SENSOR FOR SENSING CHANGE IN THE AMOUNT OF FLUENT MATERIAL IN A RESERVOIR

摘要

1487679 Sensing fluid level CHRYSLER CORP 24 Oct 1975 [4 Nov 1974] 43905/75 Heading G1N [Also in Division F2] A sensor for sensing a predetermined change in the level of electrically conductive hydraulic brake fluid 12 in each of two reservoirs 10a, 10b comprises resistance probe assemblies 14a, 14b arranged to be normally immersed in the fluid and connected to respective capacitors 20a, b supplied by oscillator 42 with a pulse train voltage V 1 whereby the resultant transient voltage waveforms V 3 , V 4 occuring due to the RC time constant of the capacitorresistance combination are sampled at intervals t 1 -t 2 , t3-t4 and t 5 -t 6 and if either fluid level drops below the probe the resultant voltage transient reflects the increased time-constant and initiates a warning lamp 40 via logic circuit 46, memory circuit 48 and transistor 38. The logic circuit utilizes inverters 74, 76 and a NAND gate 78 whereby if the level of V 3 or V4 is high when the positive excursion of V 2 terminates a logic high passes to flip-flop 80 and thence to enable the transistor. In an alternative embodiment Figs. 3, 4 (not shown) the probe resistances are connected sequentially by a time division multi-plex arrangement to discharge a charged capacitor 84 and the transient waveform is monitored similarly to the foregoing.