Measuring instruments
Se denominan instrumentos de mediciones eléctricas a todos los dispositivos que se utilizan para medir las magnitudes eléctricas y asegurar así el buen funcionamiento de las instalaciones y máquinas eléctricas. La mayoría son aparatos portátiles de mano y se utilizan para el montaje; hay otros instrumentos que son conversores de medida y otros métodos de ayuda a la medición, el análisis y la revisión. La obtención de datos cobra cada vez más importancia en el ámbito industrial, profesional y privado. Se demandan, sobre todo, instrumentos de medida prácticos, que operen de un modo rápido y preciso y que ofrezcan resultados durante la medición.
Existen muchos tipos de instrumentos diferentes siendo los más destacados los amperímetros, voltímetros, óhmetros, multímetros y osciloscopios.
Galvanometer
Galvanometers are devices used to indicate the passage of electric current through a circuit and to accurately measure its intensity. They are usually based on the magnetic or thermal effects caused by the passage of current.
In a moving magnet galvanometer, the indicator needle is associated with a magnet that is located inside a coil through which the current that we are trying to measure circulates and that creates a magnetic field that, depending on its direction, produces an attraction or repulsion of the magnet proportional to the intensity of said current.
In the case of thermal galvanometers, what is revealed is the elongation produced when a very fine thread wound around a cylinder integral with the indicator needle is heated, due to the Joule Effect, as the current passes.
Ammeters
An ammeter is an instrument that is used to measure the intensity of current that is flowing through an electrical circuit.[2] In their original design, ammeters are essentially made up of a galvanometer whose scale has been graduated in amperes. Currently, ammeters use an analog/digital converter to measure the voltage drop over a resistor through which the current to be measured flows. The converter reading is read by a microprocessor that performs the calculations to present the value of the circulating current on a numerical display.
To measure the intensity of the circulating current, the ammeter must be placed in series, so that said current passes through it.
Special care must be taken when using an analog ammeter when making a current measurement. For the terminal where the magnitude to be measured is indicated (in this case A or mA), it must be connected to the part of the circuit where "enter the current to be measured", and the COM terminal must be connected to the remaining part of the circuit that was interrupted to measure the current. If the measurement is not carried out in this way, the needle will deflect in the opposite direction to that established by the instrument, causing possible breakage of the needle.
This means that the ammeter must have as small an internal resistance as possible, so that it does not produce an appreciable voltage drop. To do this, in the case of instruments based on the electromagnetic effects of electric current, they are equipped with coils of thick wire with few turns.
Voltmeters
A voltmeter is an instrument that is used to measure the difference in potential or voltage between two points of an electrical circuit that is closed but at the same time open at the poles. Voltmeters are classified by their mechanical operation, being in all cases the same instrument:.
To measure the potential difference, the voltmeter must be placed in parallel, that is, in derivation on the points between which the measurement is to be carried out. To this end, in the case of instruments based on the electromagnetic effects of electric current, they are equipped with coils of very fine wire with many turns, so that with a low intensity of current through the device the necessary force is achieved to move the indicator needle.[3].
Ohmmeter
An ohmmeter or ohmmeter is an instrument for measuring electrical resistance. The design of an ohmmeter consists of a small battery to apply a voltage to the resistance under measurement, and then using a galvanometer to measure the current that circulates through the resistance. The scale of the galvanometer is calibrated directly in ohms, since in application of Ohm's law, since the battery voltage is fixed, the current circulating through the galvanometer will only depend on the value of the resistance under measurement, that is, the lower the resistance, the greater the current intensity and vice versa.
There are also other types of more accurate and sophisticated ohmmeters, in which the battery has been replaced by a circuit that generates a current of constant intensity I, which is circulated through the resistance R under test. A precision ohmmeter has four terminals, called Kelvin contacts. Two terminals carry the constant current from the meter to the resistance, while the other two allow the measurement of the voltage directly between its terminals, so the voltage drop in the conductors that apply said constant current to the resistance under test does not affect the accuracy of the measurement.
