JPH09318574A - Metal particle sensor and particle size measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal particle sensor for detecting the metal particle distribution accurately over a wide range of particle size and a particle size measuring method therefor. SOLUTION: The sensor comprises an electrode section 20 having a pair of electrodes to be applied with a predetermined voltage arranged in an insulating medium and pulsating a short circuit current being generated between the electrodes by metal particles mixed in the insulating medium, a signal processing section 30 for detecting the peak voltage of the pulse signal, and a data processing section 40 for calculating the particle size and the concentration of the metal particle in the insulating medium based on the peak voltage value and the count of the pulse signals. The electrode section 20 is provided with a plurality of pairs of electrode of different distance in order to shift the range of particle size to be measured. An interdigital electrode may be employed as the plurality of electrodes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor for measuring the particle size and concentration of conductive particles dispersed in an insulating medium, that is, the particle size distribution.

[0002]

2. Description of the Related Art For example, in a construction machine, an industrial machine or a machine tool, when hydraulic equipment is driven for a long time, metal particles such as iron powder generated from sliding parts and rotating parts of the hydraulic equipment itself are generated. It comes to be mixed in the hydraulic fluid of the hydraulic circuit. Further, when a certain hydraulic device is damaged, iron powder may be mixed into the hydraulic oil. If the iron powder is continuously driven in a state of being mixed in the hydraulic oil, these hydraulic devices are often damaged or malfunction. Similar problems occur with lubricating oils. For example, impurities such as metal particles and carbon generated in the combustion process of an engine are mixed into the lubricating oil, leading to performance deterioration such as engine output reduction, or at worst. Serious failure such as piston damage may occur. In the field of engine technology, there is a great need to detect carbon particles contained in exhaust gas in order to take measures against exhaust gas. Therefore, conventionally, many sensors have been proposed which detect the presence or absence of metal particles such as iron powder mixed in hydraulic oil or lubricating oil and the presence or absence of carbon particles contained in engine exhaust gas.

Further, a metal particle detection sensor has been proposed which detects not only the presence or absence of metal particles such as iron powder as described above, but also the particle size and concentration of the particles, for example, Japanese Patent Laid-Open No. 2-83150. The sensor is described in the publication. 8 to 10 show the metal particle detection sensor described in the publication, which will be described below with reference to the drawings.

FIG. 8 shows a front view of a sensor body of an embodiment according to the publication. The sensor body 10 is composed of a plug having a hexagonal head portion 11 at the upper portion and a tapered screw portion 13 at the lower portion, and can be screwed into a screw hole provided in a side wall of a tube such as a hydraulic pipe. A liquid contact portion surface 15 that is tapered is provided at the lower end of the screw portion 13, and the inside of the sensor body 10 is hollowed from the head portion 11 to the liquid contact portion surface 15 (not shown). ) Is provided. The comb-shaped electrode pair 2 made of platinum foil is exposed and provided inside the surface 15 of the liquid contact portion,
An insulator 3 insulates the comb-shaped electrode pair 2 from the sensor body 10 and the comb-shaped electrodes 2 a and 2 b forming the comb-shaped electrode pair 2. The lead wires 1a of the comb electrodes 2a, 2b,
1b is led to the outside from the head portion 11 through the through hole and is connected to a connector (not shown) or the like, and this connector is connected to a power supply unit or a signal processing unit for measurement. The lead wires 1a and 1b and the sensor body 10 are similarly insulated by the insulator 3.

FIG. 9 shows an example of an electric circuit diagram of the conventional metal particle detection sensor. The comb-shaped electrode pair 2 is formed by arranging comb-shaped electrodes 2a and 2b having a predetermined width D2 and a length L on an insulator with a predetermined electrode-pair distance D1 therebetween, and leads to the comb-shaped electrodes 2a and 2b, respectively. Line 1a,
1b is connected. The lead wire 1b is connected to the ground, and the lead wire 1a is connected to the DC power supply 6 via the resistor 5. The connection point between the resistor 5 and the lead wire 1a is
It is connected to a multi-channel analyzer 9 via a capacitor 7 and an amplifier 8.

