Patent GB-1192065-A (GB)
Title: Automatic Data Processing System
IPC: G01N30/86
Filed: 1967-06-01
Abstract: 1,192,065. A-D converters. INFOTRONICS CORP. 1 June, 1967 [11 Oct., 1966], No. 25227/67. Heading G4H. Apparatus for converting the peak values of analogue voltage signals into digital form includes means for automatically calibrating the apparatus. In the embodiment described for the colorimetric analysis of a plurality of colorimeters in which it is required to measure the percentage concentration of chemicals in a solution, the intensity of light shining through a sample of the solution varies the output of a photo-electric cell in the colorimeter. The output from the colorimeter is recorded on a strip chart recorder by a moving slide wire shaft, the latter controlling the pick-off arm of the potentiometer 10 (Fig. 1). A crest detector 12 detects and temporarily stores peaks in the analogue input signal from the potentiometer, the peak voltage being fed via a scaling amplifier 24, a variable function generator 26 (if the relation between light intensity and percentage concentration is non-linear), a potentiometer 82a and contact 61 (closed when, during scanning by a central control, a " digitize request " signal is generated by one of the colorimeters) to a voltage to frequency converter 55 at the central control. A minimum level voltage signal is also fed to the voltage to frequency converter 55 from a potentiometer 79 and the amplitude of the sum of the voltages applied to the converter is converted into a pulse train the frequency of which represents the input voltage. The pulse train is fed by a binary sealer circuit to a gate 95 which is enabled for a reference time interval for the pulses to be accumulated in a binary coded counter 96, the count being displayed and printed. The printer is also fed with signals representing the number of the colorimeter and the number of the sample. The variable function generator 26 generates a function representing the relation between the input voltage and the percentage concentration (by generating a series of straight line segments the slopes of which are variable) so that the output on lead 42 is in linear relation to the percentage concentration. Calibration.-As a preliminary step in calibration the arm 74 of a uniselector 73a is moved to contact 74b so that a fixed voltage v-3 is digitized and displayed. The arm of a uniselector 92 is adjusted so that the output of the binary scaler circuits 86 which results in the nearest correct result being displayed is selected. (The outputs 87-91 having pulse trains of 1, ¢, , # and <SP>1</SP>/ 16  the frequency of the output of the voltage to frequency converter 55.) The position of arm 82a of a vernier scaling member 82 is also adjusted. The uniselector arm 74 is then moved on to a contact 74a when a zero voltage is digitized, the arm of potentiometer 79 being adjusted until the correct result is displayed. The apparatus performs automatic calibration when the arm 74 is on one of the contacts 74e, 74f, 74g. When for example the arm is on contact 74f and five analogue input peaks representing five known percentage solutions are fed in, the first peak initiates a calibration cycle. The second peak corresponding to a zero percentage results in the " offset " control 69 to amplifier 24 being automatically adjusted to match the voltage when arm 74 is on contact 74a. The third signal is used as a buffer between the maximum and minimum values. The fourth signal which represents the maximum concentration results in the " gain " control 70 to the amplifier 24 being adjusted to match the reference voltage v-3 the fifth signal being a check signal.