Abstract
Sweep oscillator have been widely used for measuring the frequency characteristics of various devices because of their simplicity and convenience. The characteristics of a sweep oscillator, however, have not been analysed precisely. Measured values are different from the values in the steady state, since the frequency of the sweep oscillator increases exponentially. Measured values should be essentially regarded as the transient ones.
In this paper, at first, it is clarified that the frequency of a sweep oscillator is exactly proportional to the exponential function. The sweep oscillator refered in this paper is a kind of Wien bridge oscillator.
Differential equations which are valid in the first or the second order system to be measured with a sweep oscillator, are normalized and are analysed numerically by Runge-Kutta-Gill method. The error of the first order system is sufficiently small even if a sweep period is substantially short. The error of the second order system is larger when Q of the system becomes higher. Q and the resonant frequency measured with a sweep oscillator are heavily different from the ideal values especially when the sweep period is shorter or Q is higher. The true value of Q may be calculated from the measured value of Q by a monograph showed in this paper. The error of the higher order system may be calculated with the same methods.
The frequency characteristics of systems are normally recorded with a pen recorder and the output voltage of the system is usually compressed by a logarithmic amplifier before recording. The error caused by the AC-DC converter of the logarithmic amplifier is also calculated and the measured value of Q is shown graphically. The error caused by the AC-DC converter is sufficiently small.
