JP3243596B2 - Oxygen analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an oxygen analyzer for measuring the concentration of oxygen in a gas to be measured.

[0002]

2. Description of the Related Art As a technique for analyzing oxygen, there is a technique using magnetism. The paramagnetism of oxygen is 1851 according to Faraday.
A magnetic wind oximeter is one of the analyzers that was discovered in 2000, and uses the paramagnetism of oxygen. FIG. 3 is a configuration diagram showing a schematic configuration of the magnetic wind oximeter. In the figure, 31 is a sample introduction part, 32 is a sample discharge part, 33 is a cell in which a reference side filament 34 is arranged, 35 is a cell in which a measurement side filament 36 is arranged, and 37 is a cell 35
It is a magnet arranged on the side. The reference side filament 34 and the measurement side filament 36 form a part of the arm of the Hoiston bridge.

In the above configuration, when oxygen is not contained in the sample gas introduced from the sample introduction section 31 and exiting from the sample discharge section 32, the sample gas is supplied to the cells 33 and 35.
Both diffuse equally and the bridge by the reference filament 34 and the measurement filament 36 balances. Here, if oxygen exists in the sample gas, the oxygen is
It is attracted to the magnetic field by 7 and is sucked into the cell 35. However, when this oxygen is heated by the measurement side filament 36 and the temperature rises, the magnetic susceptibility decreases and is replaced by the low-temperature oxygen in the flowing sample gas. The convection caused by the above, that is, the magnetic wind lowers the temperature of the measurement side filament 36, and the bridge becomes unbalanced. By detecting this, oxygen can be analyzed.

[0004]

Conventionally, the above-mentioned configuration has the following problems.
First, in the above-described conventional oximeter, if the cell in which the measurement-side filament is arranged is filled with oxygen, it is not possible to measure a further concentration. Secondly, the conventional oxygen meter has a problem in that it requires a reference gas for calibration to flow through the flow path of the sample gas for calibration, which is troublesome.

The present invention has been made to solve the above problems, and has as its object to enable measurement of a higher oxygen concentration and to further simplify calibration.

[0006]

An oxygen analyzer according to the present invention comprises: a cell disposed in a flow path through which a gas to be measured flows;
A purge gas introduction unit for introducing a purge gas made of a gas having a different thermal conductivity from oxygen to the cell, a valve installed in the purge gas introduction unit to control the introduction of the purge gas, a discharge unit for discharging gas in the cell, and a cell. It is provided with a gas exchange membrane through which a partition gas passes through the flow path, a thermal conductivity detecting means disposed in the cell, and a magnet for generating a magnetic field from the rear of the thermal conductivity detecting means toward the gas exchange membrane. I made it.
For this reason, when the gas to be measured is introduced into the cell, the oxygen therein is attracted to the magnet and reaches the thermal conductivity detecting means faster than the others.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing a configuration of an oxygen analyzer according to an embodiment of the present invention, wherein 1 is a flow path through which a process gas to be measured passes, and 2 is a TCD sensor 3.
A cell 4 in which (thermal conductivity detecting means) is disposed is a gas exchange membrane disposed above the cell 2 and separating the flow path 1 and the cell 2 from each other.
Is a purge gas introduction unit for introducing a purge gas into the cell 2,
6 is a discharge unit for discharging gas in the cell 2, 7 is a valve attached to the purge gas introduction unit 5, and 8 is a TC in the cell 2.
It is a permanent magnet that applies a magnetic field toward the gas exchange membrane 4 in the area where the D sensor 3 is arranged. Helium gas or nitrogen gas having a different thermal conductivity from the oxygen gas to be measured may be used as the purge gas. As the gas exchange membrane 4, a membrane made of a sintered metal or a fluororesin may be used.

FIG. 1 (b) shows a constant temperature difference drive T
FIG. 2 is a configuration diagram showing a configuration of a CD sensor 3, wherein a reference numeral 11 denotes a resistance temperature detector (TCD) arranged in a supply passage of a gas to be measured;
R1, R2, R3, R _R2 are resistors, 13 is a comparator,
The resistance bulb 11 and the resistance R _R2 in the area indicated by the dotted line constitute a measurement section that directly or indirectly touches the gas to be measured. A Wheatstone bridge is formed by the TCD 11 and the resistors R1, R2, and R3, and a circuit including the bridge and the comparator 13 controls the current so that the temperature of the TCD 11 is always constant. The resistance R _R2 is a resistance for temperature measurement. By setting the resistances R1, R2, and R3 to predetermined values, the heat generation temperature T _Rh of the TCD 11 is obtained.
And the temperature difference from the ambient temperature T _RR2 becomes a constant value,
The current i flowing to the TCD 11 is controlled.

