JPS60207053A - Magnetic wind type oxygen meter - Google Patents

Abstract

PURPOSE:To remove the interference of carbon dioxide, by amplifying the change in the resistance of the detection elements provided to a measuring chamber and a comparison chamber by two independent amplifiers and adjusting the output voltages thereof so as to bring the same to the same value when reference gas is flowed in. CONSTITUTION:The changes in the resistance values of detection elements 4a, 4b are respectively independently detected in such a state that only nitrogen gas is flowed into a measuring chamber 1 to which a magnetic field is applied and a comparison chamber 2 to which no magnetic field is applied and variable resistors 12, 11 of the bridge circuit including the detection elements are adjusted so as to bring input voltage of amplifiers 16, 17 to zero. Next, a predetermined amount of a gaseous mixture of nitrogen gas and carbon dioxide is flowed into the measuring chamber 1 and the comparison chamber 2 and variable resistors 18, 19 provided to the amplifiers 16, 17 are adjusted so as to bring the output voltage of the amplifiers to the same value. By this method, the interference of carbon dioxide is removed. These voltages having the same value are inputted to a voltage comparison circuit 20. By this constitution, it is unnecessary to provide a mechanical correction mechanism to the comparison chamber and manufacturing becomes easy.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a magnetic wind hole oxygen meter, and further relates to an improvement in a correction mechanism for carbon dioxide interference.

(b) Conventional Example A conventional magnetic wind hole oxygen meter is designed to consist of a measurement chamber and a comparison chamber that have the same structure, and measures oxygen concentration by applying a magnetic field to the measurement chamber. That is, if oxygen is present in the measurement gas, it will be attracted to the center where the magnetic field is strongest. Oxygen that reaches the center is heated by a detection element made of a hot wire, reduces its magnetic susceptibility, weakens the attraction force, and is then pushed away by the sucked oxygen. A continuous flow of gas (magnetic wind) is thus created, the strength of which is proportional to the oxygen concentration in the gas. In addition, natural convection occurs, but due to the dung being cooled by the magnetic wind, the change in resistance of the sensing element in the measurement chamber to which a magnetic field is applied is greater than that of the sensing element in the comparison chamber to which no magnetic field is applied.

This difference is detected by a bridge circuit and the oxygen concentration is measured.

As mentioned above, although the measurement chamber and the comparison chamber have the same design, there are subtle structural differences, and their capacities often differ slightly. Carbon dioxide gas has a very high thermal conductivity, so if the amount of gas contained in the measurement chamber and the comparison chamber is different, and there is a corresponding difference in the amount of carbon dioxide gas, the temperature of the detection element in both chambers will change. The difference in change will be affected by the difference in the amount of carbon dioxide gas, making it impossible to measure the oxygen concentration accurately.

The above phenomenon is known as carbon dioxide interference, and in order to correct this, conventionally the volume in the comparison chamber was changed by a mechanical mechanism to make it equal to the volume in the measurement chamber. However, this mechanical correction mechanism has a complicated structure, which increases manufacturing costs, and moving the correction mechanism changes the structure of the comparison chamber, which causes disturbance to the internal detection element, making it difficult to maintain a stable state. It takes 4 to 5 minutes to reach this point, which has the disadvantage that it takes a long time for correction.

(c) Purpose This invention was made in view of the above circumstances, and provides a magnetic wind type oximeter having a simple configuration and a correction mechanism for carbon dioxide interference that does not require a long correction time.

B) Structure And in this invention, a correction circuit for carbon dioxide interference is connected to a bridge circuit with the detection elements in both chambers on one side. A comparison chamber having substantially the same structure as the measurement chamber without the addition of a bridge circuit,
In a magnetic wind oxygen meter consisting of a power source for the bridge circuit and an indicator connected to the bridge circuit to indicate the oxygen concentration, 11 voltages are output from the bridge circuit corresponding to each detection element to the bridge circuit. and two independent amplifier circuits with variable amplification and
A magnetic wind system characterized in that a correction circuit for carbon dioxide interference is connected to a voltage comparison circuit that generates a signal indicating 0 when the output pressures of the independent amplifier circuits are compared and they match. It is an oxygen meter.

(e) Examples Examples of the present invention will be described below in detail with reference to the drawings, but the invention is not limited to the following examples. First, the structure of a magnetic wind type oxygen meter will be explained with reference to FIG. explain.

It consists of a measurement chamber il+ and a comparison chamber +2 which have approximately the same structure, and an external permanent magnet +31. A magnetic field is applied to the comparison chamber +31, and no magnetic field is applied to the comparison chamber +21.

In the center of the compartment fil, +21 is a roughly ring-shaped oxygen concentration detection element (4a) + (4b) made of a noble metal wire such as platinum.
) are installed respectively, and in the measurement chamber 11+, the center position is the part where the magnetic field is strongest. fl+l is the measuring gas conduit, (6) is the respective chamber fl+, (21
This is the measurement gas introduction hole.

The basic measurement operation of oxygen concentration in the above structure will be briefly explained.

Each of the detection elements (4a) and (4b) constitutes one side of the bridge circuit shown in FIG. 2, and a DC stabilized power supply is connected to the bridge circuit.

