JPH0414304B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention uses a solid electrolyte element to measure the oxygen concentration in a measurement gas containing water vapor and the oxygen concentration in a comparison gas obtained by removing water vapor from the measurement gas. By obtaining a signal according to the ratio of Concerning configuration.

[Prior art and its problems]

BACKGROUND ART A moisture measuring device for measuring water vapor, ie, water concentration, in a measurement gas containing water vapor and oxygen using a solid electrolyte oxygen concentration detector is known, and the measurement principle of this measuring device is as follows.

That is, let the volume of the measurement gas be V, the volumes of water vapor, oxygen, and other gases in this volume V be V _w , V _p and V _a , and the concentrations of water vapor and oxygen in the measurement gas be A, respectively. _w and
When A _p is set, equations (1) and (2) are obtained.

V = V _w + V _p + V _a ...(1) A _w = V _w /V, A _p = V _p /V ... (2) Next, when dry gas is obtained by removing water vapor from the measurement gas, this The concentration A _pr of oxygen in the gas is expressed by equation (3).

A _pr = V _p / (V _p + V _a ) ... (3) Therefore, the measurement gas containing water vapor and the dry gas obtained by removing water vapor from this measurement gas are respectively connected to the measurement electrode part of the solid electrolyte oxygen concentration detector. When it is guided to the reference electrode section, an electromotive force E shown in equation (4) is generated between the two electrodes of the detector, and equation (4) can be calculated using equations (1) to (3).
It can be rewritten as equation (5). Here, K is a proportionality constant.

E=K・_lo (A _pr /A _p ) ……(4) E=−K・_lo (1−A _w ) ……(5) Therefore, by measuring the electromotive force E, the concentration A _w
A moisture measuring device using a solid electrolyte oxygen concentration detector measures the water vapor concentration A _w in this way, and as long as the moisture measurement is performed in the manner described above, this measurement result will indicate the oxygen concentration.
It is clear from equation (5) that it is not affected by A _p .

However, as is clear from the above, the oxygen concentration A _pr used in this measuring device must be that of the dry gas obtained by dehumidifying the measurement gas exhibiting the oxygen concentration A _p ; When the concentration A _p fluctuates within a short time and dry gas with an oxygen concentration A _pr1 is introduced into the reference electrode section of the concentration detector, the dry gas with an oxygen concentration A _pr1 is introduced into the measurement electrode section of the concentration detector. If a measurement gas having an oxygen concentration A _p2 different from the oxygen concentration A _p1 of the original measurement gas from which the gas was generated is introduced, an error will occur in this measuring device.

For this reason, the following measurement methods have been proposed in the past. In other words, in this measurement method, two oxygen concentration detectors are used; one oxygen concentration detector is supplied with a measurement gas containing moisture, and the other oxygen concentration detector is supplied with a gas from which moisture has been removed. If there is a difference in the speed of each gas reaching each of these two oxygen concentration detectors, the detection signal of the oxygen concentration detector of the faster gas is delayed through a delay circuit, and the Synchronize the detection signals of the oxygen concentration detectors. With this kind of synchronous calculation processing,
Accurate water concentration signals that are not affected by changes in oxygen concentration can be obtained. However, it requires two oxygen concentration detectors and one signal delay circuit, making the device complex and expensive.

Other measurement methods have also been proposed as follows. It has one solid electrolyte type oxygen concentration detector, a gas sampling pipe having a gas sampling port into which a measurement gas is introduced at its extended tip, and a gas inlet provided close to the gas sampling port. a dehumidifier that introduces and dehumidifies the measurement gas through a gas inlet; a gas extraction port that opens on the oxygen concentration detector side of the gas sampling pipe; and a measurement gas containing moisture that reaches the oxygen concentration detector. By providing a time lag adjustment means for adjusting the time lag of the gas from which moisture has been removed, two conventional oxygen concentration detectors can be reduced to one, and the measurement electrode and reference electrode of the solid electrolyte oxygen concentration detector can be combined into one. It is possible to match temporal fluctuations in the oxygen concentration in the gas that reaches .

