after the cessation of current in it. Fundamentals of ballistic galvanometer theory developed by Lenz.
The action of the induced current was considered as an instant hit (hence the name of the device: the ancient Greek ballista-throwing weapon), under whose influence multiplier arrow deflected at a certain rate, and this rate is proportional to sin a / 2, where a - angle of greatest deflection of the arrow.
Compensation measurement method greatly improves the measurement accuracy. The main advantage of this method is that the measurement is made at the full compensation of the currents in the individual branches, when the light through the current does not pass (zero display). This excludes the error caused by the voltage drop in the wires, the measurement of the inevitable ordinary voltmeter.
Compensation method is widely used in low-power circuits, where the switch is connected with the measuring devices power consumption commensurate with the power consumed in the circuit being measured.
Electrical appliances for measuring resistance
The development of telegraphy and several other electrical applications demanded a device for measuring the resistance. In the 40-60-ies developed the first design resistors ( "voltagometr" BS Jacobi), rheochords (I. Poggendorff), Shops of resistance, and other similar devices.
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