GB1234494A - - Google Patents

Abstract

1,234,494. Selective signalling. NEW ZEALAND INVENTIONS DEVELOPMENT AUTHORITY. 25 July, 1969 [31 July, 1968], No. 37422/69. Heading G4H. In a digital level meter graduated in dBs the following sequence of operations are performed: (a) the input voltage which is derived from from an input A.C. signal and represents a desired characteristic of that signal, is compared with a reference 0À0 dB, Fig. 5, level of 1À493 v., in order to decide whether its level is positive or negative; (b) the input voltage, by automatically controlled amplification or attenuation, is brought to a level Vin within the range 1À4096 v. to 5À0 v., and (c) either the time taken for an RC circuit to discharge from the input voltage level Vin to a reference level Vo, or the time taken for the circuit to discharge from a level V 10 to the input voltage level, depending respectively whether the original input level was positive or negative (i.e. above or below 1À4096 v.) is measured by counting clock pulses. The level measuring arrangement forms part of a comprehensive A.C. signal measuring device able to measure average, r.m.s., and peak amplitudes, and noise. Automatic amplification or attenuation of the input is effected in response to measuring cycles of the type described above, and a reference precision oscillator is included so that before any measurement is made its output can be digitized and any resulting error used to correct the subsequent measurement.