Voltmeter is a instrument used to measure potential difference between two points or to measure voltage. Voltmeter was made by Danish physicist named Hans Christian Oersted (1777 – 1851) in 1820 when he discovered a current in wire produce a magnetic field around it. There are two types of voltmeters
1- Analog Voltmeter
2- Digital Voltmeter
We already discussed analog voltmeter in http://www.electricalengineering4u.com/instrumentation-measurement/electromechanical-instruments/ . Now we discuss digital voltmeter.
digital voltmeter systems:
ramp type digital voltmeter
The main parts of this diagram is Voltage comparator, Clock generator, Ramp generator, Latch and BCD-to-7 segment drivers. Lets discuss its graphical and physical working.
First see that Vi is a straight line and Ramp is a slope all theses things are inputs while comparator output is final output. Lets see how it works. Clock pulses are continuously generating while Vi is high input ramp generator creating a slope where ramp is less than Vi we can see our comparator output is high but when ramp value increase from Vi then comparator output is low and clock pulses stop generating because we already discussed that our Vi is high input but when ramp increases from Vi then it will not remain high. Last thing is latch this is the only difference between analog and digital voltmeter. Decade counters count the value and to hold the previous value we use latch otherwise our previous values overwright.
dual slope integrator dvm:
This circuit is same as previous one only difference is integrator and frequency divider. In this circuit Zero crossing, frequency divider and clock generator are our inputs there is a capacitor inside integrator charging and discharging is main property of capacitor.