Hereinafter, measurement of the thermal conductivity will be described first. When the gas to be measured is supplied to the TCD sensor 3 shown in FIG. 1, heat proportional to the thermal conductivity of the gas is taken from the TCD 11 in the TCD sensor 3. As a result, the heat generation temperature T _{Rh of the} TCD 11 that is to be kept at a constant temperature changes, and the resistance value Rh changes. At this time, the resistance R1
The voltage generated at the connection point between TCD11 and TCD11 is applied to the inverting input of comparator 13 as output voltage V. On the other hand, the resistance R
2 (and R _R2 ) and the voltage at the connection point of the resistor R 3 are applied to the non-inverting input of the comparator 13. And TCD1
1 is detected as a change ΔV in the output voltage V.

The comparator 13 controls the current i flowing to the TCD 11 on the basis of the detected change ΔV of the output voltage V to make the resistance Rh of the TCD 11 constant (Rh = (R1 × R
2) Keep at / R3). As a result, the output voltage V changes, and the heat generation temperature _{Rh of the} TCD 11 is kept constant. TCD
The fact that the exothermic temperature T _Rh of No. 11 is kept constant can also be seen from the following equation (1). That is, the TCD 11 is a resistor made of a thin film such as platinum, and its resistance value Rh is expressed by the equation (1). When the resistance value Rh of the TCD 11 is controlled to be constant, the heat generation temperature T _Rh is also kept constant. .

Rh = Rh ₂₀ {1 + α ₂₀ · (T _Rh− 20) + β ₂₀ · (T _Rh− 20) ² } (1) In the formula (1), Rh ₂₀ is TC at 20 ° C.
The resistance value (Ω) of D11 and α ₂₀ are TCD1 at 20 ° C.
1 of the primary resistance-temperature coefficient, TCD 1 in beta ₂₀ is 20 ° C.
1 is the secondary resistance temperature coefficient.

Here, the amount of heat Q _T transmitted from the TCD 11 to the surroundings is expressed by the following equation (2). In equation (2), Q _G is the amount of heat transmitted to the gas to be measured by heat conduction,
Q _S diaphragm to build a TCD11 (silicon)
And amount of heat transferred to the silicon base through the resistor pattern, Q _C is the amount of heat transferred by convection (forced convection and natural convection), Q _R is the amount of heat transferred by radiation. Q _T = Q _G + Q _S + Q _C + Q _R (2)

The heat quantity Q _T in the equation (2) is further expressed as the following equation (3). In this equation, T _RR2 is the temperature of the atmosphere (° C.), λm is the thermal conductivity of the gas to be measured (w / km), G is the device constant (m),
λ _si is the thermal conductivity of the diaphragm and the resistor pattern (w
/ K · m), G _S is a device constant in the diaphragm and resistor pattern (m). _{Q T = (T Rh -T RR2} ) · λm · G + (T Rh -T RR2) · λ si · G S + Q C + Q R ··· (3)

[0014] In this equation (3), G and G _S is not changed by the gas composition, Q _C, Q _R is sufficiently small value compared to the Q _G, Q _S (or constant value), lambda _si also It is considered constant. If T _Rh and T _RR2 are controlled to be substantially constant, the above equation (3) can be expressed by the following equation (4), where A and B are intrinsic device constants (shape factors including the operating state). On the other hand, it can also be expressed by the following equation (5). Q _T = A · λm + B (4) Q _T = i ² · Rh = V ² / Rh (5)

Then, Q _T = A · λm + B = V ² / Rh
Therefore, the thermal conductivity λm of the gas to be measured is given by the following (6)
It is represented by the formula. λm = (V ² / Rh-B) / A (6)

Here, the unique device constants A and B are divided.
For example, by substituting the output voltage V into the above equation (6),
The thermal conductivity λm of the gas to be measured can be obtained. Ma
In this circuit, as described above,
Resistance R_R2R1 × (R_R2+ R2) = R3 × Rh (7) R3 × Rh−R1 × R_R2= R1 × R2 (8), and R1 × R2 is constant. R_R2Changes,
R3 × Rh-R1 × R_R2 = R1 × R2
Then, the current i flowing to the TCD 11 is controlled, and the value of Rh is
Change. Therefore, the ambient temperature T_RR2Changes so much
If not, use this circuit to set up a thermostat
Even if it is not, the thermal conductivity of the gas in the atmosphere is relatively accurately λm
Is possible.

