JP2002039998A - Magnetic oximeter - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a magnetic oximeter with high accuracy and few components, which is not affected by posture and temperature drift. SOLUTION: The magnetic field generating means generates a magnetic field from magnetic poles arranged opposite to each other, all bridges formed by four equivalent heating elements which generate heat and change the resistance value when energized, and an AC power supply. The two opposing heating elements constituting the entire bridge are arranged opposite to the area where the magnetic field intensity changes (non-uniform magnetic field), and the other two opposing heating elements are arranged at positions where the magnetic field does not affect. An AC voltage was applied to all the bridges from an AC power supply. In addition, two opposite heating elements constituting the entire bridge are arranged to face a region where the magnetic field intensity changes (non-uniform magnetic field), and the other two opposite heating elements are arranged near the two heating elements. did.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic oximeter for measuring, for example, the concentration of oxygen contained in a gas mixture flowing in a flue, and to improve the controllability of thermomagnetic wind and the influence of ambient temperature fluctuation. The present invention relates to a magnetic oximeter with reduced oximetry.

[0001]

2. Description of the Related Art Accurate measurement of the oxygen concentration in a mixed gas requires
Important in a wide range of industrial, clinical and research processes. For this reason, various devices for measuring the oxygen concentration have been proposed and developed.

FIG. 9 (a) shows the configuration of a conventional detection unit of a magnetic oximeter. In the figure, reference numerals 1a and 1b denote magnetic field generating means (permanent magnets) having a predetermined area and having magnetic poles arranged facing each other at a predetermined interval. Reference numerals 2a and 2b denote thermistors for generating a thermomagnetic wind (hereinafter, simply referred to as a magnetic wind), which are arranged in a region where the intensity of the magnetic field changes (non-uniform magnetic field). 3a and 3b are magnetic wind generation thermistors 2a and 2
This is a thermistor (magnetic wind sensor) that detects a magnetic wind disposed close to the outside of b.

When the magnetic oximeter having the above structure is arranged in a mixed gas containing oxygen, the magnetism attracts the paramagnetic oxygen gas to the magnetic field. When the attracted oxygen gas is heated by the thermistors 2a and 2b that generate heat at the ends of the magnetic field, the magnetic susceptibility decreases, and a difference is generated between the oxygen gas and the magnetic susceptibility near the center. As a result, different magnetic forces act on the heated part and the non-heated part, and the balance of the forces is lost.

There are various structures in the arrangement of the magnetic field generating means and the heating element, and the arrangement shown in FIG. 9A is a magnetic field in which the heating element is not disposed in a region where the intensity of the magnetic field changes. Oxygen gas having a high magnetic susceptibility in a portion will be pushed to the heated side of the region where the intensity of the magnetic field changes. Since a low-temperature gas flows into a region where the strength of the unheated magnetic field changes, a continuous flow occurs.

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 heat generating thermistor is reduced as compared with the heat generating thermistor, and The difference in the resistance value of the thermistor will be changed.

FIG. 9 (b) shows the configuration of FIG. 9 (a).
By controlling the temperature of the oxygen sensing element, the influence of the fluctuation of the ambient temperature is removed.
Rd, Rs and thermistors 2a, 2b, 3a, 3b, R
The bridge for constant temperature is formed by the bridge composed of a and Rz. The variable resistor Rt is used for adjusting the bridge temperature, and the amplifier 4 detects when there is an electrical imbalance between the contacts XY, and changes the bridge current to recover the imbalance by changing the bridge current.
Drive.

[0007]

However, in the above-mentioned prior art, the control circuit is arranged so that the heat-generating (blowing) thermistor and the magnetic wind sensor are placed at a spatially constant distance and always have a constant resistance value. Built in. But,
Each thermistor is constantly heated, and the amount of heat of the blowing thermistor is not always transmitted to the magnetic wind sensor stably.

For example, the direction of natural heat convection due to the heat of the blowing thermistor changes due to a change in the attitude of the detector, so that the amount of heat received by the magnetic wind sensor changes. Also,
Due to the change in the ambient temperature, the thermal environment of the blast and the magnetic wind sensor changes, and the heat radiation amount of each thermistor changes. Furthermore, temperature fluctuations occur differently for each thermistor installation location. There was a problem that the output of the oxygen meter was greatly fluctuated by these phenomena.

