A hybrid circuit for producing a three-phase reference sine wave required with PWM inverters is described in this paper. The principle of the circuit is simple and the implementation of the circuit is easy. The circuit has all the features discussed in the literature. The unit built has, apart from the three-phase sine waves, balanced three-phase square and triangular waves. A high-frequency triangular wave already available in the circuit can be used for the PWM control circuitry. The scheme can easily be extended to generate sine waves of any number of phases.

A Novel Three-Phase Reference Sine-Wave Generator for PWM Inverters

The apparatus enables the thermal diffusivity of a wide range of solids to be measured to an accuracy of +or-2% using the Angstrom method. It features a low-frequency sine-wave generator which produces stable sinusoidal temperature conditions at the heater, and a digital phase meter which measures phase directly in degrees with a resolution of 0.1 degrees . A low-noise amplifier and an active bandpass filter are used to improve the signal-to-noise ratio whenever conditions are such that the signals from thermocouples or probes are weak. Results are reported of the thermal conductivity of samples of single-crystal silicon and germanium in the temperature range 300-700K.

https://iopscience.iop.org/article/10.1088/0022-3735/11/9/019/pdf

Apparatus for the measurement of thermal diffusivity featuring a low-frequency sine-wave generator and a digital phase meter

A system has been developed to measure the directivity patterns of full-scale antennas when located in their operational environments. The primary component of this system is an aircraft-towed multifrequency transmitter that is designed to approximate an elementary dipole antenna. An HF and a VHF version of this transmitter provide frequency coverage from 2 to 100 MHz. Techniques have been developed to measure the entire radiation pattern, from the horizon to the zenith, for several antennas simultaneously. Data derived from this system are processed to provide the radiation patterns as contour plots of the measured signal strength on azimuthal equal-area projections. The measurement hardware, data acquisition, and data processing techniques are described, and examples are given of measured and processed data derived from the system.

Measurement of the radiation patterns of full-scale HF and VHF antennas

Differential capacitance displacement transducers (DCDTs) using audo frequency excitation and phase‐sensitive detection are discussed, and their sensitivities are calculated. An inexpensive, low‐power DCDT using a miniature lock‐in amplifier made of integrated circuits is described. The lock‐in amplifier has a digitally controlled phase shift between drive and reference signals, a full‐scale output of ±10 V, and total noise and drift of about 1 mV peak to peak. The DCDT system has a detection limit of 0.01 nm/√H√z, a dynamic range between 60 and 80 dB, and a power consumption of less than 0.75 W. Parts cost for the system is about $200. A simplified DCDT not requiring the full lock‐in amplifier is outlined, and improvements possible in the DCDT design are mentioned where appropriate.

Inexpensive linear displacement transducer using a low power lock‐in amplifier

It is shown that the simple three-phase wave generator presented by V.P. Ramamurthi and R.B. Ramaswami (see ibid., vol.IE-29, no.3, p.235-40 (1982)) is able to exhibit a higher performance when more stringent design considerations are adopted. The results show improvements in linearity and distortion as well as an extension in the frequency range with only small changes in circuit implementation. >

Richer I

Papers

Nonreactive filter converts triangular waves to sines.