The operation of such a configuration will be described with reference to FIG. This figure is an explanatory view of the action when a pulse voltage is generated by the metal particles on the comb electrodes 2a and 2b. When a predetermined DC voltage (for example, DC50V) is applied between the comb electrodes 2a and 2b by the DC power supply 6, the metal particles such as iron powder floating in the oil are ionized and attracted to the electric field between the electrodes, It is adsorbed to the comb-shaped electrode 2b on the cathode side. At this time, since the distance between the adsorbed particles and the comb-shaped electrode 2a becomes short, the electric field between them becomes large, whereby other metal particles floating in the oil are further adsorbed by the particles. In this way, the metal particles are adsorbed in a chain form one after another as shown in FIG. And
As shown in FIG. 10 (2), when a bridge is finally formed between the comb-shaped electrodes 2a and 2b by the chain-shaped metal particles, a large short-circuit current flows through the bridge. This short-circuit current causes a voltage drop across the resistor 5,
The electric potential of the comb-shaped electrode 2a on the positive electrode side decreases. After this, FIG.
As shown in (3), the metal particles forming the bridge scatter due to resistance heat of short-circuit current, discharge, etc., and the electrode state returns to the state before the particle adsorption. As a result, the potential of the positive electrode-side comb-shaped electrode 2a returns to the original potential, so that a pulse voltage is generated. By repeating the above process, a pulse voltage signal appears at the potential of the comb-shaped electrode 2a.

The pulse voltage signal is input to the amplifier 8 by the action of AC coupling by the capacitor 7, amplified to a predetermined voltage level by the amplifier 8 and input to the multi-channel analyzer 9. The multi-channel analyzer 9 measures the peak voltage value of the input pulse signal and at the same time counts the number of input pulse signals.
That is, it has been experimentally confirmed that the peak voltage value of the pulse signal has a correlation with the size of the particle size, and the frequency of occurrence of the pulse signal has a correlation with the concentration of metal particles having a corresponding particle size. Therefore, the corresponding particle size is estimated based on the peak voltage value, and the particle size concentration is estimated from the pulse count number corresponding to this particle size. In this way, the particle size (size) and the concentration (number of particles) of the metal particles mixed in the oil are detected.

[0008]

However, in the metal particle detection sensor as described above, the detection resolution and accuracy of the particle size and concentration of the metal particles to be detected are such that the comb electrodes 2a, 2 are provided.
Since it depends on the electrode pair distance D1 of b, there is a problem that the metal particle distribution of a wide range of particle diameters cannot be detected accurately. That is, in the hydraulic circuit of the same machine, when the particle size of metal particles such as iron powder generated in the hydraulic oil is very uneven depending on the type of hydraulic equipment, and when several kinds of metal particles having this uneven particle size are included. May have a broad particle size distribution. For example, in the hydraulic circuit of construction machinery,
Iron powder of the order of 10 μm is generated mainly from the sliding parts of pumps, cylinders, etc.
It is known that iron powder of about μm is generated. In order to detect this with the same metal particle detection sensor, the electrode pair distance D1 of the comb-shaped electrodes 2a and 2b is, for example, 100 μm.
If it is configured to a certain degree, the detection resolution and accuracy of the metal particles of the order of 10 μm are greatly reduced, and it becomes impossible to measure the smaller particle size accurately. This means that the comb-shaped electrodes 2a,
Since the electrode pair distance D1 of 2b is too large, the probability that metal particles on the order of 10 μm will be in a chain state to form a bridge between the electrodes is extremely small.
It is understood that the peak value of the pulse voltage due to the metal particles of the order of 10 μm becomes extremely small with respect to the metal particles of the order of μm. Therefore, development of a metal particle detection sensor capable of accurately detecting a metal particle distribution in a wide range of particle sizes is strongly desired.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a metal particle detection sensor and a particle size measuring method therefor capable of accurately detecting a metal particle distribution in a wide range of particle sizes. Has an aim.

[0010]

[Means for Solving the Problems, Actions and Effects] In order to achieve the above-mentioned object, it is arranged in an insulating medium, and
An electrode section 20 having an electrode pair to which a predetermined voltage is applied between the electrodes, and pulsed a short-circuit current generated between the electrodes by metal particles mixed in the insulating medium, and an electrode section 20.
Signal processing unit 3 for detecting the peak voltage of the pulse signal from the
0 and the peak voltage from the signal processing unit 30 are input, and the data processing unit 40 that calculates the particle size and concentration of the metal particles in the insulating medium based on the peak voltage value and the count number of the pulse signal. In the metal particle detection sensor provided with, a plurality of electrode pairs having different distances are arranged in the electrode part 20 in order to shift the particle size range to be measured.

