Digital measuring instrument

摘要

A digital measuring instrument which samples at discrete points in time the analog input signals emitted by a measurement transducer of an electrical supply system in a sample and hold circuit. The sampled values are digitized in an analog/digital converter and are then used to determine a system specific quantity such as, for example, the root mean square value or the system frequency. This measuring instrument is suitable for solving the essential measurement value processing tasks occurring in an electrical supply system in a simple manner and with projectable measurement accuracy. This is achieved by the fact that the digital processing unit includes a block for shifting the fundamental and harmonic frequencies to a direct current signal which is proportional to the system specific quantity and a subsequent filter arrangement with a digital low-pass filter for suppressing the frequencies deviating from the direct current signal and a digital band-stop filter for suppressing aliasing frequencies.