ABSTRACT
Different operating principles are used to measure an electric voltage. The mechanical interaction between currents, between a current and a magnetic field, or between electrified conductors was widely adopted in the past to generate a mechanical torque proportional to the voltage or the squared voltage to be measured. This torque, balanced by a restraining torque, usually generated by a spring, causes the instrument pointer, which can be a mechanical or a virtual optical pointer, to be displaced by an angle proportional to the driving torque, and hence to the voltage or the squared voltage to be measured. The value of the input voltage is therefore given by the reading of the pointer displacement on a graduated scale. The thermal effects of a current flowing in a conductor are also used for measuring electric voltages, although they have not been adopted as widely as the previous ones. More recently, the widespread diffusion of semiconductor devices led to the development of a completely different class of voltmeters:
electronic
voltmeters. They basically attain the required measurement by processing the input signal by means of electronic semiconductor devices. According to the method, analog or digital, the input signal is processed, the electronic voltmeters can be divided into
analog
electronic voltmeters and
digital
I U
electronic voltmeters. Table 1.1 shows a rough classification of the most commonly employed voltmeters, according to their operating principle and their typical application field.
