| 摘要 |
1,251,754. Peak voltage measurement. E.I. DU PONT DE NEMOURS & CO. Jan. 31, 1969 [Feb. 9, 1968], No.5475/69. Heading G1U. A system for measuring the maximum amplitude of a pulse of energy, such as a light pulse 8, incorporates a transducer 9, such as a photomultiplier, which produces an electric signal proportional to the pulse, coupled to an operational amplifier 19 which has an automatic range changing system 22 coupled in feedback relation to it, by which the output from the amplifier is attenuated in a given ratio whenever the amplifier output reaches a predetermined value. A first indicating device 26 is coupled to the range changing system to indicate whenever the amplifier output reaches the predetermined value. A memory 28 is coupled to the amplifier output via diode 27 and retains the maximum amplitude of the output signal following the last attenuation, the amplitude being indicated by a second indicating device 33. The output from the photo-multiplier 9 takes the form of an uni-directional current pulse whose amplitude depends only on the size of the input light pulse 8 and the photo-multiplier supply 10. This current is smoothed by a filter circuit 11 which incorporates transistor switches 16-18 which are progressively switched in as the current increases to shunt the resistors 13, 14, 15, so that resistance is decreased as the current increases, so that a high voltage drop is not developed across the filter. The filter output is passed to the amplifier 19 whose output controls a pulse generator 23 to release a pulse when a given amplitude is reached. This pulse is applied to logic circuit 24 which switches the controlled resistance circuit 25 to reduce the amplifier gain by e. g. a factor of 10. The pulse also switches on the transistor 29 to discharge the capacitor 28 which normally is fed by the amplifier output via the diode 27. Indicator 26 monitors the condition of the range changing circuit, while amplifier 32 and indicator 33 detect the voltage on the capacitor 28. A switch 30 enables the capacitor to be discharged between measurements, at which times the attenuator circuit must also be returned to zero setting. The amplifier 19 is also provided with a feedback circuit 27 designed to eliminate the effect of the standing current in the photo-multiplier which appears in the absence of input pulses. This circuit detects and stores the amplifier output in the absence of input pulses to the photomultiplier and feeds back an appropriate current to cancel the standing current when input pulses occur. The system is calibrated by irradiating the photomultiplier with the output of a lamp of known magnitude and adjusting the supply 10 until the appropriate reading is achieved. |
