| 摘要 |
1492169 Frequency selective voltmeter FELTEN & GUILLEAUME CARLSWERK AG 14 April 1976 [10 May 1975] 15227/76 Heading G1U A frequency selective voltmeter 1, 2, 3, 4, 5, is modified by the inclusion of a switch 11 whereby, for calibration purposes, the filter 2 can form part of an oscillator 2, 3, 6, 10, controlled by a further loop 7, 8 to produce a voltage at the centre frequency of the filter, and having a reference amplitude set by a standard cell 9. Thus, this arrangement replaces the need for a standard A.C. voltage having a frequency accurately set at the centre of filter 2, by the much less stringent need for a standard D.C. cell 9. In the calibrating mode, switch 11 is set to complete the oscillator loop 2, 3, 6, 10 and to isolate the input 1. The amplitude of the signal in the loop is detected 7, compared 8 with the standard cell, and automatically brought 6 to the standard level. Hence, in the calibrating mode, the meter 5 should indicate the standard level, and if it does not it can be appropriately adjusted. |
