History of Digital Multimeters How Digital Multimeters Work
Digital multimeters have evolved slowly through history. Early multimeters, which used dials with magnetically deflected hands, were the same as classic ammeters; modern ones use digital displays provided by LCDs or VFDs (Vacuum Fluorescent Displays, Vacuumfluorescentdisplay). Analogue multimeters are not difficult to find on the second-hand market, but they are less accurate, due to the fact that both zeroing and accurate readings from the meter panel are prone to bias. There are analogue multimeters that use vacuum tubes to amplify the incoming signal, and multimeters of this design are also known as vacuum tube voltmeters (VTVM, VacuumTubeVoltMeters) or vacuum tube multimeters (VTMM, VacuumTubeMultimeters). Modern multimeters are now fully digitised and are known exclusively as digital multimeters (DMM, DigitalMultiMeter). In such devices, the measured signal is converted into a digital voltage and amplified by a digital preamplifier, and the value is then displayed directly on the digital display; thus avoiding the bias caused by parallax in the reading. Similarly, better circuitry and electronics have improved measurement accuracy. Whereas older analogue meters had a basic accuracy of between 5[%] and 10[%], modern portable digital multimeters can achieve ±0.025[%], and bench equipment is even more accurate to one part in a million.
Principle of operation of a digital multimeter
The basic circuit of the digital multimeter is a header circuit, which completes the basic function of the input DC voltage (analogue) quantification, and output; other functions generally need to increase the external circuit. Now the multimeter chip, its integration is getting higher and higher, less and less peripheral circuitry, so there are advantages and disadvantages. Advantages: high integration, simple external circuitry, component quality problems caused by quality failures will be much less; disadvantages: chip a bad, replacement cost is high and troublesome, and sometimes the money to replace a chip, can buy another instrument, so the general bad have to scrap.
