Introduction to Digital Voltmeters:
Introduction to Digital Voltmeters (DVMs) are measuring instruments that convert analog voltage signals into a digital or numeric readout. This digital readout can be displayed on the front panel and also used as an electrical digital output signal.
Any DVM is capable of measuring analog dc voltages. However, with appropriate signal conditioners preceding the input of the DVM, quantities such as ac voltages, ohms, dc and ac current, temperature, and pressure can be measured. The common element in all these signal conditioners is the dc voltage, which is proportional to the level of the unknown quantity being measured. This dc output is then measured by the DVM.
DVMs have various features such as speed, automation operation and programability. There are several varieties of DVM which differ in the following ways:
- Number of digits
- Number of measurements
- Speed of reading
- Digital output of several types.
The DVM displays ac and dc voltages as discrete numbers, rather than as a pointer on a continuous scale as in an analog voltmeter. A numerical readout is advantageous because it reduces human error, eliminates parallax error, increases reading speed and often provides output in digital form suitable for further processing and recording. With the development of IC modules, the size, power requirements and cost of DVMs have been reduced, so that DVMs compete with analog voltmeters in portability and size. Their outstanding qualities are their operating and performance characteristics, as detailed below.
- Input range from + 1.000 V to + 1000 V with automatic range selection and overload indication
- Absolute accuracy as high as ± 0.005% of the reading
- Resolution 1 part in million (1 μV reading can be read or measured on 1 V range)
- Input resistance typically 10 MΩ, input capacitance 40 pF
- Calibration internally from stabilised reference sources, independent of measuring circuit
- 6. Output in BCD form, for print output and further digital processing. Op-tional features may include additional circuitry to measure current, ohms and voltage ratio.