| 摘要 |
1,135,599. Measuring frequencies. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 19 May, 1966 [22 May, 1965], No. 22256/66. Heading G4H. An unknown frequency f m is converted into a time interval t m and compared with a prescribed time interval t s . In one embodiment (Fig. 1) a gate G v is enabled for a time period t M to pass the frequency signals f m to a counter Z M W 1 . At the end of the time interval a flip-flop is set to enable the counter to count clock pulses of frequency fp in the reserve direction until an output from gate Go indicates that the counter is in its zero position. This output resets the flip-flop so that the output pulse from it to a comparator V when it is in its set state has a length t m = f m - t M /f p At the end of the time interval t M a flip-flop FF s in the device SW 1 producing the fixed time interval is set to enable a counter Z s to count clock-pulses of frequency fp. The clock pulses are fed to a preselection device D which is adjusted to give an output pulse when a count of for example, Z s is attained and so reset the flip-flop FF s . Consequently the flip-flop provides an output from its set state for a time interval t s =Z s /f p . The time interval t m and t s are compared and an output on one of two leads A V and A R obtained depending on which is the greater. In a further embodiment (Fig. 2, not shown) a plurality of input frequencies may be converted into corresponding time intervals and compared with an equal number of pre-selected time intervals under the control of a plurality of devices D, all the devices D being controlled by one counter Z s . In a further embodiment (Fig. 3, not shown) the frequency f m is continuously applied to the positive input of the counter. |
