GB1419005A - Graphic recording apparatus and method - Google Patents

Abstract

1419005 Control systems for discharge lamps ABBOTT LABORATORIES 23 Feb 1973 9148/73 Heading H2H Apparatus for controlling the amount of light produced by a gas discharge tube, such as a glow modulator used in a scintillation scanner, comprises means for applying a voltage across the tube together with means for producing a signal when current commences flowing through the tube, applying the signal to a further means wherein a second signal is produced a predetermined time after the receipt of the first signal and using the second signal to terminate the production of light by the tube. In use a scintillation scanner 6 is scanned across an area and when a gamma ray is received a signal is produced which is fed to a data processor 10 wherein the signal is converted to a pulse which is inverted in a NOR gate 32 the output of which sets a J-K flip-flop 34 to give a Q output. This output turns on a transistor 38 to turn off transistor 43 giving an output on line 44 from a capacitor circuit 150 previously charged from a constant current circuit 142. The signal on line 44 is applied to an emitter follower transistor 66 which drives a transistor 64 so that current begins to flow in the glow modulator tube 16 in the scanner 6 which current flows for a time sufficient to ionize the gas in the tube. Whilst the Q output of the flip-flop 34 is in the 1 state the #Q output has a 0 state. This state is fed by a line 58 to a NOR gate 82, the other input of which is such that the output of the gate is 1. Transistor 84 thus turns on so that current is suppplied to the capacitor circuit 150 from the constant current circuit 142. The voltage on line 159 and hence on line 44 then increases in a ramp fashion to increase the current flowing in the tube 16. When the current flow in the tube begins to increase a transistor 96 is turned on whereupon the signal on line 104 changes to output of NOR gate 112 to the 1 state to cause the output of NOR gate 82 to change so as to turn off transistor 84. Capacitor 151 in the circuit 150 now begins to discharge through resistor 153 to generate an exponentially decreasing signal on lines 159 and 44 to correspondingly cause a decrease in the current flowing in the tube 16. At the same time so the output from NOR gate 112 changes the state of NOR gate 82 the output from NOR gate 112 causes a signal to be produced on line 126 by way of a multivibrator (NOR gates 120, 118) a predetermined time after the commencement of current flow in the tube 16, this time being set by a variable resistor 129. The signal on line 126 clocks the J-K flip-flop 34 to give a 1 state on its #Q output and a 0 state on its Q output whereupon a NOR gate 86 is operated to cause discharge of the capacitor 151 and the transistors 38, 43 to revert to the states to shunt the signal on line 159 to earth so terminating the light producing current in the tube 16. By controlling the current in the tube 16 in this manner the light output therefrom is claimed to be constant in each period of operation. A fail safe circuit 48 is provided to terminate current flow in the tube 16 in the event of operational failure of the normal control circuit.