US 4,775,833 A · Lodged debris detector for a particle analyzer

Abstract

A debris detector for a particle counter, such as a blood cell counter, of the COULTER (R) type. When a particle, or transient debris, passes through the sensing orifice of the particle detector, a voltage pulse occurs; whereas, when debris lodges in or against the orifice of the particle detector, a d.c. voltage shift occurs. The voltage at the orifice is capacitively coupled to an amplifier and the output of the amplifier is integrated. The capacitor coupling the orifice voltage to the amplifier causes an undershoot voltage at the trailing edge of each particle or transient debris pulse, such that a zero average voltage is applied to and, hence, from the amplifier for each voltage pulse. The integrated voltage is applied to a voltage comparator to provide an output signal therefrom whenever the integrated voltage exceeds a reference voltage. The comparator output signal is provided to a delay circuit having a delay related to the time required for a particle to pass through the COULTER detector orifice. If the comparator signal remains after the delay time, a debris alarm signal is provided. This occurs only if a d.c. voltage shift had occurred, since there is no trailing edge, and hence no undershoot to return the integrated voltage to zero prior to the delay time.

Claims21

Dependent claims

In a particle detector of the type having a small orifice separating two chambers, with a constant current applied through said orifice, and in which particles and debris suspended in a liquid are passed through said small orifice, whereby each particle or debris passing through said orifice causes a voltage pulse across said orifice and debris lodging in or against said orifice causes a d.c. voltage shift across said orifice, and said detector further having sensing means to sense the voltage across said orifice, the improvement of a debris detector comprising:

capacitance means coupling said sensing means to said orifice;
means for integrating the output of said sensing means;
and
means for determining if the integrated sensing means output exceeds a certain value only after a certain delay time.

1 more element

A debris detector for a particle counter of the type in which particles suspended in a fluid pass through a small opening, said opening being coupled in circuit with a constant current source, said counter being constructed to allow the voltage across said opening to be sensed, said fluid further containing debris, some of which can at least partially block said opening and other of which passes through said opening, the resistance of said opening increasing during the time a particle or debris pass therethrough and during the time debris is at least partially blocking said opening, the time for a particle to pass through said opening being less than a certain time, said detector comprising:

amplifying means for providing an amplified version of a voltage applied thereto;
means, including a serially connected capacitor, for coupling the voltage sensed across said opening to said amplifying means, said capacitor maintaining a zero average voltage provided to said amplifying means;
integrating means having an input, to which is applied said amplifying means provided voltage, for providing a voltage which is an integrated version of said amplifying means provided voltage;
and
threshold means, to which said integrating means signal is applied, for providing a debris alarm signal, manifesting the detection of debris at least partially blocking said opening whenever the amplitude of said integrating means voltage remains above a certain threshold amplitude for at least a time related to said certain time.

2 more elements

Dependencies are inferred from the claim text.

Lodged debris detector for a particle analyzer

Life of this patent

Lodged debris detector for a particle analyzer

Life of this patent

Abstract

Claims21