Patent GB-904102-A (GB)
Title: Apparatus to indicate the level of the surface of an electrically conducting liquid in a container
IPC: G01F23/24
Filed: 1959-08-26
Abstract: 904,102. Liquid level gauges. ZEISS - STIFTUNG, CARL. [trading as JENAER GLASWERK SCHOTT & GEN.]. Aug. 26, 1959 [Aug. 26, 1958], No. 29237/59. Class 40 (1). [Also in Group XXXV] Apparatus for indicating or regulating the level of the surface of a conducting liquid, e.g. molten glass, comprises an electrode attached to a piston forced, by hydraulic or pneumatic pressure, to move down against the resistance of a spring until the electrode touches the surface of the liquid. Completion of an electrical circuit including the electrode and the liquid operates a relay circuit to indicate either the position of the piston or the pressure acting on the piston. In the embodiment of Fig. 1, fluid from tank 1 is maintained at a constant high pressure in pipe 4 by means of pump 2 and pressure release valve 5. Pressure buildup on top of piston 9 is slow, due to valve 6, so piston and electrode E move steadily down to the liquid surface. Contact of the electrode with the liquid surface energizes, via relay 19 and the right-hand pair of contacts of 18, motor 15 which drives switch S which closes self-holding contacts 16 to maintain the motor circuit for half a revolution of the switch which takes about 4 seconds, at the same time relay 20 is energized which stops the movement of electrode E by closing valve 7 on the opening of contacts 20 in the circuit of its operating solenoid. During the rotation of switch S contacts 18 are changed over, breaking the original energizing circuit for the motor which is now self-held. Shortly before the completion of the half revolution contacts 17 are made which opens valve 12, allowing the spring pressure to force piston 9 up and the fluid back into tank 1 through restriction 13. Reservoir 14 is provided so that electrode E is suddenly lifted a short distance from the surface in order to break any glass filaments forming on the surface. At the end of the half revolution of switch S contacts 16 are opened stopping motor S. Wheh the pressure in cylinder 9 has fallen to a value corresponding to the required withdrawal of electrode E from the liquid the lower contacts in pressure switch 11 are made and motor 15 energized once again, contacts 17 are opened which closes valve 12 and relay contacts 21, and on completion of half a revolution of switch S contacts 18 are restored to their initial position, contacts 16 are opened, the motor stops, contacts 20 close, valve 7 opens, and the cycle can repeat. If the liquid level has fallen to such an extent that electrode E cannot contact the surface the upper contacts of pressure switch 11 are operated and the cycle continues as if relay 19 had been energized. The liquid level is indicated on the pressure recorder/indicator 10 or alternatively the position of the electrode may be indicated electrically. Preferably if the pressure is to be indicated by an instrument such as indicated at 10 a valve 22 is provided that is open only while the electrode is stationary at the glass surface so that the indicator continuously indicates the liquid level. In an alternative form, Fig. 2 (not shown), the hydraulic pressure source is provided by pressurizing the liquid containing tank from a compressed air supply, the positions of the control valves being modified accordingly, the electrical arrangement otherwise being identical. Regulation of liquid level may be accomplished by inserting a pressure-operated switch in the pressure supply line to measuring instrument 10, the switch operating and controlling liquid feed arrangements when the pressure exceeds a certain value.