Monitoring and indicating circuit for reverse osmosis filter

Details Monitoring and indicating circuit for reverse osmosis filter Monitoring and indicating circuit for reverse osmosis filter

1990-01-02

1990-06-26

Orsino, Joseph A.

Communications: electrical

Condition responsive indicating system

Specific condition

340607, 210 962, 210 85, G08B 2100

Patent

active

049375571

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 signal causing a red LED to be lit.

REFERENCES:
patent: 3841483 (1974-10-01), Overton
patent: 3990066 (1976-11-01), Malmgren
patent: 4498982 (1985-02-01), Skinner
patent: 4587518 (1986-05-01), King
patent: 4623451 (1986-11-01), Oliver
patent: 4708791 (1987-11-01), Dillard
patent: 4744895 (1988-05-01), Gales et al.
patent: 4762611 (1988-08-01), Schipper
patent: 4784763 (1988-11-01), Hambleton et al.
patent: 4806912 (1989-02-01), Clack
patent: 4849098 (1989-07-01), Wilcock et al.

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