Voltmeter, what is it and which one to choose?

November 2, 2021

voltmeter is an instrument used to measure the difference in electrical potential between two points in an electrical circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage in the circuit. On the other hand, digital voltmeters offer a numerical display of voltage through the use of an analog-to-digital converter.

Voltmeters are manufactured in a wide range of styles. Instruments permanently mounted on a panel are used to control generators or other stationary devices. Portable instruments, generally equipped to also measure current and resistance in the form of a multimeter, are standard test instruments used in electrical and electronic work.

Any measurement that can be converted to a voltage can be displayed on a meter that is properly calibrated; for example, pressure, temperature, flow or level in a chemical processing plant.

The typical commercial or laboratory standard voltmeter in use today likely employs an electromechanical mechanism in which current flowing through turns of wire is translated into a voltage reading. Other types of voltmeters include electrostatic, which uses electrostatic forces and is therefore the only voltmeter that measures voltage directly rather than by the effect of current.

It is used to measure very low voltages . The electronic voltmeter, which has largely replaced the vacuum tube voltmeter, uses either amplification or rectification. And even both to measure voltages of alternating or direct current. The current required to drive the movement of the meter is not taken from the circuit being measured. Therefore, this type of instrument does not introduce circuit loading errors.

Next, we will talk in more detail about this laboratory instrument, which, along with others such as the Wattmeter or Speedometer, are indispensable in the practice and measurement of numerous experiments. Join us!

What is a Voltmeter?

Voltmeters provide a way to safely measure the voltage, or the difference in electrical potential, between two points in a circuit without changing the voltage in that circuit. The ability to measure voltage is critical to designing and maintaining advanced technology, but it also has more common and practical applications.

For example, let’s say it’s a hot day and you decide to cool off with a fan, but when you plug it in and turn it on, nothing happens. Is the fan broken? Maybe, but the outlet may not be receiving power. A voltmeter could be used to measure the voltage at the outlet, and if it is not around 120 volts, the outlet could break.

Another instance in which a voltmeter could be used is to determine if a battery is charged or depleted. When troubleshooting a car that won’t start, measuring the battery voltage with a voltmeter is a good place to start.

It works on the principle that the torque is generated by the current that it induces due to the measured voltage and this torque deflects the instrument pointer. The deviation of the pointer is directly proportional to the potential difference between the points. The voltmeter is always connected in parallel with the circuit.

It has many practical applications. The voltmeter is used to determine if the battery is charged or not . When a car won’t start, people usually check the battery voltage to determine whether or not this is the problem.

Difference between current and voltage

Voltage is the difference in electrical potential per unit charge, or it can be defined as the energy contained within an electrical circuit. Current is the rate at which electrical charges pass through the circuit.

Some voltmeters are designed to measure direct current (DC), some are specially designed to measure alternating current (AC), and some are designed to measure radio frequency (RF) voltage.

Uses of the Voltmeter

Today, voltage is used in many applications in different magnitudes . Power transmission lines carry electricity at different high voltage levels. In fact, up to hundreds of thousands of volts, which is much higher than the 120 volts in your outlet.

How to use and read the Voltmeter?

It is of utmost importance that the electrical connections in the circuit are correct. Otherwise, the values ​​read by the measuring instruments can often be incorrect. The current rule says: V = I / R (Where C = voltage, I = current, R = resistance).

The voltmeter offers high resistance . If the resistance is low then it will draw a larger current. As such, the circuit under consideration would not receive the proper amount of current. Therefore the voltmeter would give incorrect readings then. Therefore, the voltmeter is designed to have a high resistance. It is always connected in parallel to the circuit.

Voltmeter Construction

The voltmeter is constructed in such a way that its internal resistance always remains high. If it is connected in series with the circuit, it minimizes the current that flows due to the measurement voltage. Therefore disturbing the voltmeter reading.

The voltmeter is always connected in parallel with the circuit so that the same voltage drop occurs across it. The high resistance of the voltmeter is combined with the impedance of the element through which it is connected. And the general impedance of the system is equal to the impedance that the element had. Therefore, there is no obstruction in the circuit due to the voltmeter, and the meter provides the correct reading.

Voltmeter Types

The voltmeter is classified in two ways . Below, we’ll break down their presentations in detail.

Analogical

An analog voltmeter is one that has a scale that moves in proportion to the voltage of the current. Higher the current the higher the scale moves. Any measurement that is convertible to voltage can be measured on a precisely calibrated analog voltmeter.

Examples of such measurements are pressure, temperature, liquid flow, or viscosity. A basic analog voltmeter consists of a galvanometer in series with a high resistance. The combination of galvanometer accuracy and resistance determines the range of voltages that the voltmeter can measure.

One of the design goals of the instrument is to disturb the circuit as little as possible and therefore the instrument must draw a minimum of current to operate. This is achieved by using a sensitive galvanometer in series with a high resistance, and then the whole instrument is connected in parallel with the examined circuit.

A moving coil galvanometer can be used as a voltmeter by inserting a resistor in series with the instrument. The galvanometer has a coil of fine wire suspended in a strong magnetic field. When an electrical current is applied, the interaction of the coil’s magnetic field and the stationary magnet creates a torque, which tends to make the coil rotate.

The torque is proportional to the current through the coil. The coil rotates, compressing a spring that opposes the rotation. The deflection of the coil is therefore proportional to the current, which in turn is proportional to the applied voltage, which is indicated by a pointer on a scale.

Digital

The voltmeter that displays the reading in numerical form is known as a digital voltmeter . The digital voltmeter gives the exact result. The instrument that measures direct current is known as the DC voltmeter, and the AC voltmeter is used in the AC circuit for the measurement of alternating voltage.

A digital voltmeter is one that displays the numerical value of the voltage of the current. Hands-on labs have digital voltmeters ranging from one thousand to three thousand volts. Commercially used voltmeters have multiple ranges, increasing by powers of 10. Like 0-10 volts, 0-100 volts.

Voltmeter Accuracy

General-purpose analog voltmeters can be accurate to a few percent of full scale , and are used with voltages from a fraction of volts to several thousand volts. Digital meters can be made with high precision, generally better than 1%.

Specially calibrated test instruments have higher accuracies, with laboratory instruments capable of accurately measuring to a few parts per million. Meters using amplifiers can measure small voltages of microvolts or less.

Part of the problem with making an accurate voltmeter is that of calibrating it to verify its accuracy. In laboratories, the Weston cell is used as a standard voltage for precision work. Precision voltage references are available based on electronic circuits.

Why do they have high resistance?

The voltmeter is built with a very high internal resistance because it measures the potential difference between the two points in the circuit. The voltmeter does not change the current of the measuring device. If the voltmeter has low resistance, current flows through it and the voltmeter gives the wrong result. The high resistance of the voltmeter does not allow current to pass through it and therefore the correct reading is obtained.

Dr. Loony Davis5
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Born and raised in Brussels in an English family, I have always lived in a multicultural environment. After several work experiences in marketing and communication, I came to Smart Water Magazine, which I describe as the most exciting challenge of my career.
I am a person with great restlessness and curiosity to learn, discover what I do not know, as well as reinvent myself daily, someone who is curious about life and wants to know. I enjoy sharing knowledge.
This is my personal project but I also collaborate in other blogs, it is the case, the most important web on water currently exists in the US, if you are interested you can read my articles here.

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