For this reason, there has been a problem that the detecting section including the thermistor requires strict temperature control and requires a large-scale and precise thermostat. In addition, since DC detection is performed, there is a problem that a noise band is wide and S / N is not good. The present invention has been made to solve such a problem, and an object of the present invention is to realize a magnetic oximeter which is not affected by posture and temperature drift and has high accuracy and few components.

[0010]

In order to solve the above-mentioned problems, a first aspect of the present invention is a magnetic field generating means for generating a magnetic field from magnetic poles disposed opposite to each other, a magnetic field generating means which generates heat when energized and has a resistance value. And an AC power supply, and oppose two opposite heating elements constituting the all bridge to a region (non-uniform magnetic field) where the intensity of the magnetic field changes. The other two heating elements are arranged at positions where the influence of the magnetic field does not affect, and an AC voltage is applied to all the bridges from the AC power supply.

According to a second aspect of the present invention, there is provided a magnetic field generating means for generating a magnetic field from magnetic poles disposed opposite to each other, and all bridges formed by four equivalent heating elements which generate heat when energized and whose resistance value changes, An AC power supply, two opposed heating elements constituting the entire bridge are arranged facing a region (non-uniform magnetic field) where the intensity of the magnetic field changes, and the other two opposed heating elements are connected to the two heating elements. It is arranged near a heating element, and an AC voltage is applied from the AC power supply to all the bridges.

According to a third aspect, in the magnetic oximeter according to the first or second aspect, the heating element is made of tungsten (W), silicon, a silicon compound, or platinum (Pt).

According to a fourth aspect of the present invention, there is provided a magnetic field generating means for generating a magnetic field from magnetic poles disposed opposite to each other, two equal heating elements which generate heat when energized and change their resistance values, and two equal heating elements each having the same resistance value. A half-bridge formed of a resistor and an AC power supply. The half-bridge is connected so that the heating element and the resistor are adjacent to each other, and changes the strength of the magnetic field in one of two opposing heating elements. In an area (non-uniform magnetic field), and the other heating element is arranged at a position where the influence of the magnetic field does not affect, and an AC voltage is applied from the AC power source to the opposite connection point.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. First, the principle of measuring 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 a magnetic field when the magnetic field generating means is arranged in a gas containing oxygen.

Here, the force F acting on the oxygen molecules in the X-axis direction can be expressed by the following equation. F = χ · (∂H / ∂X) · Hχ: magnetic susceptibility of oxygen H: strength of magnetic field ∂H / ∂X: rate of change of magnetic field In other words, as shown in FIG. In addition, a force that attracts oxygen acts where the strength is changing (the end of the magnetic pole: an inhomogeneous magnetic field), and the rightward and leftward forces are pressed and balanced at the end of the magnetic pole. . FIG.
(C) shows a state in which the pressure (concentration) of the attracted oxygen is higher in the magnetic field (gap of the magnet) than in the surroundings.

FIGS. 8A and 8B show a case where a heater is disposed in a region where the magnetic field intensity changes (non-uniform magnetic field) to change the magnetic susceptibility of oxygen. Only the right side is heated to reduce the leftward pressure. This shows a state in which the balance of the pressure is weakened and the pressure is lost. FIG.
(C) shows a state in which the pressure balance is lost and a differential pressure is generated, and a rightward magnetic wind is blowing. This pressure difference (the strength of the magnetic wind) is determined by the oxygen concentration, the strength of the magnetic field, and the heating amount of the heater.

FIGS. 1A and 1B are main part configuration diagrams of a detection section showing an example of an embodiment according to claim 1 of the present invention. In FIG. 1 (a), reference numeral 1 denotes a magnetic field applying device whose ends have a predetermined area and are arranged at a predetermined interval, and are located in the middle of a pair of opposed magnetic poles (1a, 1b) (two-dot chain line). This indicates that a uniform magnetic field is formed in the area (e) indicated by the arrow, and the end of the magnetic field is a region where the intensity of the magnetic field changes (non-uniform magnetic field).

