Electrical sensing circuitry for particle analyzing device
First Claim
1. Electrical sensing circuitry for a particleanalyzing device wherein liquid containing particles is caused to flow through a sensing aperture on either side of which is located a sensing electrode, said circuitry being independent of slow changes in aperture diameter and including constant voltage means coupled to said electrodes for establishing an electric excitation current through said aperture and means coupled to said electrodes for detecting signals generated by particles passing through said aperture, said means for establishing an electric excitation current through said aperture having a low output impedance at D.C.and said means coupled to said sensing electrodes for detecting signals generated by particles passing through said aperture having a low input impedance at the frequencies of the particle-generated signals, said circuitry including circuit means for coupling said signal-detecting means, said electrical excitation current establishing means, and the voltage potential across said aperture in such a manner that the D.C. component of the excitation current flowing through said aperture is made to vary inversely proportional to slow changes of the steady state resistance of the resistance across said sensing electrodes through said aperture with voltage across said sensing electrodes remaining constant.
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Abstract
The electrical sensing circuitry includes a power supply and a signal-detecting circuit which are coupled through the resistance of an electrolyte in a liquid in an aperture of a particle-analyzing device between sensing electrodes positioned on either side of the aperture. The liquid containing an electrolyte and the passage of a liquidborne particle through the aperture causes a change in the resistance of the aperture thereby generating a signal which is detected by the signal-detecting circuit. The parameters of the circuit elements are chosen to provide circuit relationships which render the particle-generated signal independent of the diameter of the aperture. This is achieved by utilizing a power source having a low output impedance and a signal-detecting circuit which has a low input impedance for both D.C. and A.C., namely, at the signal frequencies of the signals sensed. The electrical circuitry also may include a conductivity monitoring circuit which may utilize one or more of the sensing electrodes and/or additional electrodes for monitoring changes in conductivity of the electrolyte and for relating these changes in conductivity to the particle-generated signals sensed by the signal-detecting circuit to alter those signals so as to render them independent of electrolyte resistivity.
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Citations
30 Claims
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1. Electrical sensing circuitry for a particleanalyzing device wherein liquid containing particles is caused to flow through a sensing aperture on either side of which is located a sensing electrode, said circuitry being independent of slow changes in aperture diameter and including constant voltage means coupled to said electrodes for establishing an electric excitation current through said aperture and means coupled to said electrodes for detecting signals generated by particles passing through said aperture, said means for establishing an electric excitation current through said aperture having a low output impedance at D.C.
and said means coupled to said sensing electrodes for detecting signals generated by particles passing through said aperture having a low input impedance at the frequencies of the particle-generated signals, said circuitry including circuit means for coupling said signal-detecting means, said electrical excitation current establishing means, and the voltage potential across said aperture in such a manner that the D.C. component of the excitation current flowing through said aperture is made to vary inversely proportional to slow changes of the steady state resistance of the resistance across said sensing electrodes through said aperture with voltage across said sensing electrodes remaining constant.
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19. Electrical sensing circuitry for a particle-analyzing device wherein liquid containing particles is caused to flow through a sensing aperture on either side of which is located a sensing electrode, said circuitry including means coupled to said electrodes for establishing an electric excitation current through said aperture, means coupled to said electrodes for detecting signals generated by particles passing through said aperture and electrical monitoring means coupled to said signal-detecting means for monitoring the conductivity of the liquid containing particles and for electrically altering the output signals from said signaldetecting means relative to changes in the liquid conductivity, said circuitry including a modulator, the output of said signal detecting means being connected to said modulator which superimposes the output signals on a carrier frequency, said modulator having a current output stage coupled to a demodulator, and said conductivity monitoring means including a pair of conductivity sensing electrodes forming a conductivity cell in the liquid containing particles, said conductivity cell being connected to the input of said demodulator whereby the particle-generated signals on the carrier frequency at the input to the demodulator are simultaneously applied to a load resistance dependent upon conductivity of the liquid so that the output signals from said demodulator are independent of liquid conductivity.
