GB1265417A - - Google Patents

Abstract

1,265,417. Measuring colour temperature photo-electrically. INSTITUT FUR PLASMAPHYSIK G. m. b. H. Aug. 6, 1969, No.39462/69. Heading G1A. Tne colour temperature of a radiating body is measured photo-electrically by adjusting the intensity of two wavelength ranges equally be means of an attenuating device so that the intensity in one wavelength range is brought to a predetermined value when the intensity in the other wavelength range is measured to provide an indication of colour temperature. In its simplest form a first colour filter is introduced into the beam and an iris diaphragm operated to attenuate the beam until a calibration value is obtained on a meter connected with a photo-electric device. The first filter is removed and a second filter introduced when the meter reading will correspond to colour temperature. In the embodiment shown the radiation beam 1 is focused through a beam-splitting device 7 on to photo-resistors 21, 23 which are connected in bridge networks 25, 39 respectively. Colour filters 13, 15 and baffles 17, 19 are provided in each path 9, 11 respectively. Bridge network 39 has its output connected through amplifier 51 to motor 53 which alters the aperture of iris diaphragm 55 thereby varying the beam intensity so that the resistance of photo-resistor 23 alters to balance the bridge. When the bridge is balanced the colour temperature can be read directly from meter 37 connected to the output of bridge 25. In a modification a single bridge network may be used and is connected to the photo-resistors in turn by means of a changeover switch. In a further modification adjustable diaphragms are used in both the paths 9, 11 and are operated together. The beam-splitting device may be a semi-permeable mirror, a prism, a dichroic mirror or a diffraction screen and the attenuator may comprise a wedge filter or polorizers, rotatable with respect to one another. It is also possible to use an adjustable attenuator in the path 9 and a null reading meter so that the colour temperature is measured by the setting of the attenuator. In practise the components for paths 11, 9 are arranged in tubes 57, 59 respectively, the latter being pivotally mounted so that eye-piece 69 can be used to align the instrument with the body, Fig. 2. In another embodiment, Fig. 4 (not shown), two photo-multipliers are used as detection devices and are connected to a meter and to a control mechanism respectively. The control mechanism consists of an aperture adjusted by a servomotor, and a control circuit which alters the voltage supplied to both photo-multipliers to keep the output of the reference photo-multiplier constant. It is stated that this additional control gives a faster response time.