Reference calibrator of electric voltage within the frequency range 0.1–30.0 mHz
摘要
We consider the park of high-precision instruments for measuring alternating voltage playing the role of working standards of the first and second categories within the frequency range 0.1–30.0 MHz. It is indicated that thermoelectric voltage transducers developed more than 30 years ago are now used as working standards of the first category without alternative despite the fact that they exceeded their service life and do not meet contemporary operating requirements. As an alternative to the sets of thermoelectric converters within the frequency range 0.1–30.0 MHz, it is possible to use the calibrators of alternating voltage. However, in the indicated frequency range, there are no calibrators of alternating voltage that can be used as working standards of the first category. Thus, an N5-10 high-frequency calibrator of AC voltage whose characteristics exceed the requirements to the characteristics of working standards of the first category was developed for operation within the frequency range 0.1–30.0 MHz under voltages of 1·10−3–10V. We describe the concept of design, the characteristics, and operating capabilities of the H5-10 calibrator. In the design of the calibrator, we used the method of equating the amplitude of high-frequency voltage with the known amplitude of low-frequency sinusoidal voltage by the method of amplitude detection. The high-frequency sinusoidal voltage in the calibrator is formed by a frequency synthesizer with the help of the method of direct digital synthesis by using a system of band-pass filters. The accuracy and stability of the amplitude of high-frequency voltage at the output of the calibrator are maintained by an automatic regulation system based on the principle of mutually reciprocal transformations realized with the use of a two-diode integrated assembly of identical Schottky diodes. The low-frequency stable voltage for the base input of the automatic regulation system is formed by a low-frequency calibrator at a frequency of 10 kHz. This calibrator generates an AC voltage within the range 0.1–10.0 V with a harmonic coefficient smaller than 0.01% and an amplitude tuning discreteness of 0.001%. The low-frequency calibrator is constructed on multiplying digital-to-analog converters by the method of digital synthesis of sinusoidal voltage with a stable measure of constant voltage of 2.5 V. The nominal output voltages of the H5-10 calibrator within the range 0.1–10.0 V are reproduced by an automatic regulation system. At the same time, within the range 1–100 mV, they are reproduced by scaling with the use of a voltage divider. The main fields of usage of the developed H5-10 calibrator are the verification and calibration of electronic voltmeters, voltage calibrators, multimeters, and voltage transducers used as working standards of lower categories.