Practical Realization of Digital Filters Using Magnetic Delay Elements

Abstract

Many digital filters for process control systems are used in low frequencies. These are not required to be very accurate, but only simple and handy. This paper describes a method for the construction of a digital filter suitable for an on-line process control environment. Magnetic elements are used as delay elements, which are the basic components of digital filters. The most important advantage of the magnetic delay element is the very long delay operation which is possible. This allows filters for very low frequencies to be constructed easily, with a great reduction in size as compared to that of analogue filters. And also, the magnetic delay element has high reliability in a wide range of environmental conditions, and is capable of isolating the input circuits from the output circuits.
As an example, the first-order low pass filters are constructed by the impulse invariant way and the bilinear transformation. The characteristics of these filters are examined. Consequently, it is clear that the errors arising from elements are about 0.3%, and these amplitude characteristics agree approximately with calculated results. In addition, the filter characteristics can readily be altered merely by changing the value of the coefficient or the sampling frequency.