In the above-described configuration, the valve 7 is intermittently opened and closed, and the introduction and stop of the purge gas into the cell 2 are repeated, whereby the oxygen concentration in the process gas flowing in the flow path 1 can be measured. . That is, when the introduction of the purge gas into the cell 2 is stopped by closing the valve 7, the process gas diffuses into the cell 2 via the gas exchange membrane 4. Then, in this process gas, particularly, oxygen is selectively attracted to the permanent magnet 8 and comes to the vicinity of the TCD sensor 3. On the other hand, if oxygen does not exist in the process gas, the process gas diffuses and comes to the vicinity of the TCD sensor 3 without being attracted by the magnetic force.

Therefore, as shown in FIG. 2, the change in the output (thermal conductivity) of the TCD sensor 3 after the introduction of the purge gas is stopped is different between the above two cases, and the case where oxygen is present. Changes faster. In FIG. 2, 2
1 is an output waveform of the TCD sensor 3 (FIG. 1) when oxygen is not present in the process gas, and 22 is an output waveform of the TCD sensor 3 when oxygen is present in the process gas.
At the time of measurement, the introduction of the purge gas into the cell 2 is stopped at t0, and the introduction of the purge gas into the cell 2 is restarted at t2. At this time, the output waveform of the TCD sensor 3 from t0 to t
It is determined whether or not this detection result indicates that oxygen is present, based on the rising gradient between the two.

As described above, if oxygen is present in the process gas, the oxygen is attracted to the permanent magnet 8 and is detected by the TCD sensor 3 faster than other process gas components approaching by diffusion. become. Therefore,
When oxygen does not exist, for example, as shown in the output waveform 21 of FIG. 2, the rise of the sensor output is slow. On the other hand, when oxygen is present, the rise of the sensor output is fast as shown in the output waveform 22 of FIG. 2, for example. Therefore, for example, when the sensor output at time t1 is equal to or more than a predetermined value, it may be determined that oxygen has been detected.

For example, in FIG. 2, the sensor output v1 at time t1 is equal to or greater than a predetermined value, so that it is determined that oxygen is present at this time, and the sensor output v2 at time t1 is equal to or less than the predetermined value. Judge that there is no oxygen.
Then, in the output waveform 22 when it is determined that there is oxygen, the oxygen concentration at that time is obtained from the value of the sensor output v3 at the time t2. When purging,
The purge gas flows back through the gas exchange membrane 4, and dust on the surface of the gas exchange membrane 4 in the flow path 1 can be removed. In the measurement, the purge gas is intermittently introduced into the cell, and during this purge, a state is created in which there is no oxygen in the cell. That is, zero calibration is performed sequentially.

[0021]

As described above, according to the present invention, a cell disposed in a flow path through which a gas to be measured flows, and a purge gas introduction unit for introducing a purge gas comprising a gas having a different thermal conductivity from oxygen into the cell. A valve installed in the purge gas introduction unit to control the introduction of the purge gas, a discharge unit that discharges gas in the cell, a gas exchange membrane that separates the cell from the flow path, and a gas exchange membrane that passes through the cell, and are disposed in the cell. And a magnet for generating a magnetic field from the rear of the thermal conductivity detecting means toward the gas exchange membrane. Therefore, in the present invention, when the introduction of the purge gas into the cell is stopped, the gas to be measured diffuses into the cell through the gas exchange membrane, and the oxygen in the gas is attracted to the magnet and heat conduction is performed faster than the others. It reaches the rate detecting means. As a result, according to the present invention, a higher oxygen concentration can be measured by intermittently turning on and off the introduction of the purge gas into the cell, and
There is an effect that calibration in concentration measurement can be further simplified.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of an oxygen analyzer according to an embodiment of the present invention.

FIG. 2 is a waveform chart showing a change in the output of the TCD sensor 3.

FIG. 3 is a configuration diagram showing a schematic configuration of a conventional magnetic wind-type oximeter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Flow path, 2 ... Cell, 3 ... TCD sensor (thermal conductivity detection means), 4 ... Gas exchange membrane, 5 ... Purge gas introduction part, 6 ...
Discharge unit, 7: valve, 8: permanent magnet.

Claims (1)

(57) [Claims] 1. A cell disposed in a flow path through which a gas to be measured flows, a purge gas introduction unit for introducing a purge gas made of a gas having a different thermal conductivity from oxygen to the cell, and a purge gas introduction unit installed in the purge gas introduction unit. A valve for controlling the introduction of the purge gas, a discharge unit for discharging gas in the cell, a gas exchange membrane that partitions the cell and the inside of the flow path, and a gas that passes therethrough, and heat disposed in the cell. An oxygen analyzer comprising: a conductivity detector; and a magnet that generates a magnetic field from the rear of the thermal conductivity detector toward the gas exchange membrane.