Patent GB-1266042-A (GB)
IPC: G01R19/22
Filed: 1969-05-29
Abstract: 1,266,042. Voltage measurement. DANA LABORATORIES Inc. May 29, 1969 [July 9, 1968], No.27304/69. Heading G1U. A system for converting a time varying complex electrical signal to D.C. incorporates a rectifier arrangement 1, a correction signal generator 4 and a combining arrangement 6, output terminals 3 of the rectifier arrangement and correction signal generator being connected to respective input terminals of the combining arrangement, the input signal being applied to respective input terminals 2 of the rectifier arrangement and signal generator. A signal path 9 or 10 respectively is provided to the correction signal generator from an output terminal of the rectifier arrangement and/or the combining arrangement. The system is for use in providing a D. C. representing the absolute average of the fundamental of an A. C. input signal irrespective of in phase odd harmonics, and retains ordinary insensitivity to out of phase odd harmonics and even harmonics, a correction signal being determined from both half cycles of operation. In one embodiment the rectifier arrangement may be a conventional average to D.C. converter (14) Fig. 2 (not shown), a peak averaging converter (13) acting as the correction generator, providing a signal which corrects for the effects of distortion in the input to the converter 14. The outputs of the two converters are summed and filtered at 6 and the final output at 7 is used to control the converter (13) to provide the appropriate amount of correction. In a detailed circuit, Fig.4, diode 60 and load 61 act as the average to D.C. converter. The peak averaging circuit incorporates an inverting transformer 71, and the peaks in both polarities are transmitted by respective diodes 76, 77. The diodes 59, 58 are appropriately biased by potential dividers 56, 68; 55, 69 and the potential from the system output E 7  to pass only those parts of the peaks exceeding a particular output amplitude. The bias is determined in accordance with the particular harmonics to be corrected for. It is shown in the Specification that the average of values greater than #<SP>2</SP>/ 2 e 1  (e 1  being the fundamental peak) or <SP>#</SP>/ #4 #2 #e (#e being the fundamental average) provide proper compensation for the third and fifth harmonics, and the circuit components are chosen to select values in excess of this level. The signals passed by the diodes 59, 58 are added to form the correction signal. This is added to the uncorrected average signal passed via the diode 60 and the whole filtered by the operational amplifier circuit 67. In an alternative circuit, Fig. 6, the input is precision half wave rectified in an operational rectifier circuit incorporating amplifier 106 and rectifying diodes 104, 105. The output E 8  is summed with the input E 1 , to provide conventional full wave rectification at the operational summer filter amplifier 112. A further operational rectifier using amplifier 119 and diodes 117, 118 has gain setting input resistors 113, 114 to which E 1  and E 8  are applied and also receives the system output E 7  as an input. This provides a suitable bias so that only negative going peaks exceeding the bias pass to the rectifier. The rectifier provides the appropriate correction waveform which is inverted at 122 and applied to a further input of the summing filter amplifier 112. In a further alternative embodiment, control of the peak averaging converter may be derived immediatly from the output of the average - D.C. converter rather than from the final output, Fig. 8 (not shown). In another alternative, the average - D. C. converter may be replaced by a peak to peak D.C. converter, Fig. 9 (not shown). In a further arrangement, Fig. 10, half wave rectification may be used to provide the correction signals (half wave rectification will not normally retain basic insensitivity to even harmonics). The input is applied directly to half wave rectifier 300 to provide an average signal at the output of buffer 302, and is applied via biased potential divider 303, 304 to half wave rectifier 305 and buffer 306. The outputs of the two buffers are added and smoothed to provide a corrected signal for the half wave. The bias is obtained from the output of a similar system including diodes 310, 313 operating in the alternate half wave. The two half wave outputs are subtracted to provide the required average output, as may be shown by meter 320.