Voltmeter - Measurement and Instruments

It includes it's symbolic representations, history, types and it's working, applications of Voltmeter.
Can be used for presentations and as a reference too.

1. Measurements and Instruments Mini – Project Presentation Topic - Voltmeter

2. VOLTMETER It works on the principle that the torque is generated by the current which induces because of measured voltage and this torque deflects the pointer of the instrument. The deflection of the pointer is directly proportional to the potential difference between the points. The voltmeter is always connected in parallel with the circuit. Definition:   The instrument which measures the voltage or potential difference in volts is known as the voltmeter.

3. SYMBOLIC REPRESENTATION OF VOLTMETER The voltmeter is represented by the alphabet V inside the circle along with the two terminals .

4. HISTORY The original principals behind voltmeters were established by a Danish physicist named Hans Christian Oersted (1777-1851) in 1820. W hen he discovered that an electric current in a wire produced a magnetic field around it. The first ammeter, which is actually just an extremely sensitive and non-resistive voltmeter, was used by physicist Andre Ampere as early as 1820 to measure current.

5. HISTORY But almost all types of voltmeters are founded off of the models in which the pointers were attached to moving coils, which were developed by French physicist Jacques- Arsene d'Arsonval(1851-1940) in 1882. Since then, their measuring capacity has increased, and some modern day models can measure up to 20,000 volts.

6. APPLICATION OF VOLTAGE READINGS Measurements of voltage are applicable in many situations, but perhaps the most prevalent is it's part in Ohm's Law , which states: V=I*R   when V=voltage[V], I=current[A], and R=resistance[Ohms ] Using this relationship, voltage readings can be used along with another variable to determine another unknown, or by knowing the value of current and resistance we can calculate the voltage(or potential difference) without the use of a voltmeter .

7. Why is Voltmeter connected in Parallel ? The voltmeter constructs in such a manner that their internal resistance always remains high. If it connects in series with the circuit, it minimizes the current which flows because of the measured voltage. Thus, disturb the reading of the voltmeter.

8. Why is Voltmeter connected in Parallel? The voltmeter always connects in parallel with the circuit  so that the same voltage drop occurs across it. The high resistance of the voltmeter combines with the impedance of the element across which it is connected. T he overall impedance of the system is equal to the impedance that the element had. Thus, no obstruction occurs in the circuit because of the voltmeter, and the meter gives the correct reading.

9. Why Voltmeter has High Resistance? The voltmeter is constructed with very high internal resistance because it measures the potential difference between the two points of the circuit. The voltmeter does not change the current of the measuring device. If the voltmeter has low resistance, the current passes through it, and the voltmeter gives the incorrect result. The high resistance of the voltmeter does not allow the current to pass through it and thus the correct reading is obtained .

10. TYPES OF VOLTMETER The voltmeter is classified into three ways. The classification of the voltmeter is shown in the figure below.

11. CLASSIFICATION ON THE BASIS OF OUTPUT The following are the classification of instruments regarding the displays of output reading. Analogue Voltmeter Digital Voltmeter

12. Analogue Voltmeter The analogue voltmeter used for measuring the AC voltage. It displays the reading through the pointer which is fixed on the calibrated scale. The deflection of the pointer depends on the torque acting on it. The magnitude of the developed torque is directly proportional to the measuring voltage.

13. Digital Voltmeter The voltmeter which displays the reading in the numeric form is known as the digital voltmeter. The digital voltmeter gives the accurate result .

14. CLASSIFICATION ON BASIS OF CONSTRUCTION On the basis of the construction, the voltmeter is of the following types . Rectifier Voltmeter MI Voltmeter Electro-dynamometer Voltmeter PMMC Voltmeter Induction type Voltmeter

15. RECTIFIER VOLTMETER Such type of instrument is used in AC circuits for voltage measurement. The rectifier instrument converts the AC quantity into the DC quantity by the help of the rectifier. And then the DC signal is measured by the PMMC instrument.

16. Types of Rectifier based AC Voltmeters Following are the  two types  of rectifier based AC voltmeters. 1. AC voltmeter using Half Wave Rectifier 2. AC voltmeter using Full Wave Rectifier 1. 2.

17. MI Voltmeter The MI instrument means moving iron instrument. This instrument  is used for the measurement of both AC and DC voltage. In this type of instrument, the deflection is directly proportional to the voltage of the coil.

18. MI Voltmeter The moving iron instrument is classified into two types. 1. Attraction Type Moving Iron Instrument 2. Repulsion Type Moving Iron Instrument 1. 2.

19. Electro-dynamometer Voltmeter The electro-dynamometer voltmeter is used for measuring the voltage of both AC and DC circuit. In this type of instruments, the calibration is same both for the AC and DC measurement.

20. PMMC Voltmeter The PMMC works on the electromagnetic effect. The PMMC voltmeter uses for DC measurement. The accuracy of the instrument is very high and having low power consumption. The only disadvantage of the instrument is that it is very costly. The range of the PMMC voltmeter increases by connecting the resistance in series with it .

21. INDUCTION TYPE VOLTMETER Induction type voltmeter uses a single winding to produce flux .The flux produced by this winding is split up into two fluxes , having phase difference with respect to each other. This is done by making a narrow slot in the poles of the electromagnet. It essentially have an electromagnet to produce the required magnetic field.

22. CLASSIFICATION ON BASIS OF MEASUREMENT On the basis of the measurement, the voltmeter is of the following types. AC Voltmeter DC Voltmeter

23. AC VOLTMETER The instrument, which is used to measure the AC voltage across any two points of electric circuit is called AC voltmeter. If the AC voltmeter consists of rectifier, then it is said to be rectifier based AC voltmeter. 

24. DC VOLTMETER DC voltmeter is a measuring instrument, which is used to measure the DC voltage across any two points of electric circuit . If we place a resistor in series with the Permanent Magnet Moving Coil (PMMC) galvanometer, then the entire combination together acts as DC voltmeter.

25. VTVMs and FET VMs These types of instruments can handle both AC/ DC voltages and resistance measurements. These devices use electronic amplifier in between the input and the meter . If this device uses the vacuum tube in the amplifier then it is called as Vacuum Tube Voltmeter (VTVM). VTVM’s are used in high power AC measurements.

26. FET VMs Field Effect Transistor (FET) is a transistor that uses electric field to control the electrical behavior of the device. They are also known as unipolar transistors. Field Effect Transistor based Voltmeter utilizes this property of field effect transistors while measuring voltage.

27. ADVANTAGES OF VOLTMETER The applications of Voltmeter include: It is very useful in finding the voltage of a charge storing device, such as to test the voltage of a battery. For example, a new AAA cell will have about 1.6V, a dying one perhaps 1.1V. A 12V lead-acid car battery will read 12.5V when fully charged, or 14V when being charged by the alternator in a car. If it reads 10V, there is something wrong with the alternator. Verifying the power is on or off to the appliances . They are used to build a continuity tester , with a series battery .

28. ADVANTAGES OF VOLTMETER It can be used just to tell whether there is power in a circuit or not, such as a mains outlet. We can calculate the current by measuring the voltage across a known resistance. This is useful when you don’t have an ammeter. They are used to build an ohm meter, by using a voltage divider with the unknown resistor. They are used to build an ammeter by measuring the voltage across a shunt resistor .

29. THANK YOU