• Rectifier type instruments are used for measurement of ac. voltages and currents by employing a rectifier element, which converts a.c. to a unidirectional d.c. and then using a meter responsive to d.c. to indicate the value of rectified a.c.
• The indicating instrument is PMMC instrument, which uses a d’Arsonval movement.
• This method is very attractive since PMMC instruments have a higher sensitivity than the electrodynamometer or the moving iron instruments. The arrangement which employs a full wave
 |
| (Fig) voltmeter using full wave rectifier |
Digital Voltmeter
• A digital voltmeter (DVM) displays the value of a.c. or d.c. voltage being measured directly as discrete numerals in the decimal number system.
• Numerical readout of DVMs is advantageous since it eliminates observational errors committed by operators.
• The errors on account of parallax and approximations are entirely eliminated.
• The use of digital voltmeters increases tile speed with which readings can be taken.
• A digital voltmeter is a versatile and accurate voltmeter, which has many laboratory applications.
• On account of developments in the integrated circuit (IC) technology, it has been possible to reduce the size, power requirements and cost of digital voltmeters.
• In fact, for the same accuracy, a digital voltmeter now is less costly than its analog counterpart.
• The decrease in size of DVMs on account of use of ICs, the portability of the instruments has increased.
Types of DVMs
The increasing popularity of DVMs has brought forth a wide number of types employing different circuits. The various types of DVMs in general use are
(i) Ramp type DVM
(ii) Integrating type DVM
(iii) Potentiometric type DVM
(iv) Successive approximation type DVM
(v) Continuous balance type DVM
No comments:
Post a Comment