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20. Electrical sensing circuitry for a particle-analyzing device wherein liquid containing particles is caused to flow through a sensing aperture on either side of which is located a sensing electrode, said circuitry including means coupled to said electrodes for establishing an electric excitation current through said aperture, means coupled to said electrodes for detecting signals generated by particles passing through said aperture and electrical monitoring means coupled to said signal-detecting means for monitoring the conductivity of the liquid containing particles and for electrically altering the output signals from said signaldetecting means relative to changes in the liquid conductivity thereby to render said output signals independent of liquid conductivity, said circuitry further including a modulator, the output of said signaldetecting means being connected to said modulator which superimposes said output signals on a carrier frequency, said modulator having a current output stage coupled to the input of a demodulator through the primary of a transformer and an inductance, a capacitor being connected between said demodulator input and the common conductor for said circuitry, and said conductivity monitoring means including a conductivity cell defined by two electrodes situated in the liquid in which one of said sensing electrodes is situated, said conductivity cell being connected across the secondary of said transformer.
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21. Electrical sensing circuitry for a particle-analyzing device wherein liquid containing particles is caused to flow through a sensing aperture on either side of which is located a sensing electrode, said circuitry including means coupled to said electrodes for establishing an electric excitation current through said aperture, means coupled to said electrodes for detecting signals generated by particles passing through said aperture and electrical monitoring means coupled to said signal-detecting means for monitoring the conductivity of the liquid containing particles and for electrically altering the output signals from said signaldetecting means relative to changes in the liquid conductivity thereby to render said output signals independent of liquid conductivity, and wherein said signal-detecting means includes an amplifier, and a first capacitance and a first resistance connected across said electrodes, the junction between said first capacitance and said first resistance being connected to the input of said amplifier, and said conductivity monitoring means including said sensing electrodes, a second resistance and a second capacitance connected across said sensing electrodes, and a divider for coupling said conductivity monitoring means to said signal-detecting means, the output of said amplifier being connected to the numerator input of said divider and the junction between said second resistance and said second capacitance being connected to the denominator input of said divider.
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22. Electrical sensing circuitry for a particleanalyzing device wherein liquid containing particles is caused to flow through a sensing aperture on either side of which is located a sensing electrode, said circuitry including means coupled to said electrodes for establishing an electric excitation current through said aperture, means coupled to said electrodes for detecting signals generated by particles passing through said aperture and electrical monitoring means coupled to said signal-detecting means for monitoring the conductivity of the liquid containing particles and for electrically altering the output signals from said signaldetecting means relative to changes in the liquid conductivity thereby to render said output signals independent of liquid conductivity, and wherein said signal-detecting circuit includes a capacitor and a resistance connected across said electrodes and an amplifier connected to the junction between said capacitor and resistance, and said conductivity monitoring means includes said sensing electrodes, an oscillator and a capacitor connected in series across said electrodes, a capacitance and a inductance series tuned to the frequency of said oscillator and connected between the output of said amplifier and the common conductor for said circuitry, and a divider for coupling said conductivity monitoring means to said signal-detecting means, the junction between said capacitance and inductance being connected through a phase-sensitive filter to the denominator input of said divider and the output of said amplifier being connected to the numerator input of said divider.
- 23. Electrical sensing circuitry for a particle-analyzing device wherein liquid containing particles is caused to flow through a sensing aperture on either side of which is located a sensing electrode, said circuitry including means coupled to said electrodes for establishing an electric excitation current through said aperture, means coupled to said electrodes for detecting signals generated by particles passing through said aperture and electrical monitoring means coupled to said signal-detecting means for monitoring the conductivity of the liquid containing particles and for electrically altering the output signals from said signal-detecting means relative to changes in the liquid conductivity thereby to render said output signals independent of liquid conductivity, said means for monitoring conductivity including a conductivity cell defined by a pair of conductivity sensing electrodes in the liquid, said conductivity cell forming a resistance which is connected as a load resistance to the output of said signal-detecting means, and wherein said conductivity cell is physically isolated from the sensing zone including said sensing aperture.
- 27. In a particle study device wherein a liquid electrolyte containing particles is caused to traverse an electrical sensing zone of small dimensions and wherein said device has a conductivity cell including two electrodes in the electrolyte for establishing a variable resistance which is the function of the conductivity of the electrolyte and which is connected to electrical sensing circuit including the sensing zone to provide compensation for changes in electrolyte conductivity, the improvement comprising said conductivity cell including a long and narrow column of electrolyte between said electrodes with each of said electrodes being in contact with the electrolyte at one end of said column.
Specification