Liquid level switch
US5578994A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | May 25, 1994 |
| Grant date | Nov 26, 1996 |
| Priority date | — |
| Expiry date | May 25, 2014 |
Classification
- Technology area (CPC Y)Emerging Cross-Sectional Technologies
- CPC primaryY10T137/7287
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A piezoelectric liquid level switch is provided which can be made immune to standing wave effects and provides an unequivocal response to liquid contact. The switch incorporates an electrical oscillator circuit including frequency defining elements in both feed forward and feedback circuit paths, the frequency defining element in the feedback path being a piezoelectric crystal device constructed to have a lowest frequency vibration mode in air which is substantially equal to a first frequency defined by the frequency defining element in the feed forward circuit, which mode is suppressed by acoustic coupling of the device to a body of liquid such that a lowest frequency vibration mode of the device when in contact with liquid has a second frequency which is substantially above the frequency of the frequency defining element in the feed forward circuit, whereby positive feedback through the oscillator circuit can occur when the piezoelectric device is in contact with air, but not when it is in contact with liquid, and a threshold circuit for detecting an output from the oscillator circuit at said first frequency. The piezoelectric element is preferably coupled to a column coaxial wit…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.