However, since these methods all compare moisture-containing oxygen and dry oxygen at the same oxygen concentration, the dry oxygen reaching the reference electrode is delayed by the time required for dehumidification, and this dehumidification time If fluctuations in oxygen concentration occur during the test, it is meaningless to compare moist oxygen and dry oxygen, and there is a problem that moisture measurement becomes impossible, and the time delay of dry oxygen reaching the reference electrode is Since this is unavoidable, it is necessary to shorten this time delay as much as possible in a moisture measuring device using a solid electrolyte type oxygen concentration detector.

[Purpose of the invention]

The present invention solves the above-mentioned conventional problems in moisture measuring devices using solid electrolyte oxygen concentration detectors, and even if the oxygen concentration in the measurement gas fluctuates within a short period of time, measurement errors due to these fluctuations occur. It is an object of the present invention to provide a moisture measuring device in which almost no occurrence of moisture occurs.

[Key points of the invention]

In order to achieve the above-mentioned object, the present invention provides a moisture measuring device including a gas reservoir chamber provided with a pore into which a measuring gas containing water vapor and oxygen flows, and a measuring electrode and a comparison electrode on each of both surfaces. a solid electrolyte type oxygen concentration detector having a solid electrolyte element arranged in the gas reservoir so that the measurement gas introduced into the gas reservoir comes into contact with the measurement electrode; and a comparison gas supply mechanism that sucks in the measurement gas, dehumidifies it with a dehumidifier, dries it, and supplies it to the comparison electrode section of the solid electrolyte oxygen concentration detector,
Furthermore, the dehumidification device is composed of first and second semipermeable membrane vapor phase dehumidifiers and a pump, and the pump supplies the source gas to the second semipermeable membrane vapor phase dehumidifier to extract the source gas from the source gas. A dehumidified purge gas is obtained, and the measurement gas is made to flow through the first semipermeable membrane vapor phase dehumidifier, and the purge gas is supplied to dry the measurement gas, and the water vapor in the measurement gas is detected by the oxygen concentration detector. The device is designed to measure the concentration, that is, moisture, and by configuring the moisture measuring device in this way, short-term fluctuations in the oxygen concentration in the measurement gas can be detected within the gas reservoir. The measurement gas is averaged by the tank action of the chamber, and the volume of the measurement gas flow path in the comparison gas supply mechanism including the first semipermeable membrane gas phase dehumidifier is reduced, so that the measurement gas is supplied to the measurement electrode of the oxygen concentration detector. The time lag between the time of contact and the time when this measurement gas is dried by the reference gas supply mechanism and contacts the reference electrode of the detector is shortened, so that the moisture measurement based on the time lag is This is to reduce the error.

[Embodiments of the invention]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of an embodiment of the moisture measuring device according to the present invention, and FIG. 2 is a diagram explaining the principle of FIG. 1. In both figures, 1 is a measurement gas containing oxygen and water vapor present in a space surrounded by a furnace wall 2, and 3 is a flange 3b fixed to one end of a cylindrical skirt 3a with internal threads. This support member 3 is fixed to a disc-shaped main body mounting base 4 by a flange 3b, and one end of the skirt 3a is closed with a cover 7 having at least one pore 6 formed therethrough. The other end of the cylindrical body 5 is screwed. Reference numeral 8 denotes a gas reservoir chamber surrounded by the main body mount 4, the cylinder 5, and the cover 7. The gas reservoir chamber 8 is placed in the atmosphere of the measurement gas 1 by attaching the main body mount 4 to the furnace wall 2. A porous filter 9 is placed at the tip of this gas reservoir chamber 8 so as to cover the cover 7.
is provided. Reference numeral 10 denotes a bottomed cylindrical solid electrolyte element, for example a zirconia element, which has a measuring electrode 11 and a comparison electrode 12 on the outer and inner surfaces of the bottom, respectively. 13 is the electrode 1.
1 and 12 and a zirconia element 10. The solid electrolyte oxygen concentration detector 13 is constructed by fixing a solid electrolyte element, which has a measuring electrode and a comparison electrode on the front and back surfaces of a flat solid electrolyte pellet, in a ceramic support, for example, in a cylinder. Even if the electrolyte element and the support are formed into a bag shape with a reference electrode on the inner surface, and the opening of this bag shape projects from the main body mounting base 4 to the outside of the gas reservoir chamber 8. good.

