Monitoring and indicating circuit for reverse osmosis filter
US4937557A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jan 2, 1990 |
| Grant date | Jun 26, 1990 |
| Priority date | — |
| Expiry date | Jan 2, 2010 |
Classification
- Technology area (CPC B)Performing Operations; Transporting
- CPC primaryB01D61/12
- WIPO fieldChemical engineering
- WIPO sectorChemistry
Abstract
A monitor and indicating circuit for use with a reverse osmosis filter for signaling the need for servicing of the filter comprises first and second conductivity cells respectively located in the water inlet and outlet pipes of the filter. An AC signal of a predetermined frequency and amplitude is used to drive an op amp whose input resistance comprises the outlet conductivity cell and whose feedback impedance comprises the inlet conductivity cell. Normally, the resistivity of the outlet conductivity cell is substantially larger than the resistivity of the inlet conductivity cell, assuming that the filter is functioning properly. As the ROF fails, the resistivity at the outlet approaches that at the inlet thereby increasing the gain of the variable gain amplifier. The output from the variable gain amplifier is then peak detected and applied to a comparator where it is compared to a predetermined reference voltage. If the output from the peak detector remains below the comparator's reference, the logic means operates to cause a green LED to be illuminated. However, as the filter becomes used, the gain of the operational amplifier approaches unity and the comparator will produce a si…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.