A voltmeter, also known as a voltage meter, is an instrument used for measuring the potential difference, or voltage, between two points in an electrical or electronic circuit. Some voltmeters are intended for use in direct current (DC) circuits; others are designed for alternating current (AC) circuits. Specialized voltmeters can measure radio frequency (RF) voltage.
1. analog voltmeter, analog voltmeter are rotating device rotating frame Baazafh a resistance in series with the coil (frame) is used as a voltmeter.
2. The digital voltmeter: digital measurement devices due to the lack of moving parts, very high lifetime (if using them correctly) are entitled to physical factors such as vibration, humidity, air cleanliness and ... not case sensitive .