FIG. 1 (b) shows a resistance change due to heat generation in which all bridges formed by four heating elements (heating filament... W or Pt, etc.) having the same performance are equivalent. Are equivalent), and the two opposing heating elements (2a, 2c)
Are arranged in a region where the strength of the magnetic field changes (non-uniform magnetic field), and the other two opposite heating elements (2b, 2d) are arranged at positions where the influence of the magnetic field does not affect.

Reference numeral 20 denotes an AC power supply of, for example, about 10 to 100 Hz. One connection terminal is connected to a connection point of the heating elements 2a and 2d, and the other connection terminal is connected to the heating elements 2b and 2c.
Connected to the connection point. The heating elements 2a, 2b
The output terminal is connected to the connection point of the heating element 2c and 2d.

Even in such a configuration, when arranged in a mixed gas containing oxygen, the oxygen gas is attracted to the magnetic field by magnetism according to the same principle as described above, and the attracted oxygen gas is applied to a region where the strength of the magnetic field changes ( It is heated by a heating element arranged in a non-uniform magnetic field. There is a difference between the susceptibility of the oxygen gas in the region where the intensity of the magnetic field whose magnetic susceptibility has been reduced by heating changes and the oxygen gas of the non-uniform magnetic field that has not been heated, and the oxygen whose magnetic susceptibility has decreased near the heating element The gas is pushed away and a magnetic wind is generated in the directions of A and A ′ in FIG. 1 (b).

In this case, since the applied power is AC, all the heating elements (2a to 2d) are heated at the same time, but the opposite heating elements (2a, 2c) arranged in the non-uniform magnetic field generate magnetic wind, so that Only the opposing heating elements (2a, 2c) of all the opposing bridges are cooled by the magnetic wind. As a result, there is a difference in temperature between 2a, 2c and 2b, 2d while all the heating elements are heated simultaneously.
Therefore, an AC bridge output is generated due to the presence of oxygen.

FIGS. 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 in the presence of oxygen is shown in FIG. )
In the case where oxygen does not exist, the waveform becomes as shown in FIG.
The waveform is as shown in FIG.

FIGS. 3A to 3C show the relationship between the drive voltage waveform, the output voltage, and the zero-cross detection signal voltage. A period in which the drive voltage crosses zero is detected, and a 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 zero-cross point and the middle point of 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 a disturbance that is unrelated to the oxygen concentration due to a change in posture or an uneven distribution in the ambient temperature occurs, the effect can be reduced.

FIGS. 4A to 4C show an output state when a zero point drift occurs. In the conventional DC current measurement, a large output error occurs, but in the present invention, the average value of the output at the zero cross point is shown. Since the difference (V−v) between the output and the intermediate point is detected, only the oxygen signal can be detected without being affected by the fluctuation of the zero point.

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, FIG.
a, two opposing heating elements (2a, 2a
c) is arranged in a region where the strength of the magnetic field changes (non-uniform magnetic field), and the other two opposite heating elements (2b, 2d) also face each other near the two opposite heating elements (2a, 2c). It is arranged. FIG. 5 (b) is the same as FIG.
Shows the relationship between the temperature of each heating element at the position of AA ′ of the heating element when an alternating current is applied while the magnetic oximeter is placed in a gas containing oxygen. Indicates a state where no magnetic wind is generated and no dotted line indicates a state where a magnetic wind due to oxygen is generated. That is, the dotted curve indicates the heating element 2a due to the magnetic wind.
Is cooled, and the temperature of the heating element 2b disposed downstream thereof increases due to the influence of the heat of the heating element 2a, and the temperature difference (change in resistance value) increases. As a result, the output of the bridge is larger than that of the embodiment shown in FIG. 1B, and the S / N can be improved.

By the way, the above-mentioned oximeter uses W, Pt, Si, and Si compounds as heating elements, but these heating elements are expensive and can be manufactured with the same accuracy or have four temperature conditions. There is a problem that it is difficult to match.

