JP3700779B2 - Magnetic oxygen meter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic oximeter that measures, for example, the concentration of oxygen contained in a mixed gas flowing in a flue, and relates to a magnetic oximeter that improves the degree of freedom of controllability of thermomagnetic wind and reduces the influence of ambient temperature fluctuations. About.
[0002]
[Prior art]
Accurate measurement of oxygen concentration in gas mixtures is important in a wide range of industrial, clinical and research processes. For this reason, various apparatuses for measuring the oxygen concentration have been proposed and developed.
[0003]
FIG. 9A shows a configuration of a detection unit of a conventional example of a magnetic oximeter. In the figure, reference numerals 1a and 1b denote magnetic field generating means (permanent magnets) having a predetermined area and magnetic poles arranged to face each other at a predetermined interval. 2a and 2b are thermistors for generating a thermomagnetic wind (hereinafter simply referred to as a magnetic wind), and are disposed in a region (inhomogeneous magnetic field) where the intensity of the magnetic field changes. Reference numerals 3a and 3b denote thermistors (magnetic wind sensors) for detecting the magnetic wind arranged close to the outside of the magnetic wind generating thermistors 2a and 2b.
[0004]
When the magnetic oximeter having the above configuration is arranged in a mixed gas containing oxygen, the oxygen gas, which is a paramagnetic substance, is attracted to the magnetic field by magnetism. When the attracted oxygen gas is heated by the thermistors 2a and 2b that generate heat at the end of the magnetic field, the magnetic susceptibility decreases, and a difference occurs between the magnetic susceptibility of the oxygen gas near the center. As a result, different magnetic forces act on the heated portion and the non-heated portion, and the balance of the forces is lost.
[0005]
There are various arrangements of the magnetic field generating means and the heating element, but the one shown in FIG. 9A is the magnetization of the magnetic field portion where the heating element is not arranged in the region where the strength of the magnetic field changes. Oxygen gas having a high rate is pushed to the heated side of the region where the strength of the magnetic field changes. A gas having a low temperature flows into the region where the intensity of the unheated magnetic field changes, so that a continuous flow occurs.
[0006]
Since the flow of this gas is proportional to the concentration of oxygen gas contained in the mixed gas, the heat of the thermistor (magnetic wind sensor) arranged adjacent to the exothermic thermistor is lowered compared to the exothermic thermistor, and the resistance of the two thermistors The difference in values will be changed.
[0007]
FIG. 9B shows the configuration of FIG. 9A in which the temperature of the oxygen sensing element is controlled to eliminate the influence of fluctuations in the ambient temperature. The resistors Rc, Rd, Rs and the thermistor 2a , 2b, 3a, 3b, Ra, and Rz form a constant temperature bridge. The variable resistor Rt is used for adjusting the bridge temperature, and the amplifier 4 detects when there is an electrical unbalance between the contacts XY, and changes the bridge current to restore the unbalance so that the series transistor 5 can be used. Drive.
[0008]
[Problems to be solved by the invention]
However, in the above-described prior art, the heat generating (winding) thermistor and the magnetic wind sensor are installed in the control circuit so as to be placed at a constant spatial distance and always have a constant resistance value. However, each thermistor is always heated, and the amount of heat generated by the wind-generating thermistor is not always transmitted stably to the magnetic wind sensor.
[0009]
For example, since the direction of natural heat convection due to the heat of the wind-generating thermistor changes due to the change in the attitude of the detector, the amount of heat received by the magnetic wind sensor changes. In addition, the thermal environment of the wind generation and magnetic wind sensor changes due to the change in ambient temperature, and the heat radiation amount of each thermistor changes. Furthermore, temperature fluctuations occur differently at each thermistor installation location.
Due to these phenomena, there has been a problem that the output of the oximeter is greatly fluctuated.
[0010]
For this reason, the detection unit including the thermistor requires strict temperature control, and has a problem that it requires a large and precise thermostat. Further, since direct current detection is performed, there is a problem that the noise band is wide and the S / N is not good.
The present invention has been made to solve such problems, and an object of the present invention is to realize a magnetic oximeter that is highly accurate and has few components without being affected by the posture and temperature drift.
[0011]
[Means for Solving the Problems]
In order to solve such a problem, in claim 1,
Magnetic field generating means for generating a magnetic field from the magnetic poles arranged opposite to each other;
It consists of an AC power supply and all bridges formed by four equivalent heating elements that generate heat when energized and the resistance value changes.
