Molly Ayala
A voltmeter is a device used to measure the voltage or potential difference between two points in an electric circuit. It is connected in parallel with the circuit and usually has a high resistance to take negligible current from the circuit. Voltmeters can be either analog or digital, with the former using a pointer to indicate voltage on a scale and the latter providing a numerical display. They are commonly used to measure voltages in electrical circuits or electronic devices and can be employed in various sectors, including automotive, electrical troubleshooting, and laboratory studies.
Characteristics and Values of Voltmeter
| Characteristics | Values |
|---|---|
| Definition | An instrument used for measuring electric potential difference between two points in an electric circuit. |
| Types | Analog, Digital, PMMC, Electro-dynamometer, Amplified, Vacuum Tube, FET-VM, Handheld, Desktop, Laboratory, Radio Frequency (RF) |
| Measurement | Voltage, Current, Resistance |
| Scale | Volts, Millivolts, Kilovolts |
| Connection | Parallel |
| Power Source | Battery, Measured voltage source |
| Uses | Monitoring generators, Test instruments, Home electronics, Electrical panels, Electric motors, Solar energy systems, Automotive, Laboratory studies, Electrical design |
| Accuracy | Analog - a few percent of full scale, Digital - better than 1%, Specially calibrated test instruments - a few parts per million |
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What You'll Learn
How does a voltmeter work?
A voltmeter is an instrument used to measure the electric potential difference between two points in an electric circuit. It is connected in parallel and has a high resistance, meaning it takes negligible current from the circuit.
The voltmeter provides a path for charges to travel between two points in a circuit, and the work they do on that journey is what is measured as the potential difference or voltage.
There are various types of voltmeters, including digital and analog, and they can be used to measure both direct and alternating electric currents.
Digital Voltmeter
Digital voltmeters (DVM) measure an unknown input voltage by converting the voltage to a digital value and then displaying the voltage in numeric form. This is done using an analog-to-digital converter (ADC). There are multiple ways an ADC can work, such as by charging a capacitor and comparing it to multiple internal reference voltages, or by using an integrator circuit.
Analog Voltmeter
Analog voltmeters move a pointer across a scale in proportion to the voltage measured. They can be built from a galvanometer and series resistor. The galvanometer has a coil of fine wire suspended in a strong magnetic field. When an electric current is applied, the interaction of the magnetic field of the coil and the stationary magnet creates a torque, making the coil rotate. The torque is proportional to the current passing through the coil. The coil rotates, compressing a spring that opposes the rotation.
Other Types of Voltmeter
Voltmeter sensitivity and input resistance can be increased by supplying the current required to deflect the meter pointer with an amplifier and power supply, instead of the circuit under test. This allows for the use of a rugged moving coil instrument with higher input resistance, reducing the current drawn from the circuit under test.
Voltmeter configurations can also be either direct or indirect. While direct voltmeter configurations work well for reading a range of voltages, they may require resistors to be soldered together to produce the exact value. An indirect voltmeter configuration connects one or more series resistances together in a series chain with the meter to give the desired voltage range.
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What are the different types of voltmeters?
A voltmeter is an instrument used to measure the electric potential difference in volts between two points in an electric circuit. It is connected in parallel and has a high resistance, allowing it to draw negligible current from the circuit.
There are several types of voltmeters, including:
Analog Voltmeter
Analog voltmeters move a pointer across a scale in proportion to the voltage measured. They are typically built from a galvanometer and series resistor. While they may not be as accurate as digital voltmeters, they are still widely used and can measure voltages from a fraction of a volt to several thousand volts.
Digital Voltmeter (DVM)
Digital voltmeters provide a numerical display of voltage by using an analog-to-digital converter. They generally have higher accuracy than analog voltmeters and can measure very low voltages of microvolts or less. Digital voltmeters can be designed with different input resistances depending on the voltage range and desired accuracy.
Permanent Magnet Moving Coil (PMMC) Voltmeter
PMMC voltmeters are suitable for measuring DC voltage due to their permanent magnets and constant resistance. They are commonly used in DC voltmeters and offer the advantage of extending the range of voltage measurement.
Moving Iron (MI) Voltmeter
MI voltmeters can measure both AC and DC voltages. They are versatile and can handle voltage polarity reversals without issues.
Electro Dynamometer Type Voltmeter
This type of voltmeter can measure both AC and DC voltages.
Induction Type Voltmeter
Induction voltmeters are not commonly used due to their high cost and inaccuracy in measurements.
Electrostatic Type Voltmeter
These voltmeters use the mutual repulsion between two charged plates to deflect a pointer attached to a spring. They are sensitive to voltages over 100 volts and can work with alternating or direct current.
