| 摘要 |
1,067,734. Digital voltmeters. SOLARTRON ELECTRONIC GROUP Ltd. May 13, 1965 [May 27, 1964], No. 21986/64. Heading G4H. The voltage to be measured is applied across terminals (T, Fig. 1, not shown), and connected by a switch (S1a, S1b to a capacitor (C1) and a resistor (R1) in series. When the switch transfers the capacitor and resistor are connected between earth and an amplifier (A) having a shunt capacitor. The output passes to a level discriminator consisting for example of a difference amplifier (DA) and a relay (DR) having contacts (S2, S4, S5). One of these (S4) causes the relay to oscillate when the input to amplifier (DA) is negative to earth. Another (S5) operates a counter (B), and the third (S2) connects capacitor (C3) either to a standard potential (VR) for charging or to the input of amplifier (A) for discharging. The input to discriminator (D) is reduced to zero by repeated operation of relay (DR). Each operation subtracts the reference charge on capacitor (C3) from the charge on capacitor (C1). The relay (DR) may be replaced by a free-running multivibrator (MV, Fig. 1b, not shown), coupled directly to the counter (B). The output from the multivibrator controls transistor switches (S2a, S2b) through a coupling transformer. The resistor (R1) may be replaced by a constant current device and the period for which the capacitor (C3) is connected to capacitor (C1) may be varied as the output of the amplifier (A) varies. |
