| 摘要 |
1,202,073. Product; difference computing. AMERICAN OPTICAL CORP. 22 Nov., 1967 [1 Dec., 1966], No. 53273/67. Heading G4G. Alternating current analogue signals are combined to a third signal representing product or difference by applying one such signal (or a combination thereof) to a switch input generating a pulse control signal from the other thereof to control the switch operation between conducting and non conducting and filtering the switch output to produce the required signal. In Fig. 1, signals V A and -V B of identical frequency in antiphase (e.g. from the photo-cell outputs of a dual beam spectrophotometer) are applied to inputs 10, 12 from which they are algebraically added at junction 14 to produce error signal V s applied to a switching circuit (Fig. 3, not shown) comprising a transformer fed biased amplifier having a pulsed transistor alternately connecting and disconnecting the input to earth. Input V A is also amplified to constant amplitude V c which is applied to control the frequency of the output V o of a relaxation oscillator 20 according to its instantaneous voltage values, to drive a oneshot multivibrator 22, whose output is thus a sinusoidally frequency multiplied pulse train, to pulse the switch 16 (Fig. 2, not shown), whose output is integrated in low pass filter 24, to a direct voltage V F which is shown by mathematics to be combined of a constant voltage V R and a voltage proportional to the product V c , V s . Amplification by differential D.C. amplifier 26 receiving a voltage V R produces an output proportional to V c , V s and thus to (V A -V B ) since V C is constant. This signal may be applied to a null balance servosystem controlling V A and -V B for null error. Alternatively the output represents the product of (V A -V B ) V C where V C is proportional to V A . Where V A and V B are applied directly to the relaxation oscillator and the switch respectively, the output is proportional to the product V A , V B . |