FIG. 6 shows two opposite heating elements having the same accuracy, for example, a half bridge as a carbon film resistor. Only two resistors are used), and only the heating element 2a is arranged in a non-uniform magnetic field. In this case as well, 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 ') between the middle point of the zero-cross signal and the output waveform output every other point, it is possible to detect only the oxygen signal without being affected by the fluctuation of the zero point. it can.

According to such a configuration, the sensitivity is reduced to half as compared with the case where four heating elements are used, but a carbon film resistor which is less expensive than the heating elements is used as a component of the bridge. Therefore, two devices having the same accuracy may be manufactured and the two temperature conditions may be matched, so that the overall cost can be reduced. The drive voltage waveform is a sine waveform, but may be a rectangular or triangular waveform.

The foregoing description of the present invention has been presented by way of illustration and example only and in certain preferred embodiments. Accordingly, the present invention has many modifications, without departing from its essence,
It will be apparent to those skilled in the art that variations can be made. For example, the drive voltage waveform is a sine waveform, but may be a rectangular waveform. The scope of the present invention defined by the description in the claims section is intended to cover alterations and modifications within the scope.

[0030]

As described above, according to the present invention, two opposing heating elements constituting a bridge are disposed so as to face a non-uniform magnetic field, and the other two opposing heating elements are arranged in a magnetic field. And the bridge is supplied with an AC voltage from an AC power supply, so that it is possible to realize a high-accuracy magnetic oximeter with few components without being affected by posture and temperature drift.

Further, the two opposite heating elements constituting the entire bridge are arranged in a region where the intensity of the magnetic field changes (non-uniform magnetic field).
And the other two heating elements are arranged in the vicinity of the two heating elements, so that the output of the bridge becomes larger than that of the embodiment shown in FIG. / N can be improved.

If two of the components constituting the bridge are inexpensive carbon film resistors, the overall cost can be reduced.

[0033]

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an example of an embodiment of a magnetic oximeter of the present invention.

FIG. 2 is a diagram showing output waveforms 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 configuration diagram showing an example of an embodiment according to claim 2 of the present invention.

FIG. 6 is a configuration diagram showing an example of an embodiment according to claim 4 of the present invention.

FIG. 7 is an explanatory diagram of a measurement principle of the present invention.

FIG. 8 is an explanatory diagram of the measurement principle of the present invention.

FIG. 9 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

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kentaro Ma 2-9-32 Nakamachi, Musashino-shi, Tokyo F-term in Yokogawa Electric Corporation (reference) 2G053 AA05 AB06 AB17 BB11 BB16 CA13 CA18 CA19 CB05

Claims (4)

[Claims] 1. A magnetic field generating means for generating a magnetic field from magnetic poles disposed opposite to each other, an all-bridge formed by four equivalent heating elements which generate heat when energized and have a variable resistance value, and an AC power supply. The two opposing heating elements forming the entire bridge are arranged to face a region (non-uniform magnetic field) where the intensity of the magnetic field changes, and the other two opposing heating elements are not affected by the magnetic field. A magnetic oximeter, wherein the oximeter is disposed at a position and an AC voltage is applied from the AC power source to all the bridges. 2. A magnetic field generating means for generating a magnetic field from magnetic poles disposed opposite to each other, an all-bridge formed by four equivalent heating elements which generate heat when energized and whose resistance value changes, and an AC power supply. The two opposing heating elements forming the entire bridge are arranged to face a region where the magnetic field intensity changes (non-uniform magnetic field), and the other two opposing heating elements are located near the two heating elements. Wherein an AC voltage is applied to the bridges from the AC power supply. 3. The magnetic oximeter according to claim 1, wherein the heating element is made of tungsten (W), silicon, a silicon compound, or platinum (Pt). 4. A magnetic field generating means for generating a magnetic field from magnetic poles disposed opposite to each other, two equal heating elements which generate heat when energized and whose resistance value changes, and two resistors having the same resistance value. A half-bridge and an AC power supply, wherein the half-bridge is connected such that a heating element and a resistor are adjacent to each other, and arranges one of two opposing heating elements in a region where the intensity of the magnetic field changes. A magnetic oximeter characterized in that the other heating element is arranged at a position where the influence of the magnetic field does not affect, and an AC voltage is applied from the AC power supply to the opposite connection point.