The Working Principle of a Digital Multimeter
The History of Digital Multimeters
Digital multimeters have evolved gradually over history. Early multimeters used a dial with a pointer deflected by a magnet, similar to the classic galvanometer. In modern times, digital displays provided by LCD (Liquid Crystal Display) or VFD (Vacuum Fluorescent Display) are adopted. Analog multimeters are not difficult to find in the second-hand market, but they are not very accurate. This is because both zero adjustment and accurate reading from the instrument panel are prone to deviations.
Some analog multimeters use vacuum tubes to amplify the input signal. Multimeters with this design are also known as Vacuum Tube Volt Meters (VTVM) or Vacuum Tube Multimeters (VTMM). Modern multimeters are all digital and are specifically called Digital MultiMeters (DMM). In this kind of device, the measured signal is converted into a digital voltage and amplified by a digital preamplifier, and then the value is directly displayed on the digital display screen. In this way, the deviation caused by parallax during reading is avoided. Similarly, better circuit systems and electronics have also improved the measurement accuracy. The basic accuracy of old analog instruments is between 5% and 10%, while modern portable digital multimeters can achieve an accuracy of ±0.025%, and bench equipment can even reach an accuracy of one part per million.
The Working Principle of Digital Multimeters
The basic circuit of a digital multimeter is a meter head circuit, which performs the basic function of quantifying the input DC voltage (analog quantity) and outputting it. Other functions generally require the addition of external circuits. Nowadays, the chips of multimeters have an increasingly higher degree of integration, and there are fewer and fewer peripheral circuits. This has both advantages and disadvantages.
Advantages: With a high degree of integration and a simple external circuit, there are many fewer quality failures caused by component quality problems.
Disadvantages: Once the chip is damaged, the replacement cost is high and it is troublesome. Sometimes, the money spent on replacing a chip is enough to buy another instrument. So, generally, when it is broken, it has to be scrapped.