Heat (4b) to 300-400°C. Art studio fi+
.

(In 21 yen, the introduced measurement gas is detected by the detection element (4a)
.

(4b) generates thermal convection, and in the measurement chamber (1), the rv&element in the measurement gas is influenced by the magnetic field, which is called magnetic wind as shown in the conventional example section. Gas flow occurs along with thermal convection. The magnetic wind cools the detection element (4a) in the measurement chamber fl+ more than the detection element (4b), and as a result, the resistance value of the detection element (4a) changes by 1, which causes the constructed bridge circuit to become unbalanced and lower the oxygen concentration. A voltage corresponding to the voltage is generated.

Next, with reference to FIG. 2, a carbon dioxide interference correction circuit, which is a characteristic configuration of the present invention, provided in the magnetic wind type oxygen meter having the above configuration will be explained, including a bridge circuit.

Detection elements (4a) and (4b) are resistors (7) 1 (8
L (9+, tlol constitute a bridge circuit, and the resistors (91, (Io) are each connected to a variable resistor toL'
H are connected in parallel, and a DC stabilized power supply (+3) is further connected. From each output end (14) and output end (16) of this bridge circuit to each detection element (4)
The voltage corresponding to a) and (4b) is output.

This output voltage is input to the carbon dioxide interference correction circuit (2 匈).

Each amplifier (161, 07) connected to each output terminal (14>105) of the bridge circuit has a variable resistor θ8L (19+
Equipped with

Amplifier θ61. The output of (17) is connected to the next stage voltage comparison circuit (20), and the voltage comparison circuit (20) is connected to an indicator (21) that indicates the oxygen concentration.

Next, the correction operation of this embodiment will be explained.

First, a measurement gas consisting only of nitrogen gas is introduced into the measurement chamber +11 and the comparison chamber (2+), and the input signal voltage (eA) of the amplifier (I
Vi rub. Next, the input signal voltage (Qe
) is rubbed by OmVi by varying the variable resistor (11).

After completing the above adjustments, move the measurement room (lj) and comparison room (2)
A measurement gas, which is a mixture of about 80% nitrogen gas and about 20% carbon dioxide gas, is introduced into the sample. At this time, a voltage corresponding to the thermal conductivity of carbon dioxide gas is generated in each of the input signal voltages (C?A) and (IQ9). (jA=Qt
There is no problem if it becomes a, but measurement room i11 and comparison room (2)
9A>eg or eA< due to subtle structural differences between
The relationship becomes Q[11. The difference between eA and e8 is that the variable resistor (+
8), +19), the amplifier (16
The output voltages of 11 (17+) are made to have the same value. This same value voltage is applied to the next stage voltage comparison circuit (20
), since the two input voltages match, the oxygen concentration indicator (21) connected to the 1E pressure comparator circuit (20) indicates 0%.

In this example, a single differential amplifier circuit with a voltage comparator circuit is illustrated, but it can also be configured with a digital voltage comparator circuit including an AD conversion circuit, and in this way, a correction circuit that can obtain the same or better accuracy can be constructed. can get. - The main bridge circuit may also be composed of two independent bridge circuits, each with g detection elements as elements on one side.

The correction circuit in Embodiment Z described above is just one example, and the amplifier temperature correction circuit, offset 5B1 circuit, etc. may be added as appropriate to obtain the required performance.

(f) Effects According to this invention, the configuration is simple and the correction tone is correct! A magnetic wind type oxygen meter can be obtained which requires less time for 'A' and has excellent viscosity.

In particular, since it is not necessary to provide the 4-geometric correction mh= in the comparison chamber, the measurement chamber and the comparison chamber can have the same structure, resulting in easy manufacturing and low cost.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of an embodiment of a magnetic wind type oxygen meter used in this invention, and FIG. 2 is a circuit diagram of an embodiment of a correction circuit used in this invention. (1) Measurement room, (21... comparison room, (4a), (
4b)...Detector, 0■-DC stabilized power supply, (lfl
l+ (17)・Amplification circuit, (/:0)・Voltage comparison circuit, Indicator, (Figure...Correction circuit for carbon dioxide interference. 1. Agent: Patent attorney Shintabe Nogawa jv pa

Claims (1)

[Claims] 1. A measurement chamber to which a magnetic field is applied, a comparison chamber to which no magnetic field is applied and which has substantially the same structure as the measurement chamber, and a detection element installed in each chamber to detect the oxygen concentration in the gas; In a magnetic wind hole oxygen meter comprising a bridge circuit with each detection element as an element on one side, a power supply for the bridge circuit, and an indicator connected to the bridge circuit to indicate oxygen 0 degrees, the bridge circuit has: Two independent amplifier circuits each receive the voltage output from the bridge circuit corresponding to each detection element and the amplification degree is variable, and the output voltages of these two independent amplifier circuits are compared and matched. 1. A magnetic wind hole oxygen meter, characterized in that a correction circuit for carbon dioxide interference is connected thereto, and a voltage comparison circuit that generates a signal indicating O when the oxygen is detected.