Patent GB-1343465-A (GB)
Title: Particle counting system
IPC: G01N15/12
Filed: 1971-04-22
Abstract: 1343465 Particle counting apparatus GENERAL SCIENCE CORP 22 April 1971 [28 April 1970 (2)] 10705/71 Heading G1N A particle counting system includes a photosensitive metering technique to determine the volume of liquid which is to be analysed. In a blood cell counting system a sample flask 10 is connected to a conductivity cell (14) Fig. 2 (not shown) including an aperture across which electrodes 36, 38 are connected and a vent aperture opened and closed by solenoid energized stopper 76 to allow the cell (14) to be purged or to allow the sample to flow through the cell(14), through tube 16 to waste bottle 18 under the control of suction pump 20. Two photo-sensors 28, 30 and light sources 32, 34 are disposed along the pipe 16 to detect the flow of sample therealong and apply signals to the logic circuitry 26 to control the counting period. Operation Fig.6 After connecting the sample flask 10 to cell (14), Fig.4 (not shown) the count control is activated to reset counter 132 and energize the vent control 148, to close the vent passage in the cell (14), and pump 20. When the fluid flow in pipe 16 reaches start photo-sensor 136 a signal is derived therefrom and applied to gate 134 to allow pulses from trigger circuit 128, triggered by the signals from the energized electrode pair 36, 38 due to the passage of cells through the aperture in the cell (14) to pass to counter 132. When the fluid in pipe 16 reaches the stop photosenser 138 a signal is applied to block gate 134 to stop the count and to the vent control 148 to open the vent passage in the cell (14) to allow the latter to be purged of sample fluid. Count interval verification The signal from the start photo-senser 136 is applied to trigger timer 140 which generates a pulse of duration T1 equal to the minimum interval for a valid count. At the termination of time T1 a second timer 141 applies a pulse of duration T2 to the gate 142, this interval representing the tolerance range of the count, to close it so that the presence of a stop signal from photo-senser 138 does not pass through the gate 142 to activate indicator 144. If a stop signal is received before or after the generation of T2 gate 142 passes the signal to activate indicator 144 e.g. due to a blocked aperture. Amplifier 40 is also continuously monitored by baseline detector 146 which is responsive to the low frequency spectrum due to gas bubbles in the sample to activate indicator 144. Sample flask coding A red blood cell sample flask includes a flange, Fig.5 (not shown), which when the flask is connected to the cell (14) activates a switch 125  which sets the threshold circuit 120 to the level corresponding to red cell count. A white cell sample flask has no flange and the switch is in the position to set the threshold circuit corresponding to a white cell count. The switch also sets the decimal point on a digital counter display, Fig.3 (not shown). Waste bottle detector The waste bottle 18 includes a pair of electrodes 152 which operate overflow indicator 156 when the bottle is full and activate vent control 148 to remove the stopper from the vent passage and cease the flow. Calibration A sample flask containing a non-particulate saline solution is connected to the cell 14 and the fluid is drawn through the system. Calibration oscillator 122 is triggered to apply pulses to amplifier 40 which pulses are processed in the same way as the blood cells. The oscillator 122 is stopped by a signal from timer 140. Automatic threshold plotter Fig.8 (not shown). In order to determine the required threshold level of circuit 120 a red blood cell sample is first passed through the cell (14) and the pulses from the trigger circuit 128 are applied to a one shot multivibrator. The output of the multivibrator is applied to a count rate detector the D.C. voltage output of which is applied to the Y-axis of an XY plotter. A ramp voltage is applied to the X-axis of the plotter and also to the threshold circuit 120 and a plot obtained. The process is repeated for a white cell sample and a further XY plot obtained. The required threshold level is obtained from inspection of the plots Fig.9 (not shown).