Positions where two opposing heating elements constituting the entire bridge are arranged opposite to a region (inhomogeneous magnetic field) where the intensity of the magnetic field changes, and the other two heating elements are not affected by the magnetic field. And an AC voltage is applied to all the bridges from the AC power supply.
[0012]
In claim 2,
Magnetic field generating means for generating a magnetic field from the magnetic poles arranged opposite to each other;
It consists of an AC power supply and all bridges formed by four equivalent heating elements that generate heat when energized and the resistance value changes.
Two opposing heating elements constituting the entire bridge are arranged opposite to a region (inhomogeneous magnetic field) where the intensity of the magnetic field changes, and the other two heating elements are arranged in the vicinity of the two heating elements. And an AC voltage is applied to all the bridges from the AC power source.
In claim 3,
Magnetic field generating means for generating a magnetic field from the magnetic poles arranged opposite to each other;
It consists of two equivalent heating elements that generate heat when energized and the resistance value changes, and a half bridge formed by two resistors with the same resistance value, and an AC power supply,
The half bridge is connected so that a heating element and a resistor are adjacent to each other, and one of two opposing heating elements is arranged in a region where the intensity of the magnetic field changes (non-uniform magnetic field), and the other heating element Is arranged at a position where the influence of the magnetic field does not reach, and an AC voltage is applied from the AC power source to the opposite connection point.
[0014]
According to a fourth aspect of the present invention, in the magnetic oximeter according to any one of the first to third aspects, the heater drive voltage and the bridge output voltage are divided into a plurality of predetermined time lengths, and output signal processing is performed according to the following equation: It is characterized by that.
Vout = Σ D (t) ・ S (t)
Or
Vout = ∫D (t) ・ S (t) dt
Where D (t): heater drive voltage
S (t): Bridge output voltage
According to a fifth aspect of the present invention, in the magnetic oximeter according to any one of the first to fourth aspects, the heating element is made of tungsten (W), silicon, a silicon compound, or platinum (Pt).
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
First, the measurement principle of the oxygen concentration in the gas containing oxygen used in the conventional example and the present invention will be briefly described with reference to FIGS.
FIG. 7A shows the relationship between oxygen molecules and the magnetic field when the magnetic field generating means is arranged in a gas containing oxygen.
[0017]
Here, the force F in the X-axis direction acting on oxygen molecules can be expressed by the following equation.
F = χ · (∂H / ∂X) · H
χ: oxygen magnetic susceptibility H: magnetic field strength ∂H / ∂X: magnetic field change rate In other words, as shown in FIG. 7B, the magnetic field is strong and its strength changes (the magnetic pole The force attracting oxygen acts on the edge (non-uniform magnetic field), and the right and left forces are balanced against each other at the end of the magnetic pole.
FIG. 7C shows a state in which the attracted oxygen pressure (concentration) is higher in the magnetic field (magnet gap) than in the surrounding area.
[0018]
FIGS. 8A and 8B show a case where a heater is arranged in a region where the intensity of the magnetic field changes (non-uniform magnetic field) and the susceptibility of oxygen is changed. Only the right side is heated to reduce the leftward pressure and pressure. It shows the state that lost the balance.
FIG. 8C shows a state in which the pressure balance is lost, a differential pressure is generated, and a rightward magnetic wind is blowing. This differential pressure (magnetic wind strength) is determined by the oxygen concentration, the magnetic field strength, and the heater heating amount.
[0019]
FIGS. 1A and 1B are main part configuration diagrams of a detection unit showing an example of an embodiment related to claim 1 of the present invention. In FIG. 1 (a), reference numeral 1 denotes a magnetic field applying device having end portions having a predetermined area and spaced apart from each other, and a middle portion (two-dot chain line) of a pair of facing magnetic poles (1a, 1b). It is shown that a uniform magnetic field is formed in the portion (e) indicated by (3), and the end of the magnetic field is a region where the strength of the magnetic field changes (nonuniform magnetic field).
[0020]
FIG. 1B shows all bridges formed by four heating elements (heating filaments, such as W or Pt) having the same performance (the four electronic parts constituting the bridge are the same, and the resistance value changes due to heat generation are the same). The two opposing heating elements (2a, 2c) are arranged in a region where the intensity of the magnetic field changes (non-uniform magnetic field), and the other two opposing heating elements (2b, 2d) ) Is arranged at a position not affected by the magnetic field.