According to the first aspect of the present invention, a plurality of electrode pairs are provided, the distances between the electrode pairs are different from each other, and the measurable particle size ranges are shifted from each other. As a result, the particle size in the measurable range corresponding to each electrode pair distance can be accurately measured, and the particle size and concentration of the metal particles can be detected over a wide range of particle sizes by a simple calculation based on the measurement result. it can.

According to a second aspect of the present invention, in the metal particle detection sensor according to the first aspect, the plurality of electrode pairs are
It is composed of a plurality of comb-shaped electrode pairs having different distances.

According to the second aspect of the present invention, the plurality of electrode pairs are comb-shaped electrode pairs, and the electrode pair distances of the comb-shaped electrode pairs are different from each other, and the measurable particle size ranges are shifted from each other. I am configuring. As a result, the particle size in the measurable range corresponding to the electrode pair distance of each comb-shaped electrode pair can be accurately measured, and the particle size and the concentration of the metal particles can be measured over a wide range of particle sizes by a simple calculation based on this measurement result. Can be detected.

According to a third aspect of the present invention, an electrode pair to which a voltage is applied between the electrodes is arranged in an insulating medium, and based on the peak value of the pulse voltage between the electrodes and the pulse count number thereof, In the particle size measuring method of the metal particle detection sensor for measuring the particle size and the concentration of the metal particles mixed in the insulating medium, the particle size range to be measured is widened by a plurality of electrode pairs at different distances.

According to the third aspect of the invention, the electrode pair distances of the plurality of electrode pairs are made different from each other, whereby the measurable particle size ranges are shifted from each other. As a result, the particle size in the measurable range corresponding to each electrode pair distance can be accurately measured, and the particle size and concentration of the metal particles can be detected over a wide range of particle sizes by a simple calculation based on this measurement result. it can.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a basic configuration of a metal particle detection sensor according to the present invention. The electrode unit 20 is composed of one or more electrode pairs, and is disposed in an insulating medium such as hydraulic oil, lubricating oil, or exhaust gas. A short-circuit current flows between the electrodes of the electrode pair due to the metal particles mixed in the insulating medium, and a change in the electrode potential due to the short-circuit current is output to the signal processing unit 30 as a pulse signal. The signal processing unit 30 divides the voltage of the pulse signal, for example, converts the level, performs peak hold of the voltage, and outputs the peak voltage signal to the data processing unit 40. This peak voltage signal is reset for the next peak hold after a predetermined time. The data processing unit 40 performs A / D conversion processing on the input peak voltage signal, and stores the size of the converted peak voltage value and counts up the number of pulses in the peak voltage region corresponding to the size. Then, the above measurement is performed within a predetermined time (for example, 10 minutes), and after the measurement time is over, the particle size is identified based on the magnitude of each of the stored peak voltage values, and the number of pulses is determined. Based on this, processing for identifying the particle concentration is performed.

When the metal particle detection sensor according to the present invention capable of accurately detecting the metal particle distribution in a wide range of particle diameters is constructed according to the above-mentioned basic construction, a combination of the constructions shown in FIG. 2 is possible. FIG. 2 shows that the electrode part 20 has a plurality of electrode pairs 22 having different particle size measurable ranges.
, 22-2, ..., 22-n, and the signal processing unit 30 is provided with the signal processing unit 30 corresponding to each electrode pair 22-1, 22-2 ,. Shown is the case of being configured by 1, 31-2, ... 31-n.

By the combination of such signal processing,
Since it is not necessary to use a plurality of expensive and large metal particle detection sensors, it is possible to configure a practical metal particle detection sensor in terms of cost and size of occupied volume. In this case, the power supply voltage value applied between each electrode pair is
In consideration of the particle size measurable range, the electrode area, the electrode combination, and the like, it is necessary to set the voltage appropriately depending on whether the same voltage is applied or different voltages are applied.

