Patent GB-818086-A (GB)
Title: Galvanometer digitizer
IPC: H03M1/00
Filed: 1956-05-25
Abstract: 818,086. Photo-electric measuring systems. ESSO RESEARCH & ENGINEERING CO. May 25, 1956 [July 26, 1955], No. 16260/56. Class 40 (3). The invention relates to means for translating voltage or current peaks into a pulse series which are counted to give an indication of the peak value. It may be applied to the detection of voltage maxima developed in a mass spectrometer. According to the invention the voltage (or current) whose maxima are to be determined is applied to a mirror galvanometer whose mirror 5 reflects collimated light from source 1 in a direction varying between zero position 7 and maximum position 8. A light modulating means is arranged in the plane of the reflected beam and directs light from alternate small areas thereon to a photo-cell to produce a series of electrical pulses which can be summed. In the arrangement shown in Fig. 1, a wedge 10 of transparent material has its front face 11 in the plane of the beam divided into alternate transparent and opaque areas and it leads light passing through the transparent areas to a photo-cell 17. Application of a transient voltage to the galvanometer will cause deflection of the light beam from position 7 up to a maximum position and back and the number of pulses produced in the photo-cell output will give a measure of the voltage maximum. In an alternative light pulsing means reflected light from the galvanometer is directed on to a curved mirror having alternate reflecting and transmitting or absorbing sections, from the reflecting sections of which light is brought to a focus at a photo-cell (Fig. 2, not shown). In another embodiment a lighttransmitting rod provided with spaced opaque bands along its length is arranged so as to be scanned by the deflected beam and light passing into the rod when the beam is between bands is directed along the rod to a photo-cell (Fig. 3, not shown). In a further embodiment the light sensitive element itself 42 (Fig. 4), is combined with the modulating means in that its surface extends over the length of the light beam reflection range and is masked or marked so as to provide alternate masked and effective areas. Fig: 4 also shows how the invention may be applied to the determination of voltage maxima developed at the ion collector 50 of a mass spectrometer. The voltage peaks so generated are amplified at 51 and applied to terminal 63 of relay 52 normally biased as shown and also through noise filter 56 to differentiating circuit 53, 54. The output of the differentiator is derived from an adjustable tapping point or resistor 54 so that the sensitivity of the system may be adj usted and is fed through a top and bottom cutting amplifier 57 to a phase-sensitive rectifier 58 which also inserts a suitable D.C. level in the signal fed to relay coil 61. The effect of this circuit is such that on arrival of a voltage peak signal from amplifier 51 an energizing voltage is fed to coil 61 to cause the signal to be applied to galvanometer 65 before it reaches its peak value. The galvanometer mirror therefore turns from its zero (rest) position to a position representing the peak value of the signal. Immediately the peak signal value has passed reversal in polarity of the differentiator output causes relay 52 to drop out and the mirror to fall back to its zero position. The pulses supplied to the counter are thus always proportional to the level of the voltage peak above zero. The light interrupting arrangement may be made in such a way as to provide a logarithmic instead of a linear scale for the counter output.