[0021]
Reference numeral 20 denotes an AC power supply of about 10 to 100 Hz, for example. One connection terminal is connected to the connection point of the heating elements 2a and 2d, and the other connection terminal is connected to the connection point of the heating elements 2b and 2c. Output terminals are connected to the connection points of the heating elements 2a and 2b and the connection points of the heating elements 2c and 2d.
[0022]
Even in such a configuration, when placed in a mixed gas containing oxygen, the oxygen gas is attracted to the magnetic field by magnetism, and the attracted oxygen gas is a region where the strength of the magnetic field changes (non-uniform magnetic field). ) Is heated by a heating element arranged in (1). Oxygen with reduced magnetic susceptibility in the vicinity of the heating element due to a difference between the oxygen gas in the region where the intensity of the magnetic field where the magnetic susceptibility has been reduced by heating and the oxygen gas in the non-uniform magnetic field that has not been heated is changed. The gas is pushed away to generate a magnetic wind in the directions of A and B ′ in FIG.
[0023]
In this case, since the applied power source is alternating current, all the heating elements (2a to 2d) are heated at the same time, but the opposing heating elements (2a, 2c) arranged in the non-uniform magnetic field generate magnetic wind, so Only the opposing heating elements (2a, 2c) of all bridges are cooled by the magnetic wind.
As a result, while all the heating elements are heated simultaneously, there is a difference in temperature between 2a, 2c and 2b, 2d. Therefore, an AC bridge output is generated due to the presence of oxygen.
[0024]
2A to 2C show output waveforms depending on the applied voltage and the presence or absence of oxygen. When the AC voltage shown in FIG. 2A is applied, the output when oxygen is present is shown in FIG. The waveform is as shown in FIG. 2C when oxygen is not present.
[0025]
3A to 3C show the relationship between the drive voltage waveform, the output voltage, and the zero-cross detection signal voltage. The period during which the drive voltage is zero-crossed is detected, and the time corresponding to the midpoint of the zero-cross is obtained.
Next, the output voltage at the zero cross point and the output voltage at the mid point between the zero cross point and the zero cross point are obtained and the difference (V−v) is obtained. Since this difference changes in relation to the strength of the magnetic wind, the oxygen concentration can be known.
In this way, even if there is a disturbance that is not related to the oxygen concentration due to a change in posture or an uneven distribution in the ambient temperature, the influence can be reduced.
[0026]
4A to 4C show the output state when the zero point drift occurs, and a large output error occurs in the conventional DC current measurement. In the present invention, the average value and the intermediate point of the output at the zero cross point are shown. Since the output difference (V-v) is detected, only the oxygen signal can be detected without being affected by the fluctuation of the zero point.
[0027]
FIGS. 5A and 5B show another embodiment of the magnetic oximeter of the present invention, which differs from the embodiment shown in FIG. 1B only in the positions of the two heating elements.
That is, as shown in FIG. 5a, two opposing heating elements (2a, 2c) are arranged in a region where the intensity of the magnetic field changes (non-uniform magnetic field), and the other two opposing heating elements (2b, 2d). Are also arranged opposite to each other in the vicinity of the two opposing heating elements (2a, 2c).
FIG. 5B shows the relationship of the temperature of each heating element at the position AA ′ of the heating element when the magnetic oximeter of FIG. 5A is placed in a gas containing oxygen and an alternating current is applied. A curve indicated by a solid line indicates a state where no oxygen is present and no magnetic wind is generated, and a curve indicated by a dotted line indicates a state where a magnetic wind due to oxygen is generated. That is, the dotted curve shows that the heat generating element 2a is cooled by the magnetic wind, and the temperature of the heat generating element 2b disposed downstream thereof rises due to the heat of the heat generating element 2a and the temperature difference (resistance value change) increases. . As a result, the bridge output is larger than that of the embodiment shown in FIG. 1B, and the S / N can be improved.
[0028]
By the way, the above-mentioned oxygen meter uses W, Pt, Si, or Si compound as a heating element, but these heating elements are expensive and are manufactured with the same accuracy or matched with four temperature conditions. There is a problem that is difficult.
[0029]
FIG. 6 shows a case where two opposing heating elements have the same accuracy, for example, a carbon film resistor, a half-bridge (two of the four electronic components constituting the bridge that have the same resistance value change due to heat generation, a simple resistor 2), and only the heating element 2a is arranged in a non-uniform magnetic field. In this case also, the drive voltage waveform, the output voltage waveform, and the zero-cross signal are as shown in FIG. Then, by detecting the difference (V′−v ′) from the output waveform that is output every other point with respect to the midpoint of the zero cross signal, it is possible to detect only the oxygen signal without being affected by the fluctuation of the zero point. it can.
