Rectifying Electrical Measuring Instrument

a device used to measure the characteristics of an alternating current. It consists of a current rectifier and a permanent-magnet instrument, which measures either the mean value of the rectified current or the relation between the mean values of rectified currents. Semiconducting instruments usually serve as the rectifying element.

A rectifying electrical measuring instrument may be used to measure voltage, current intensity, frequency, phase, or power. In a simplified circuit of this instrument for measuring the intensity of an alternating current, diodes form the double half-period circuit of rectification, and the mean value of the rectified current is measured with a permanent-magnet instrument. The switching of a current into the circuit in a series with a rectifying circuit of added resistance permits the use of this circuit to measure the AC voltage. The scale of the permanent-magnet instrument is usually calibrated in effective values of the voltage or intensity of an alternating current with a sinusoidal form. In actuality, the deviation of the indicator of the permanent-magnet device is proportional to the mean value of the voltage and current intensity. The rectifying electrical measuring instrument is rarely used for measuring power.

As a rule, these instruments are all-purpose multi-limit measuring devices with a high degree of sensitivity. Their disadvantages include a low degree of accuracy and the dependency of readings on the form of the AC curve and on the temperature of the surrounding environment.