Patent GB-966975-A (GB)
Title: Method of and means for comparison of two electrical potentials for purposes of photometry and the like
Inventor: BIERMANN MARKUS
IPC: G01C1/02
Filed: 1960-12-08
Abstract: 966,975. Voltage measurement. CONTINENTAL ELEKTROINDUSTRIE A.G., [trading as CONTINENTAL ELEKTROINDUSTRIE A. G. ASKANIA-WERKE]. Dec. 8, 1960, No. 42288/60. Heading G1U. [Also in Divisions G3, G4 and H4] In photo-electric apparatus for aligning optical instruments, the amplitudes of relatively fixed phase maxima of a periodic voltage signal are compared by feeding the entire signal to a mixer over a single channel, feeding to the mixer a reference voltage of periodic or alternating waveform having the same frequency as the signal and in fixed phase relation thereto; multiplacatively mixing the signal and reference voltages and measuring the time average of the product. A kinetheodolite (Fig. 1) comprises a telescope 1 swinging about horizontal axis 1 in trunnions 4, 5 rotatable about axis 3 of baseplate 6 adjustable by tripod screws 11 on lower baseplate 12 with reference to level bubbles 7, 8 and a plumb bob (not shown) optically observable at 73. Calibrated circles are observable by microscope 9; and the object is viewed in eyepiece 10. In Fig. 2, reticle 16 of the telescope is followed by glass cube 17 diagonally split along plane 18 with an interference mirror coating, so that one portion of the reticular image is viewed in the eyepiece and another is transmitted to objective 19 of a transducer unit 15 coupled at 21 to the eyepiece end 20 and clamped to the objective end at 23. Objective 19 forms an image in plane 37 of an edge 38 of image splitting prism 24 (Fig. 3) and the partial images are cyclically admitted by a cylindrical shutter 25 revolving at velocity w and collector prisms 26 to a point of the cathode of an electron multiplier tube 27. Shutter 25 is gearedly driven from D.C. motor 32 together with generator 33 of an alternating references signal y(t). Boundary planes 25<1>, 25<11> of the shutter include an angle # so that for one revolution the imaged light fluxes A, B are withheld from the multiplier over angle # # between alternate exposures. The potentials a corresponding to light flux A and b corresponding to light flux B where a > b are shown as the waveform of Fig. 4a plotted as waveform x(t) against time and on differention to x<1>(t) as the waveform of Fig. 4b, and it is shown that for pointing of the telescope precisely at a luminous object a = b and if the alternating waveform xt is multiplicatively mixed, with an alternating reference waveform yt (or the waveform x<1>t by a reference waveform y<1>t) of fixed predetermined phase relation thereto, it is shown that the time averaged product of the measuring and reference potentials is proportional to (a + b) (a - b) and the phase difference with a D.C. component zero when a = b, provided that x contains only even harmonics and y only odd harmonics of the fundamental. The reference waveform may be a square wave. Alternatively (Fig. 5) the dual light fluxes I and II alternately fall on the cathode 46 of multiplier 45 through shutter plate 40 apertured at 40<1>, 41 and driven from battery operated motor 43. The battery excites transducer 48 to generate voltage for the multiplier electrodes, whose output is amplified and multiplied by the reference voltage from generator 44 driven from the motor in network 51. The averaged D.C. component #xy of the product is recorded at 93 and indicated at 52, to indicate by null the direction of the telescope directly upon a luminous object. The phase of the reference signal is adjustable by mutual displacement of the rotary and stationary elements of generator 44. The multiplicative mixer 51 may embody a Hall plate (Fig. 6 not shown) and the voltage transducer assembly may be housed at 35 on the underside of the telescope, with cable connections to a remote amplifier, multiplier, and indicator assembly. The multiplier power may be derived from a transistorised blocking oscillator and a selective amplifier for the multiplier output may also be transistorised (Fig. 5a not shown). Instrumentation is provided for setting amplifier gain and supply voltage monitoring. Multiplicative mixing and indication may be combined in a multiple coil dynamometric-measuring instrument (Fig. 7 not shown). The multiplicative mixer output may be amplified and applied to a servomotor geared to maintain the theodolite aligned on an object, or similarly to keep a telescope aligned on e.g. a star (Fig. 8 not shown). In analytical photometry (-Fig. 9) a monochromatic light source 77 is focused by reflector 78 on a beam splitting prism 79 whose emergent rays traverse receptacles 75, 76 containing a reference medium and a substance to be examined. The emergent rays are combined in prism 84, and the combined ray is modulated by revolving shutter 85 and focused by reflector 89 on light sensitive element 88. The output is amplified and multiplicatively mixed at 91 with the reference output of a generator 87 driven with the shutter. The mixer output may operate an indicator or a recorder, or a regulator varying passage of a selected fluid into receptacle 76 until equality of light absorption is achieved at zero output. In precision measurement, (Fig. 10) illuminated graduations 101 of a scale are focused by lens 102 in image planes 103, 104 through optical micrometer 105 comprising a plane parallel glass plate rotatable by mechanism 106 about axis 107 to shift the image of the graduations without rotation of ray trace 108, in which semireflecting prism 109 is interposed. An eyepiece allows observation of the scale by reflection in prism 109 through lens 111; superimposed on a scale 110 showing the position of micrometer plate 105. The undeviated ray through prism 109 passes through aperture 115 and enters image splitting block 114 whose diagonal is half coated up to a limiting edge 130 with reflecting material; the emergent rays A and B passing through reflectors 120, 121, 122 to prism 123, rotating shutter 125, collector prism 126 and photoelectric device 124 whose output is amplified and multiplicatively mixed in wattmeter movement 129 with a reference voltage derived from generator 128 driven with the shutter. Micrometer 105 is adjustable to superimpose an image 101 for scale graduation mark precisely on edge 130 and symmetrically of aperture 115 i.e. in alignment with ray trace 108, the displacement is indicated by scale 110 and alignment by null indication of 129. Multiplicative mixing may be achieved by exciting a Ferraris motor with the photo-electric output and the reference signal; the motor drive being utilized for indication or alignment servo operation. (Figs. 8a, 8b not shown) The respective signals may be modulated on carrier waves if their frequency is low.