GB1451661A - Control of sewage treatment - Google Patents

Abstract

1451661 Photo-electric measuring apparatus ENGLISH CLAYS LOVERING POCHIN & CO Ltd 24 Sept 1973 [22 Dec 1971] 13713/73 Divided out of 1431541 Heading G1A Apparatus for measuring the rate of settling of suspended solid matter in a sewage liquor comprises a container having an inlet and an outlet, means for supplying sewage liquor to the container, a light source for projecting a beam into the container, a light responsive receiver positioned so as to receive light transmitted through or reflected from the contents of the container, an electrical circuit for detecting a change in response of the receiver caused by movement of the interface between the settling solid matter and the supernatant liquor past the light source and receiver, and means for determining the time interval between the instant when the supply of liquors to the container is stopped and the instant when the change in response of the receiver occurs. As shown in Fig. 1a the container 1 is cylindrical, has an inlet 3, an outlet 4 and an overflow 5, and has mounted in its end-wall an optical head 8 having an end window 9 and containing the light source, a photo-cell for receiving light directly from the source and a photo-cell for receiving light from the contents of the container. As shown in Fig. 3, the container 10 has two compartments separated by a baffle and a photoelectric detector system as shown in Fig. 5 mounted in one compartment. The detector shown in Fig. 5 comprises a light source 22, two light guides 24, 25 and a photo-cell 23. The system shown in Fig. 3 operates as follows. A first timer 13 is initially operated to energize the solenoid of an air lift pump 12 to supply sewage liquor to the container for a pre-set time. At the end of its time interval, timer 13 causes a second timer 14 to be operated, the time period of this timer being related to a given solids content range of the sewage liquor. This time period is for example 100 seconds. A third timer 15, having a time period which is a fraction of that of timer 14, e.g. 10 seconds, is actuated either when timer 14 reaches the end of its period or when a photo-cell operated switch 16 is operated upon the photo-cell detecting the interface. A logic system 17 then operates one of high, normal and low indicators, via a hold/display device 18, depending upon the order in which inputs from the timers 14, 15 and switch 16 reach the logic circuit. Details of the circuitry shown in Fig. 3 are described with reference to Figs. 6 and 7 (not shown).