GB899145A - Improvements in or relating to adjusting means for colorimeter-recorders - Google Patents

Abstract

899,145. Photo-electric measurement of colour. TECHNICON INSTRUMENTS CORPORATION. Oct. 13, 1959 [Oct. 27, 1958], No. 34665/59. Class 40(3). In a photo-electric colorimeter having a recorder in which a predetermined characteristic of a liquid under examination is made in response to the operation of a selfbalancing electric system including means for balancing first and second predetermined voltages for establishing a base or reference line of the recording in a predetermined position in accordance with the known characteristic of a standard liquid, an arrangement operable in conjunction with the selfbalancing system of the recorder automatically re-establishes the predetermined position of the base line in the event of deviation therefrom during the operation of the recorder. The colorimeter 10 comprises a light source 12 with mirrors 18, 20 and apertured members 26, 36 transmitting beams through a reference liquid and the liquid to be examined in tubes 28, 38 associated with photo-cells 30, 40 respectively connected to potentiometers 44, 46 of loops L1, L2 from which voltages are applied in opposition to a circuit 54 converting the D.C. input to alternating current and via a transformer 56 and an amplifier 58 to the winding 72 of a two-phase motor 78 which rotates the shaft 84 so that a threaded nut 86, held against rotation, moves a tapping pointer 59 over potentiometer 44 until the electrical outputs from the loops L1, L2 are balanced. At the same time a second nut 86<SP>1</SP> on the shaft 84 moves a pointer 88 over a record sheet 90 traversed continuously in the direction of the arrow 92. For initial calibration a sample liquid corresponding to 100% transmission is placed in the tube 28 and is passed through the apparatus, and the tap 68 adjusted so that the pointer 88, records a 100% transmission. A light-obstructing member is then interposed in the path of beam 32 to the tube 38 and the photo-cell 40 and the tap 50 on potentiometer 48 adjusted so that the stylus 88 records the zero position. The lightobstructing member is then removed and the tap 68 readjusted so that the stylus 88 is at the 100% position. These adjustments are repeated until the pointer 88 takes up the 100% and 0% positions on the chart 90. A tap 96 on a potentiometer 94 is adjusted to correspond to the portion of the tap 59 for the 100% position. The standardizing operation is controlled by a timing device 100 comprising notched discs 124, 126 driven by a motor 120 at the rate of 1 revolution per hour. Normally the switches 106, 128 are open, but the engagement of arm 107 with the notch 125 energizes a solenoid 104 actuating a valve 17 allowing the standard reference liquid to pass from input 110 to outlet 15 and through the container 5 to the tube 38 of the colorimeter 10. Ten minutes later the arm 129 of the switch 128 engages the notch 127 of the disc 126 and operates relay 130 so that contact arm 64 is moved to the left to connect the tapping point 96 to the input of the converter 54 and to complete a circuit to the plate 144 of magnetic clutch 142. At the same time the arm 107 is raised to open switch 106 so that the solenoid 104 is released and the valve 17 returns to its position shown to re-establish the flow of the liquid to be analysed to the flow chamber 5 and subsequently to the tube 38. Normally the outputs from the loops L1, L2 will be balanced, but if the voltage at the tapping point 68 has changed and the position of the base line altered, the motor 78 will rotate in one or the other direction to restore the balanced outputs and return the voltage at the tap 68 to its former value by deriving a compensating resistance from a rheostat 150, and at the same time causing the pen 88 to return to the predetermined 100% base line. The standardizing operation persists for a period of ten minutes at the end of which the liquid to be analysed is again being circulated through the tube 38. Specification 774,711 is referred to.