Electrical sensing system for measuring ferrous particles within a fluid with temperature compensation circuit

• US 4,878,019 A
• Filed: 08/31/1987
• Issued: 10/31/1989
• Est. Priority Date: 05/02/1985
• Status: Expired due to Term

• Current Assignee: Vickers Incorporated (Eaton Corporation PLC.)
• Original Assignee: Aeroquip Corporation (Eaton Corporation PLC.)
• Inventors: Maris, Nicholas P., Montague, Charles, Tsaprazis, Edward
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US07/091,576
• Time in Patent Office: 792 Days
• Field of Search: 324/204, 324/225, 324/232-234, 324/236, 324/237, 324/327, 324/59, 340/631, 331/65
• US Class Current: 324/204
• CPC Class Codes: F16N 29/00 Special means in lubricating arrangements or systems providing for the indication or detection of undesired conditions; Use of devices responsive to conditions in lubricating arrangements or systems
• CPC Class Codes: G01N 15/0656 using electric, e.g. electrostatic methods or magnetic methods by investigating individual particles G01N15/1031, G01N15/12
• CPC Class Codes: G01N 27/74 of fluids G01N24/00 takes precedence
• CPC Class Codes: G01N 33/2858 metal particles

Abstract

A magnetic sensor for the collection and measurement of ferrous particles through the use of an electronic tuned circuit is disclosed. The sensor contains an electrical inductance along with an integral magnet to attract ferrous particles suspended in the fluid. The ferrous particles collecting on the magnetic surface of the sensor causes a change in the inductance of the integral coil which is measured by an electronic circuit. The electronic circuit operating in conjunction with the sensor utilizes a parallel tuned resonant circuit and time variant frequency multiplying to eliminate undesired response changes of the tuned circuit due to the temperature change of the sensor. The sensor may be located in environmental conditions which include a large variation in ambient temperature. The disclosed invention provides for compensation of such undesired changes caused by temperature change so that the actual change of the inductance in the sensor can be monitored without interference. The signal output from the circuit disclosed is representative of the amount of ferrous debris accumulated on said sensor.

Claims

1. A means for sensing ferrous contamination in a fluid comprising:

(a) a generally cylindrical magnet;

(b) an electrical coil located co-axially on one end of said magnet, said coil having a hole lengthwise through its center;

(c) a pole piece of said magnet occupying the hole in said first coil and concentric with said magnet disposed at one end of the magnet, said pole piece of the magnet being available to accumulate ferrous contamination present in a fluid whereby any ferrous accumulation changes the induction of the coil;

(d) An electronic circuit means for measuring inductance changes of said electrical coil including;

a clock oscillator means providing two discrete frequencies, one high frequency and one low frequency;

a frequency selection means to select, upon command, one of the two frequencies of the said clock oscillator means;

a waveform generator;

a waveform period counter which switches between one of two states corresponding to said high frequency and said low frequency of said clock oscillator;

a sample and hold counter control means operatively connected to said waveform period counter;

a first sample and hold amplifier;

a second sample and hold amplifier;

a constant current coil driver circuit driving a tuned circuit having a resonant frequency between said high frequency and said low frequency, said tuned circuit including said electrical coil;

a first differential amplifier; and

a second differential amplifier;

wherein said clock oscillator is operatively connected to the frequency selection means, and said frequency selection means alternatively selects said high and low frequency from said oscillator means to introduce such frequency into the waveform generator, said waveform generator producing a frequency output proportional to the said selected high or low frequency and introducing said proportional output to the said coil driver constant current circuit, and the said waveform period counter;

wherein further said constant current driver provides a constant current to said tuned circuit, the output of said tuned circuit being placed across the input of said first differential amplifier such that the output of said amplifier represents the voltage across said tuned circuit;

the output of said amplifier being introduced to the input of said first and second sample and hold amplifiers, said first sample and hold amplifier driving an inverting input of said second differential amplifier and said second sample and hold amplifier driving a non-inverting input of said second differential amplifier said second differential amplifier providing an output proportional to inductance changes of said electrical coil;

wherein further said first and second sample and hold amplifiers are commanded through said sample and hold counter control means to sample and hold by said waveform period counter in a manner corresponding to said high frequency and said low frequency of said clock oscillator means.

2. The means for sensing ferrous contamination in a fluid as in claim 1 further comprising an adjustable voltage source and a third differential amplifier with the non-inverting input of said third amplifier operatively connected to the output of the second differential amplifier and said adjustable voltage source is connected to the inverting input of said third differential amplifier.

3. The means for sensing ferrous contamination in a fluid as in claim 2 further wherein the output of said third differential amplifier is operatively connected to a further stage of amplification which provides low-pass filtering.