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How accurate are voltmeters?
A voltmeter is an instrument used for measuring the electric potential difference in volts between different points of an electrical circuit. It is connected in parallel and usually has a high resistance so that it takes negligible current from the circuit.
The accuracy of voltmeters varies depending on their type and the technology used. Analog voltmeters, for example, may have an accuracy of a few per cent of the full scale and are used with voltages ranging from a fraction of a volt to several thousand volts. They work by moving a pointer across a scale in proportion to the voltage measured.
Digital voltmeters (DVMs), on the other hand, generally have higher accuracy, typically better than 1%. They measure voltage by converting it to a digital value and then displaying the result in numeric form. The accuracy of DVMs can be affected by factors such as temperature, input impedance, and power supply voltage variations. Additionally, DVMs with higher input resistance, such as those used in laboratories, tend to be more accurate.
The challenge in ensuring the accuracy of voltmeters lies in their calibration. Calibration involves comparing the voltmeter's readings with a highly precise known voltage reference. In laboratories, the Weston cell, which uses a stable chemical reaction, is commonly used as the standard voltage for precision calibration. This method was widely accepted until 1990 when the definition of the volt changed. Now, the volt is defined using an array of Josephson junctions, and other physical voltage references, such as the Brokaw bandgap reference or a zener diode, are used for calibration.
To maintain accuracy, voltmeters should be periodically calibrated against a voltage standard. This process ensures that the voltmeter's readings fall within the manufacturer's specified tolerances. Additionally, some voltmeters may have built-in calibration adjustments to fine-tune their accuracy.
In summary, the accuracy of voltmeters can vary depending on their type, technology, and calibration. While digital voltmeters generally offer higher accuracy, both analog and digital voltmeters can provide reliable measurements when properly calibrated and used within their specified ranges.
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What are voltmeters used for?
A voltmeter is a device used to measure the voltage or electric potential difference between two points in an electric circuit. It is connected in parallel with the circuit, as this setup ensures that the voltmeter and the circuit experience the same potential difference. Voltmeter measurements are usually taken in volts, millivolts, or kilovolts.
Voltmeter measurements can be displayed in either analogue or digital form. Analogue voltmeters indicate voltage using a needle or pointer on a scale, while digital voltmeters show the voltage value on a numerical screen. Digital voltmeters are generally considered to be more accurate than analogue voltmeters.
Voltmeter applications are diverse, and they are used in both residential and industrial settings. In homes, voltmeters can be used to check the voltage levels of electrical appliances and outlets, ensuring the protection of home electronics. In industrial settings, voltmeters are used to check the voltage of electrical panels, electric motors, and solar panels. They are also used in automotive settings to monitor the status of a vehicle's battery.
Voltmeters are also essential tools in scientific research and electrical design. Electrical engineers and technicians use voltmeters to troubleshoot electrical issues, verify voltage levels, and ensure the proper functioning of circuits.
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How are voltmeters powered?
A voltmeter is an instrument used for measuring the voltage or potential difference between two points of an electronic or electrical circuit. It is connected in parallel and usually has a high resistance so that it takes negligible current from the circuit.
Voltmeter instruments are made in a wide range of styles, with some separately powered (e.g. by battery), and others powered by the measured voltage source itself. Portable voltmeters are usually powered by batteries, while panel-mounted voltmeters are powered by the measured voltage source.
The vacuum tube voltmeter (VTVM) is a once-popular form of voltmeter that was almost always powered by the local AC line current and was, therefore, less portable. Today, these circuits use a solid-state amplifier using field-effect transistors, hence FET-VM, and appear in handheld digital multimeters as well as in bench and laboratory instruments.
Digital voltmeters (DVM) measure an unknown input voltage by converting the voltage to a digital value and then displaying the voltage in numeric form. DVMs are usually designed around a special type of analog-to-digital converter called an integrating converter. The accuracy of a DVM is affected by factors such as temperature, input impedance, and power supply voltage variations.
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Frequently asked questions
A voltmeter is a device used to measure the voltage or potential difference between two points of an electronic or electrical circuit.
There are two main types of voltmeters: analog and digital. Analog voltmeters display the measured voltage using a needle or indicator on a scale. Digital voltmeters display the measured voltage on a numerical screen.
A voltmeter is connected in parallel to a device or circuit to measure the voltage. This setup is important as objects in parallel tend to experience the same potential difference. Voltmeters have a high internal resistance, which impedes the flow of current through it, allowing for correct voltage readings.
Voltmeters are used in various fields, including automotive, electrical troubleshooting, laboratory studies, and electrical design. They are also used to check voltage levels in home electronics, electrical panels, electric motors, and solar energy systems.