Polymeter
A multimeter, also called a multimeter or tester, is an instrument that offers the possibility of measuring different magnitudes in the same device. The most common are the voltmeter, ammeter and ohmmeter. It is frequently used by technical personnel in the entire range of electronics and electricity. There are different models that incorporate, in addition to the three basic functions mentioned above, other important measurements, such as measurement of inductances and capacitances; diode and transistor tester; or scales and sockets for temperature measurement using standardized thermocouples.
There are also multimeters with advanced functions and measure current that allow: generating and detecting the intermediate frequency of a device, as well as an amplifier circuit with a speaker to help tune the circuits of these devices; tracking the signal through all stages of the receiver under test; perform the oscilloscope function above one million samples per second in scanning speed, and very high resolution; synchronize with other measuring instruments, including other multimeters, to make point power measurements (power = voltage * intensity); be used as a telephone device, to be able to connect to a telephone line under test, while measurements are carried out on it or on an adjacent one; Perform automotive electronics circuit checks and record high or low voltage bursts.
This measuring instrument, due to its price and accuracy, continues to be the favorite of the amateur or professional in electricity and electronics. There are two types of multimeters: analog and digital.
Oscilloscope
An electronic measuring instrument is called an oscilloscope for the graphic representation of electrical signals that can vary over time, which allows the visualization of transient phenomena as well as waveforms in electrical and electronic circuits and through its analysis it is possible to easily diagnose the problems in the operation of a certain circuit. It is one of the most versatile electrical measurement and verification instruments that exist and is used in a large number of technical applications. An oscilloscope can measure a large number of phenomena, if it is equipped with the appropriate transducer.
The oscilloscope presents the values of electrical signals as key points on a screen, with the X (horizontal) axis typically representing times and the Y (vertical) axis representing voltages. The image obtained in this way is called an oscillogram"). They usually include another input, called the "Z axis" that controls the luminosity of the beam, allowing some segments of the trace to be highlighted or turned off. The operation of the oscilloscope is based on the possibility of deflecting a beam of electrons by creating electric and magnetic fields. The dimensions of the CRT screen are currently standardized in most instruments, at 10 cm on the horizontal axis (X) by 8 cm on the vertical axis (Y).
The oscilloscope is manufactured in many different forms, not only in terms of the purely physical aspect but also in terms of its internal characteristics and therefore its performance and application possibilities. There are two types of oscilloscopes: analog and digital. Analog ones work with continuous variables while digital ones work with discrete variables. Both types have their advantages and disadvantages. Analog is preferable when it is a priority to visualize rapid variations of the input signal in real time. Digital oscilloscopes are used when you want to view and study non-repetitive events, such as voltage that occurs randomly.
Spectrum analyzer
A spectrum analyzer is an electronic measurement device that allows the spectral components of the signals present at the input to be displayed on a screen. These can come from any type of electrical, mechanical, acoustic, optical or electromagnetic waves, but they must be converted to electrical waves with the respective transducer. Electromagnetic waves, for example, are captured with an antenna that will be connected to one of the 50 ohm input connectors, generally BNC.
On the ordinate axis, the level in dB of the spectral content of the signal is usually presented on a logarithmic scale. The frequency is represented on the x-axis, on a scale that is a function of the temporal separation and the number of samples captured. The center frequency of the analyzer is the frequency that corresponds to the frequency at the midpoint of the screen. The spectrum of electrical power is often measured with them.[4].
It is currently being replaced by the vector signal analyzer.
Energy monitors
They are real-time meters of different electrical parameters. They allow instantaneous reading of quantities such as current intensity per phase, phase voltages and line voltages, different values of electrical powers, power factor, frequency, etc.
They are instruments for comprehensive electrical measurements that help control the electricity consumption of each device. Designed so that electrical parameters can be easily known, facilitating fault detection and optimizing electrical consumption.
They have a PC interface for data disclosure through specific software. Some of the models can adapt to remote systems such as SCADA.