[0030]
According to such a configuration, the sensitivity is halved as compared with the case where four heating elements are used, but the carbon film resistor that is less expensive than the heating element is used as a component of the bridge. Since it is sufficient to produce two products having the above accuracy and match the two temperature conditions, the cost can be reduced as a whole.
[0031]
By the way, the principle of the present invention is as described in FIGS.
When a magnet is disposed in a gas containing oxygen, oxygen is attracted to the non-uniform magnetic field at both ends of the magnet, and the right and left forces are balanced against each other at the ends of the magnetic poles.
Heating oxygen at one end of the oxygen attracted by the non-uniform magnetic fields at both ends changes the susceptibility of the oxygen at that portion, and the pressure balance is lost to generate a differential pressure, thereby generating a magnetic wind.
Since the magnetic wind is proportional to the oxygen concentration, the proportion of oxygen in the gas can be measured. That's it.
[0032]
However, noise due to various disturbances is superimposed on the output, and the output is not necessarily proportional to the oxygen concentration. FIG. 9 shows that the magnetic wind passing through the flow path of the magnetic oximeter causes noise generation due to various factors.
FIG. 10 shows the relationship between the drive waveform (a) and the detected waveform (b) when there is no noise. However, in actuality, it becomes a signal including noise, for example, a waveform as shown in FIG. 11B (in these figures, the mark ● indicates the sampling timing). FIG. 11A shows only the noise component superimposed on the output waveform.
[0033]
Here, as shown in FIG. 11A, the noise amplitude and appearance frequency have a Gaussian distribution as shown in FIG. 11C, and it is known that the average value of noise approaches zero. Here, this is utilized to realize a magnetic oximeter with less noise.
[0034]
FIG. 12 is a flowchart from magnetic wind drive input (filament lighting) to output signal processing. This will be described with reference to the drawings.
B) Magnetic wind drive input D (t) is input.
B) Magnetic wind w (t) is generated.
The generated magnetic wind w (t) is expressed by the following equation.
w (t) = f (H, dH / dX, T, O2, K) · D (t)
Here, f (H, dH / dX, T, O2, K) is a magnetic wind generating ability,
H: magnetic field strength dH / dX; gradient of magnetic field change T; temperature O2; oxygen concentration K; device coefficient, and the sensitivity of the magnetic oximeter is determined by these values.
[0036]
C) The magnetic air volume (w ′ (t)) in the detection unit is detected by the following equation.
w ′ (t) = α · w (t) + ε (t)
Where α: damping coefficient due to pipe resistance (α <1)
ε (t): Disturbance wind (random)
D) The detection signal S (t) is detected by the following equation.
S (t) = k · w ′ (t) = k · α · w (t) + ε (t)
Where k: wind detection coefficient
E) The output Vout (t) as an oximeter is calculated by the following equation.
Vout (t) = ΣD (t) · (k · α · w (t) + k · ε (t))
= K · α · f (H, dH / dX, T, O2, K) ΣD ² (t) + kΣD (t) · ε (t)
Here, the term due to the disturbance of the second term approaches zero due to the randomness of the disturbance as the integration interval becomes longer by integrating or integrating.
as a result,
Vout (t) ≈k · α · f (H, dH / dX, T, O2, K) ΣD ² (t)
Thus, the influence of turbulence can be reduced.
[0038]
As described above, the influence of noise can be reduced by processing the high frequency noise among the output fluctuation factors due to noise using the above-described integration or integration method. That is, it corresponds to adding a high-performance bandpass filter by passing only a very narrow frequency band around the frequency of the drive voltage in the noise spectrum.
Note that although zero bias remains in Vout (t) described above, the actual output is calculated in consideration of that amount.
In the embodiment, the drive voltage waveform is a sine waveform, but may be a rectangular or triangular waveform.
[0039]
The foregoing description of the present invention has only shown certain preferred embodiments for purposes of illustration and illustration. Accordingly, it will be apparent to those skilled in the art that the present invention can be modified and modified in many ways without departing from the essence thereof. The scope of the present invention defined by the description in the appended claims is intended to include modifications and variations within the scope.
