The digital voltmeter (DVM) displays measurements of dc or ac voltages as discrete numerals instead of a pointer deflection on a continuous scale as in analog devices. Numerical readout is advantageous in many applications because it reduces human reading and interpolation errors, eliminates parallax error, increases reading speed, and often provides outputs in digital form suitable for further processing or recording.
The DVM is a versatile and accurate instrument that can be used in many laboratory measurement applications. Since the development and perfection
DVM have been drastically reduced so that DVMs can actively compete with conventional analog instruments, both in portability and price.
The DVM’s outstanding qualities can best be illustrated by quoting some typical operating and performance characteristics. The following specifications do not all apply to one particular instrument, but they do represent valid information on the present state of the art:
(a) Input range: from ± 1.000000 V to ± 1,000.000 V, with automatic range selection and overload indication
(b) Absolute accuracy: as high as ±0.005 per cent of the reading
(c) Stability: short-term, 0.002 per cent of the reading for a 24-hr period; long-term, 0.008 percent of the reading for a 6-month period
(d) Resolution: 1 part in 106 (1 microV can be read on the 1-V input range)
(e) Input characteristics: input resistance typically 10 Mil; input capacitance typically 40 pF
(f) Calibration: internal calibration standard allows calibration independent of the measuring circuit; derived from stabilized reference source
(g) Output signals: print command allows output to printer; BCD (binary-coded-decimal) output for digital processing or recording
Optional features may include additional circuitry to measure current, resistance, and voltage ratios. Other physical variables may be measured by using suitable transducers.
Digital voltmeters can be classified according to the following broad categories:
(a) Ramp-type DVM
(b) Integrating DVM
(c) Continuous-balance DVM
(d) Successive-approximation DVM