Next, an example of a specific embodiment will be described.
FIG. 3 shows a specific circuit configuration of this embodiment.
The electrode section 20 is provided with a plurality of electrode pairs 22-1, 22-2, ... 22-n (n is a natural number) having mutually different particle size measurable ranges. At this time, the peak voltage values generated in the electrode pairs having adjacent particle size measurable ranges may overlap each other. Also, a plurality of electrode pairs 2
22-1, 22-2, ..., 22-n may be collectively provided on the surface 15 of the liquid contact portion of the plug-shaped sensor body 10 as shown in FIG. 8, or You may arrange | position in the different sensor main body 10, respectively. FIG. 3 shows an example having two electrode pairs 22-1, 22-2 and two signal processing units 31-1, 31-2 corresponding thereto. Electrode pair 22
The positive electrode 22a-1 of -1 is connected to one side of the resistor 25-1, and the other side of the resistor 25-1 is connected to the DC power supply 26. The connection point between the positive electrode 22a-1 and the resistor 25-1 is a capacitor 27-1.
The signal processing unit 31-1 is connected to the data processing unit 31-1 via the.
The positive electrode 22a-2 of the electrode pair 22-2 is connected to one of the resistors 25-2, and the other of the resistors 25-2 is connected to the DC power supply 26. The connection point between the positive electrode 22a-2 and the resistor 25-2 is connected to the signal processing unit 31-2 via the capacitor 27-2, and the output of the signal processing unit 31-2 is connected to the data processing unit 40. ing. The signal processing units 31-1 and 31-2 are composed of, for example, electronic circuits such as operational amplifiers and a microcomputer, and the data processing unit 40 is composed of, for example, a microcomputer.

The DC power supply 26 has a predetermined voltage (for example, DC10).
0V), and the positive electrode 2 via the resistors 25-1 and 25-2.
A voltage is applied to 2a-1 and 22a-2. Resistance 25-1, 25
-2, when short-circuit current flows through the electrode pair 22-1, 22-2, respectively, limits the current value for overcurrent protection and generates a voltage drop proportional to the magnitude of this short-circuit current. Then, a pulse voltage signal is generated. The respective pulse voltage signals are AC-coupled by the capacitors 27-1 and 27-2 and input to the signal processing units 31-1 and 31-2. Further, the signal processing units 31-1 and 31-2 detect the peak value of the pulse voltage signal, and output the peak value to the data processing unit 40. Although one DC power supply 26 is provided in this embodiment, it may be provided for each of the resistors 25-1 and 25-2.

Here, a specific method of constructing the above-mentioned electrode pairs having different particle size measurable ranges will be described.
For example, in hydraulic fluid of a hydraulic circuit of a construction machine, a particle size of 10 μ usually generated in a sliding portion of a hydraulic pump or a hydraulic cylinder.
It is known that the iron powder in the vicinity of m and the iron powder in the rotating portion of the transmission, etc., having a particle diameter in the vicinity of 100 μm have a very large particle diameter concentration. Therefore, it is desired to be able to accurately measure the concentrations in the vicinity of both particle sizes. Generally, an electrode having a small distance between the positive electrode and the negative electrode (hereinafter referred to as an electrode pair distance) can accurately measure a small particle size, and an electrode having a large electrode pair distance can accurately measure a large particle size. Can be measured.

Therefore, the present inventors experimentally obtained an electrode pair distance capable of accurately measuring the concentrations in the vicinity of both particle sizes. The measurable particle size range at this time is shown in FIG. 4, in which the horizontal axis represents the particle size (correlated with the peak value of the pulse voltage) and the vertical axis represents the particle concentration (correlated with the pulse count number). Is represented. In the figure, the particle size range A is measured by an electrode having an electrode pair distance D3 which is optimum for measuring the concentration in the vicinity of a particle size of 10 μm, and the particle size range B is 100 μm.
It is measured by an electrode having an electrode pair distance D4 which is optimum for measuring the concentration in the vicinity of m.

In such a case, the electrode pair distances of the electrode pairs 22-1 and 22-2 in FIG. 3 are made equal to the above electrode pair distances D3 and D4. However, the electrode pair distance D
4 is usually set larger than the electrode pair distance D3, and for example, the electrode pair 22-1, 22-2 or the electrode pair 21-1,
The capacitances of the electrode parts such as 21-2 are made equal. To make the capacitances equal, a capacitor is connected between each electrode pair, or the opposing area of the electrode pair is adjusted.

