Electrical measuring instruments are widely used in teaching laboratories. These devices are used to obtain values of various magnitudes that are involved in an electrical circuit. With the appropriate devices we can make measurements of electrical current, voltage and electrical resistance.
The measurement of electric current
A device capable of indicating the presence of electrical current in an electrical circuit is called a galvanometer. If it is possible to graduate the scale of this device, it will receive the name of ammeter, which makes it possible to measure the intensity of the electric current. There are both digital and analog ammeters, both are widely used, however the digital allows greater precision in the results.
Analog ammeter
To measure current in an electrical circuit, the ammeter must be connected in series with the circuit. However, this device has an electrical resistance inside, the value of which must be added to the circuit resistance when performing the calculations. In order to make the ammeter's resistance negligible, this device is built with the lowest possible internal resistance.
The voltage measurement
The voltage measurement is better known as the potential difference measurement. To measure the voltage, we use devices called voltmeters. As with the ammeter, there are also analog and digital voltmeters. Both are widely used, but the digital voltmeter allows a better reading of the ddp value as well as the certainty of what is being measured.
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Analog Voltmeter
To measure the ddp between the ends of a resistor, for example, the voltmeter must be connected in parallel with the resistance. This device, like the ammeter, also has an internal resistance. Thus, it is desirable that the current that is diverted to the voltmeter is as small as possible, so that when introducing the voltmeter, the disturbance caused is negligible. Therefore, voltmeters are built with the highest possible internal resistance.
The measure of resistance
To measure the value of a resistance, a device called an ohmmeter is used, however, if we have a multimeter, a device that has ability to measure values of voltage, electrical current and also resistor resistance, we can measure the resistance value of a resistor. To perform this measurement, simply connect the multimeter's tips to the resistor terminals.
multimeter
By Marco Aurélio da Silva
Brazil School Team
Electricity - Physics - Brazil School
Would you like to reference this text in a school or academic work? Look:
SANTOS, Marco Aurélio da Silva. "What are electrical measuring instruments?"; Brazil School. Available in: https://brasilescola.uol.com.br/fisica/quais-sao-os-instrumentos-eletricos-medida.htm. Accessed on June 27, 2021.
