Principle of Work of Voltmeter da Types of Voltmeter
Wani shine Voltmeter?
Voltmeter shine yanayi amfani da ita don ci gaba da tsari daga biyu. A sani cewa abin da ya zama a kan biyu shine volts. Saboda haka, yana nufin cewa shine yanayi wanda ke ci gaba da tsari daga biyu.
Prinsipal na Yanayi na Voltmeter
Akwai prinsipal mai yawa na voltmeter wanda ke nufin cewa ya kamata a yi tashar karamin biyu inda muke so in ci gaba da tsari. An amfani da tashar karamin biyu saboda an yi voltmeter ta hanyar tafkin da ya fi tsawon kasa. Saboda haka, idan an yi tashar karamin biyu, za a iya ci gaba da tashi da take da yawa, wanda yana nufin cewa an yi tashar karfi.
Idan an yi tashar karamin biyu, za a iya ci gaba da takardun kasa ta karamin biyu da kasa mai yawa na voltmeter, kuma za a iya bayarwa da takardun kasa da ke da shi. Idan an yi tashar karamin biyu, a sani cewa tsari ce da ke da shi, kuma tsari daga voltmeter da kasa ta karamin biyu ya kasance da yawa, saboda haka voltmeter ke ci gaba da tsari.
Idan an yi yanayi na voltmeter mai kyau, an samu kasa da ya fi tsawon infinity, kuma tashin da aka ci gaba da shi ya kasance zero, saboda haka ba za a iya ci gaba da abinci a yanayin. Amma wannan ba a iya samun shi a cikin gagarwa saboda ba a iya samu mutanen da suka da kasa mai kyau.
Tsunukan ko Turanci na Voltmeter
Daga fahimtar na yanayi, akwai turanci na voltmeters, sun hada –
Parmanent Magnet Moving coil (PMMC) Voltmeter.
Moving Iron (MI) Voltmeter.
Electro Dynamometer Type Voltmeter.
Rectifier Type Voltmeter
Induction Type Voltmeter.
Electrostatic Type Voltmeter.
Digital Voltmeter (DVM).
Daga cikin waɗannan turanci, muna da–
DC Voltmeter.
AC Voltmeter.
Don DC voltmetersPMMC instruments suna amfani, MI instrument zai iya ci gaba da AC da DC voltages, electrodynamometer type, thermal instrument zai iya ci gaba da DC da AC voltages. Induction meters ba a amfani ba saboda hanyar ginin, inaccuracy a ci gaban. Rectifier type voltmeter, electrostatic type, and also digital voltmeter (DVM) zai iya ci gaba da AC da DC voltages.
PMMC Voltmeter
Idan an kara tashi a cikin magnetic field, ya faru mekaniki da take faruwa a conductor, idan an kara shi a cikin system mai yawa, tare da yawan coil, pointer yana bude a cikin scale.
PMMC instruments suna da parmanent magnets. Yana da kyau don ci gaban da DC saboda haka deflection proportional to the voltage because resistance constant for a material of the meter and hence if voltage polarity is reversed, deflection of the pointer will also be reversed so it is used only for DC measurement. This type of instrument is called D’Arnsonval type instrument. It has advantages of having linear scale, power consumption is low, high accuracy.
Major disadvantages are –
It only measures DC quantity, higher cost etc.
Where,
B = Flux density in Wb/m2.
i = V/R where V is the voltage to be measured and R is the resistance of the load.
l = Length of the coil in m.
b = Breadth of the coil in m.
N = No of turns in the coil.
Extension of Range in a PMMC Voltmeter
In the PMMC voltmeters we have the facility of extending the range of measurement of voltage also. Just connecting a resistance in series with the meter we can extend the range of measurement.
Let,
V is the supply voltage in volts.
Rv is the voltmeter resistance in Ohm.
R is the external resistance connected in series in ohm.
V1 is the voltage across the voltmeter.
Then the external resistance to be connected in series is given by
MI Voltmeter
MI instruments mean moving iron instrument. It is used for both AC and DC measurements, because the deflection θ proportional square of the voltage assuming impedance of the meter to be constant, so what ever is polarity of the voltage, it shows directional deflection, further they are classified in two more ways,
Attraction type.
Repulsion type.
Where, I is the total current flowing in the circuit in Amp. I = V/Z
Where, V is the voltage to be measured and Z is the impedance of the load.
L is the self inductance of the coil in Henry.
θ is the deflection in Radian.
Attraction type MI Instrument Principle
If an unmagnetised soft iron is placed in the magnetic field, it is attracted towards the coil, if a pointer is attached to the systems and current is passed through a coil as a result of the applied voltage, it creates a magnetic field which attracts iron piece and creates deflecting torque as a result of which pointer moves over the scale.
Repulsion type MI Instrument Principle
When two iron pieces are magnetized with the same polarity by passing a current which done by applying a voltage across the voltmeter than repulsion between them occurs and that repulsion produces a deflecting torque due to which the pointer moves.
The advantages are it measure both AC and DC, it is cheap, low friction errors, Robust etc. It is mainly used in AC measurement because in DC measurement error will be more due to hysteresis.
Electrodynamometer Type Voltmeter
Electrodynamometer instruments are used because they have the same calibration for both AC and DC i.e. if it is calibrated with DC, then also without calibrating we can measure AC.
Electrodynamometer Type Voltmeter Principle
We have two coils, fixed and moving coils. If a voltage is applied at the two coils as a result of which current flows two coils it will stay in the zero position due to the development of equal and opposite torque. If the direction of one torque is reversed as the current in the coil reverses, an undirectional torque is produced.
For voltmeter, the connection is a parallel one and both fixed and moving coils are connected in series with non-inductive resistance.
φ = 0 where φ is the phase angle.
Where, I is the amount of current flowing in the circuit in Amp = V/Z.
V and Z are the applied voltages and impedance of the coil respectively.
M = Mutual inductance of the coil.
They have no hysteresis error,