Then, it becomes possible to measure the particle size of the metal particles and the concentration corresponding thereto by using such an electrode. In the actual measurement, the particle size can be identified by the large correlation between the square of the particle size and the peak value Vp of the generated pulse signal, and the pulse for each particle size (that is, for each peak value Vp) can be identified. Since the signal generation frequency (that is, the number of counts) and the concentration are highly correlated, the concentration for each particle size can be identified. Based on the measured data thus obtained, a particle size distribution as shown in FIG. 5 is created. In order to facilitate the creation of this particle size distribution, the data processing unit 40 divides the peak voltage value on the horizontal axis into predetermined voltage widths and counts the pulses included in each voltage width, as shown in FIG. We have created a diagram with numbers on the vertical axis. In the figure, each voltage division on the horizontal axis is represented by Vi, and the count number corresponding to each voltage division Vi is represented by Ci (V). The voltage classification V
If the number of divisions of i is increased, the accuracy of the particle size distribution is improved, but the computer processing time of the data processing unit 40 is increased. Therefore, it is necessary to set the number of divisions in relation to the computing ability of the computer.

Next, the flow of creating the particle size distribution with the above configuration will be described with reference to FIG. FIG. 7 shows an example of a processing flowchart performed by the data processing unit 40, and here, each step number is represented by adding S. In S1 to S4 below, the peak voltage signals output from the signal processing units 31-1 and 31-2 are individually input, and the electrode pairs 22-1 and 22-2 are input based on the peak value Vp of each peak voltage signal.
The particle size distribution corresponding to -2 (that is, voltage distribution Vi of peak voltage and count number Ci (V)) is obtained. Each step will be described in detail. In S1, the timer value T and the count number Ci (V) are reset. Where timer value T
Is a variable for measuring the data measurement time for creating the particle size distribution as described above, and Ci (V) is the count number corresponding to each voltage division Vi of this particle size distribution. Immediately before proceeding to S2, counting of the timer value T is started. Next, in S2, the peak value Vp of the pulse voltage signal is input from the signal processing unit 30, and in S3, the count number Ci (V) corresponding to the voltage section Vi including the input peak value Vp is incremented by one. . Then, in S4,
Enter the timer value T, and the timer value T is the measurement unit time T.
It is determined whether or not it has become 0 or more. This measurement unit time T
0 is a unit time for collecting data for creating the particle size distribution, and is set in advance to a predetermined value, for example, 10 minutes.
If the timer value T is not equal to or more than the measurement unit time T0 in S4, the process returns to S2 and the process is repeated, and the timer value T
Is greater than the measurement unit time T0, the process proceeds to S5.

In step S5, the electrode pairs 22-1, 22-1 and 22-2 are collected on the basis of the voltage classification Vi and the count number Ci (V) data for each electrode pair 22-1, 22-2 collected within the measurement unit time T0.
Create a particle size distribution (particle size classification Ri and concentration) for each 22-2. Further, the concentrations of the respective grain size distributions are summed up for each grain size category Ri to calculate the total concentration. Here, each electrode pair 22-1, 22
The density of the particle size distribution for each −2 is calculated by multiplying the count number Ci (V) by the conversion factors α1 and α2 (occurrence frequency function). The conversion coefficients α 1 and α 2 (occurrence frequency function) are functions of the electrode pair distance, the electrode area (area of the electrode pair), the flow velocity of the measuring medium, etc., and the count number Ci (V) and the particle concentration are determined by their sizes. This is to correct the difference in the proportional coefficient between and. That is, in the present embodiment, the count number Ci (V) at each electrode pair 22-1, 22-2 is multiplied by the conversion coefficients α1, α2 corresponding to the distance between each electrode pair to obtain the concentration M1i,
Find M2i. Further, the particle size classification Ri corresponding to each voltage distribution Vi in each electrode pair 22-1, 22-2 is obtained. With these, a particle size distribution is created for each of the electrode pairs 22-1, 22-2. Then, for each of the same particle size classification Ri, each electrode pair 22-
The concentrations of the particle size distributions of 1 and 22-2 are summed up, and the sum is used as the concentration of the entire particle size distribution. This calculates the particle concentration over a wide range of particle sizes.

