Contamination level indicator

Claim 1

An apparatus for providing a continuous indication of a level of contaminant in a fluid comprising: a working fluid system; a by-pass connected to said working fluid system; flow rate control means in said by-pass whereby fluid flow through said by-pass can be controlled; a pervious barrier in said by-pass, said barrier having pores of a known size therein; a slide valve in said by-pass wherein fluid flow through said by-pass can be directed to one of a first or second sides of said barrier; and a logic circuit responsive to pressure upstream of said barrier and to time whereby a rate of build-up of contaminant of particle size greater than said known size of said pores can be measured; said logic circuit being operatively connected to said slide valve such that at a predetermined criterion said slide valve is actuated to redirect fluid flow to the other side of said barrier whereby contaminant is back flushed from said barrier whereafter another measurement is commenced, said logic circuit being adapted to process said rate of build-up and to average said rate of build-up over a plurality of cycles to provide an indication of the level of contaminant in said fluid, said logic circuit comprising means for compensating for variations in the viscosity of the fluid, the compensating means comprising means for obtaining, at different times, first and second values representative of a variable quantity, and means for deriving a ratio of said first and second values, the variable quantity being a function of the fluid flow rate through the barrier and the pressure drop across the barrier.

Claim 2

An apparatus for providing a continuous indication of a level of contaminant in a fluid comprising: a working fluid system; a by-pass connected to said working fluid system; flow rate control means in said by-pass whereby fluid flow through said by-pass can be controlled; a pervious barrier in said by-pass, said barrier having pores of a known size therein; a slide valve in said by-pass wherein fluid flow through said by-pass can be directed to one of a first or second sides of said barrier; and a logic circuit responsive to pressure upstream of said barrier and to time whereby a rate of build-up of contaminant of particle size greater than said known size of said pores can be measured; said logic circuit being operatively connected to said slide valve such that at a predetermined criterion said slide valve is actuated to redirect fluid flow to the other side of said barrier whereby contaminant is back flushed from said barrier whereafter another measurement is commenced, said logic circuit being adapted to process said rate of build-up and to average said rate of build-up over a plurality of cycles to provide an indication of the level of contaminant in said fluid, said logic circuit comprising means for compensating for variations in the viscosity of the fluid, the compensating means comprising means for obtaining, at different times, first and second values representative of a variable quantity, and means for deriving a ratio of said first and second values, the variable quantity being a function of the fluid flow rate through the barrier and the pressure drop across the barrier.