Saturday, 16 March 2013

INTRODUCTION TO DVMs



Digital Voltmeters (DVMs) are a special case of A/Ds. 
DVMs are general purpose instruments commonly used to measure voltages in labs and in the field.  DVMs display the measured voltage using LCDs or LEDs to display the result in a floating point format.They are instruments of choice for voltage measurements in all kinds of situations.
They display measurements of both AC and DC voltages as discrete numerals.
Analog measuring instrument is current instrument where as digital measuring instrument is a voltage measuring instrument
Types of DVMs
1)Ramp type
2)Dual slope
3)Successive approximate type
DVM = A/D converter + digital read out

Resolution of DVM
          It is small incremental change in input which can be detected. It depends on number of digits
          Resolution = 1 / 10N   N = number of full digits
Sensitivity
The minimum input voltage level that can be sensed and displayed by DVM
          Sensitivity = resolution * range
Number os sesitivities of DVM = number of ranges
Features of DVM
1)They offer superior resolution of order of 1: 106
2) improved accuracy = + 0.005%
3) parallax errors are eliminated
4) more portable
5) They offer very high input resistance in the range of mega ohms.So loading errors are minimized
6) The output is available in digital form. So further processing is made possible

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