As described above, since the electrode portion 20 provided with a plurality of electrodes having mutually different particle size measurable ranges is provided, the particle size and concentration of the metal particles in the insulating medium can be varied over a wide range of particle sizes. It enables accurate measurement. At this time, since only a plurality of electrodes are provided at the tip portion of the sensor body 10, the installation place of the present metal particle detection sensor does not become large, and it can be realized at a low cost. It should be noted that, although the electrode pair is configured by a comb-shaped electrode pair in the drawings described so far, the present invention is not limited to this, and may be configured by an electrode pair in which flat electrodes are opposed to each other, for example. . At this time, an electrode unit 20 including a plurality of flat plate electrode pairs or a plurality of electrodes set to electrode pair distances corresponding to different particle size measurable ranges
And The action and effect at this time are similar to the above.

[Brief description of drawings]

FIG. 1 shows a basic configuration of a metal particle detection sensor according to the present invention.

FIG. 2 is a block diagram showing the configuration of a metal particle detection sensor according to the present invention.

FIG. 3 shows a configuration example of an embodiment of a metal particle detection sensor according to the present invention.

FIG. 4 is an explanatory diagram of different measurable particle size ranges of the metal particle detection sensor according to the present invention.

FIG. 5 is an example of a particle size distribution created by the metal particle detection sensor according to the present invention.

FIG. 6 is an explanatory diagram of creating a particle size distribution by the metal particle detection sensor according to the present invention.

FIG. 7 shows an example of a flow chart for creating a particle size distribution according to the present invention.

FIG. 8 is a front view of an example of a sensor body of a metal particle detection sensor according to a conventional technique.

FIG. 9 shows an example of an electric circuit diagram of a metal particle detection sensor according to a conventional technique.

FIG. 10 is a diagram for explaining the operation when a pulse voltage is generated at the electrode according to the conventional technique.

[Explanation of symbols]

1a, 1b ... Lead wires, 2 ... Comb-shaped electrode pairs, 2a, 2b ...
Comb-shaped electrodes, 3 ... Insulator, 5 ... Resistor, 6 ... DC power supply, 7 ...
Capacitor, 8 ... Amplifier, 9 ... Multi-channel analyzer, 10 ... Sensor body, 11 ... Head, 13 ... Screw part,
15 ... Liquid contact part surface, 20 ... Electrode part, 22-1, 22-
2, 22-n ... Electrode pair, 22a-1, 22a-2 ... Positive electrode, 2
5 ... Resistance, 26 ... DC power supply, 27 ... Capacitor, 30 ...
Signal processing unit, 31-1, 31-2, 31-n ... Signal processing unit, 4
0 ... Data processing unit, A, B ... Particle size range, Vp ... Peak voltage value, Vi ... Voltage classification, Ci (V) ... Count number.

Claims (3)

[Claims] 1. A short-circuit current generated between the electrodes by an electrode pair disposed in an insulating medium and having a predetermined voltage applied between the electrodes, the metal particles mixed in the insulating medium. An electrode section (20) for pulsing the, and a signal processing section (30) for detecting the peak voltage of the pulse signal from the electrode section (20),
A peak voltage from the signal processing unit (30) is input, and based on the peak voltage value and the count number of the pulse signal, a data processing unit (40) for calculating the particle size and the concentration of the metal particles in the insulating medium. In the metal particle detection sensor provided with, in the electrode part (20), in order to shift the particle size range to be measured,
A metal particle detection sensor characterized in that a plurality of electrode pairs having different distances are arranged. 2. The metal particle detection sensor according to claim 1, wherein the plurality of electrode pairs are a plurality of comb-shaped electrode pairs having different distances. 3. An electrode pair to which a voltage is applied between the electrodes is arranged in an insulating medium, and the electrodes are mixed in the insulating medium based on the peak value of the pulse voltage between the electrodes and the pulse count number thereof. A particle size measuring method of a metal particle detecting sensor for measuring the particle size and concentration of metal particles, characterized in that a wide range of particle size is measured by a plurality of electrode pairs at different distances. Particle size measurement method.