[0040]
【The invention's effect】
As described above, according to the present invention, the two opposing heating elements constituting the bridge are arranged to face the non-uniform magnetic field, and the other two heating elements are not affected by the magnetic field. Since the AC voltage was applied to the bridge from the AC power supply,
A magnetic oximeter with high accuracy and few components can be realized without being affected by the posture and temperature drift.
[0041]
In addition, two opposing heating elements constituting the entire bridge are arranged facing a region where the intensity of the magnetic field changes (nonuniform magnetic field), and the other two heating elements are arranged in the vicinity of the two heating elements. Since it is arranged, the output of the bridge is larger than that of the embodiment shown in FIG. 1B, and the S / N can be improved.
[0042]
Further, if two of the components constituting the bridge are made of inexpensive carbon film resistors, the overall cost can be reduced.
[0043]
In addition, by dividing the heater drive voltage and the bridge output voltage into a plurality of predetermined time lengths, multiplying the drive voltage and output, and integrating or integrating the multiplied values, a magnetic oxygen sensor with less noise is obtained. The total can be realized.
[0044]
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an example of an embodiment of a magnetic oximeter according to the present invention.
FIG. 2 is a diagram showing an output waveform depending on the presence or absence of oxygen when an AC voltage is applied.
FIG. 3 is a diagram illustrating a relationship between a drive voltage waveform, an output voltage, and a zero-cross detection signal voltage.
FIG. 4 is a diagram illustrating an output state when a zero point drift occurs.
FIG. 5 is a block diagram showing an example of an embodiment related to claim 2 of the present invention;
FIG. 6 is a block diagram showing an example of an embodiment related to claim 4 of the present invention.
FIG. 7 is an explanatory diagram of the measurement principle of the present invention.
FIG. 8 is an explanatory diagram of the measurement principle of the present invention.
FIG. 9 is an explanatory diagram of the cause of noise generation.
FIG. 10 is a diagram illustrating a relationship between a drive waveform and a detection waveform.
FIG. 11 is an explanatory diagram of noise, a waveform on which noise is superimposed, and a Gaussian distribution of noise.
FIG. 12 is a flowchart from magnetic wind driving input to output signal processing;
FIG. 13 is a diagram illustrating an example of a configuration of a detection unit and a detection circuit of a conventional magnetic oximeter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Magnetic pole 2 (ad) Heating element 2e, 2f Resistor 20 AC power supply

Claims (5)

Magnetic field generating means for generating a magnetic field from the magnetic poles arranged opposite to each other;
It consists of all bridges formed by four equivalent heating elements that generate heat and change resistance as well as an AC power supply.
Positions where two opposing heating elements constituting the entire bridge are arranged opposite to a region (inhomogeneous magnetic field) where the intensity of the magnetic field changes, and the other two heating elements are not affected by the magnetic field. The magnetic oximeter is characterized in that an AC voltage is applied to all the bridges from the AC power source. Magnetic field generating means for generating a magnetic field from the magnetic poles arranged opposite to each other;
It consists of all bridges formed by four equivalent heating elements that generate heat and change resistance as well as an AC power supply.
Two opposing heating elements constituting the entire bridge are arranged opposite to a region (inhomogeneous magnetic field) where the intensity of the magnetic field changes, and the other two heating elements are arranged in the vicinity of the two heating elements. Arranged and applied with an AC voltage from the AC power supply to all the bridges. Magnetic field generating means for generating a magnetic field from the magnetic poles arranged opposite to each other;
It consists of two equivalent heating elements that generate heat when energized and the resistance value changes, and a half bridge formed by two resistors with the same resistance value, and an AC power supply,
The half bridge is connected so that the heating element and the resistor are adjacent to each other, and one of the two opposing heating elements is arranged in a region where the intensity of the magnetic field changes, and the other heating element is influenced by the magnetic field. The magnetic oximeter is arranged at a position where the AC voltage does not reach, and an AC voltage is applied from the AC power source to the opposite connection point. The magnetic oximeter according to any one of claims 1 to 3, wherein the heater drive voltage and the bridge output voltage are divided into a plurality of predetermined time lengths, and output signal processing is performed according to the following equation.
Record
Vout = Σ D (t) ・ S (t)
Or
Vout = ∫D (t) ・ S (t) dt
Where D (t): heater drive voltage
S (t): Bridge output voltage 5. The magnetic oximeter according to claim 1, wherein the heating element is made of tungsten (W), silicon, a silicon compound, or platinum (Pt).

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