A voltmeter is an instrument used to measure voltage, or potential difference, between two points. It works on the principle that when a current is induced between two points due to the voltage being measured, the torque generated by that current will cause the pointer of the instrument to deflect. The amount of deflection is directly proportional to the potential difference between the two points. The voltmeter must be connected in parallel with the circuit in order to measure the voltage.
Symbolic Representation of voltmeter
The voltmeter is a device used to measure the voltage of a circuit. It is symbolized by the alphabet V inside a circle with two terminals. The terminals are connected to the circuit to measure the voltage.
Why is Voltmeter connected in Parallel?
The voltmeter is designed to have a high internal resistance so that when it is connected in series with the circuit, it minimizes the amount of current that flows through the circuit due to the measured voltage. This reduces the potential for the voltmeter to disturb the readings.
The voltmeter is always connected in parallel with the circuit, allowing the same voltage drop to occur across it. The high resistance of the voltmeter, combined with the impedance of the element across which it is connected, creates an overall impedance of the system that is equal to the impedance that the element had. This means that the voltmeter does not obstruct the natural flow of the circuit, and thus provides an accurate reading.
Why Voltmeter has High Resistance?
The voltmeter is designed with a very high internal resistance because it measures the potential difference between two points in a circuit without significantly altering the current of the measuring device. This high resistance prevents current from passing through the voltmeter, ensuring that the correct reading is obtained and that the measurement is not affected by the resistance of the voltmeter itself. By having a high resistance, the voltmeter gives an accurate reading of the potential difference between two points in a circuit.
Types of Voltmeter
The classification of the voltmeter is categorized into three types: digital voltmeter, analogue voltmeter, and electronic voltmeter.
On the basis of its construction, the voltmeter can be classified into the following types.
PMMC Voltmeter
The PMMC instrument operates by utilizing Faraday’s Law of Electromagnetic Induction. This law states that when a current-carrying conductor is placed in a magnetic field, a force is exerted on the conductor. In the case of the PMMC instrument, the force is created by the measurand voltage, which induces a current in the conductor. This current causes the pointer of the meter to deflect, thus providing a visual indication of the voltage.
The PMMC voltmeter uses for DC measurement.
The PMMC voltmeter is a highly accurate instrument with low power consumption. Although it is quite expensive, its range can be increased by connecting a resistance in series with it. This makes it a great choice for a wide variety of applications. Its accuracy and low power usage make it a highly reliable instrument.
MI Voltmeter
The Moving Iron Instrument (MI) is an electrical measuring device used to measure both alternating current (AC) and direct current (DC) voltage. It works by using a coil to create a magnetic field that causes a piece of iron or steel to move, which in turn causes the instrument to deflect. The amount of deflection is directly proportional to the voltage of the coil. MI instruments can be further divided into two types: those with a moving coil, and those with a moving iron core. The former type uses an electromagnet to create a magnetic field, while the latter uses a permanent magnet. Both types are used to measure voltage and current, but the former is more accurate.
Electro-dynamometer Voltmeter
The electro-dynamometer voltmeter is a type of instrument that can be used to measure the voltage of AC and DC circuits. This device uses the same calibration for both AC and DC measurements, making it a versatile and reliable tool. Its design consists of a measure of voltage, a coil, and a rectifier. The coil is used to detect the current, while the rectifier is used to convert AC current to DC current, allowing it to measure both AC and DC voltages. The device is also equipped with a digital display, which allows for accurate readings.
Rectifier voltmeter
The rectifier instrument is a type of instrument used in AC circuits to measure voltage. It works by converting the AC quantity into a DC quantity using a rectifier, which then allows the DC signal to be measured by a Permanent Magnet Moving Coil (PMMC) instrument. This device is essential for accurately measuring voltage in AC circuits.
Analogue Voltmeter
An analogue voltmeter is used for measuring the AC voltage. The magnitude of the voltage is displayed on a calibrated scale via a pointer that has been attached to it. This pointer is deflected as a result of the torque that is applied to it from the voltage being measured. The magnitude of the torque is directly proportional to the voltage being measured.
Digital Voltmeter
The digital voltmeter is an instrument used to measure electrical potential difference between two points in an electrical circuit. It displays the result in numeric form, providing an accurate reading of the voltage in the circuit. This type of voltmeter is used for direct current (DC) measurements, while alternating current (AC) measurements are made with an AC voltmeter. Digital voltmeters are widely used due to their accuracy and convenience.