Reference numeral 14 denotes a gas sampling pipe which is installed through the main body mounting base 4 so that one end 14a is disposed within the gas reservoir chamber 8 and the other end protrudes outside the gas reservoir chamber 8, and 15 is a gas sampling pipe whose one end is disposed in the vicinity of the reference electrode 12. A gas injection tube 16 is inserted through a lid 10a provided at the end opposite to the zirconia element 10 and the bottom so as to face the electrode 12, and its suction port 16a is connected to a conduit 18 for gas collection. A first pump 17 is connected to the end of the pipe 14 that protrudes outside the gas reservoir chamber 8;
The first semipermeable membrane vapor phase dehumidifier is connected to the discharge port 16b of the dehumidifier 17, and has a double pipe structure with an inner pipe and an outer pipe into which the inner pipe is loosely inserted. The other end 17b of the pipe is connected to the gas injection pipe 15 by a conduit 20.
The end of the zirconia element 10 is connected to the outside of the zirconia element 10 . 21 is a conduit whose one end is open to the atmosphere and the other end is connected to the suction port 22a of the second pump 22; and 23, one end 23a of the semipermeable membrane inner tube is connected to the discharge port of the second pump 22 through a conduit 24. 22b, the second semipermeable membrane vapor phase dehumidifier is formed into a double pipe structure with an inner pipe and an outer pipe into which the inner pipe is loosely inserted, and the other end of the inner pipe of the dehumidifier 23 is 23b is connected to the purge gas inlet 17c provided in the outer tube of the first semipermeable membrane vapor phase dehumidifier 17 by a conduit 26 via a needle valve 25, and is connected to a conduit 28 via a needle valve 27. is connected to the purge gas inlet 23c provided in the outer pipe of the dehumidifier 23 itself,
Each purge gas outlet 17d and 23d of the first and second semipermeable membrane gas phase dehumidifiers 17, 23 are both open to the atmosphere. 29 is a frame fixed to the main body mounting base 4, 30 is a cover of the frame 29, 31 is a terminal block of the oxygen concentration detector 13, and the first dehumidifier 17
is fixed to the end of the oxygen concentration detector 13 within the frame 29, and the second dehumidifier 23, first and second pumps 16, 22, and terminal block 31 are all fixed within the frame 29.
is attached to. 32 is a moisture measuring device consisting of the above-mentioned members except for the furnace wall 2.

Since this moisture measuring device 32 is configured as described above, when the second pump 22 is operated, air is sucked into this pump 22 through the conduit 21, and pressure is applied by this pump to the second pump 22. Air is sent into the inner pipe of the dehumidifier 23 by the conduit 24, and the air that has flowed through the inner pipe and flows out from the end 23b is in the space between the inner pipe and the outer pipe of the second dehumidifier 23. A part of the air sequentially flows through the needle valve 27 and the purge gas inlet 23c, and the rest of the air that flows out from the end 23b passes through the needle valve 25 and the purge gas inlet 17c in order, and then flows into the first dehumidifier 1.
The air that flows into the space between the inner pipe and the outer pipe in the first and second dehumidifiers 17 and 23 also flows into the space between the inner pipe and the outer pipe in the purge gas flow. It flows out into the atmosphere from outlets 17d and 23d. That is, in this case, in the second dehumidifier 23, the pressure inside the inner tube becomes higher than the pressure outside the inner tube, so water vapor in the air inside the inner tube passes through the semipermeable membrane inner tube and moves to the outside of the inner tube. As a result, the air guided to the purge gas inlet 17c of the first dehumidifier 17 via the needle valve 25 becomes dehumidified dry gas.

Therefore, in this moisture measuring device 32, when the first pump 16 is operated while the second pump 22 is operated, the measurement gas 1 is removed by the filter 9 and then passes through the pores 6 into the gas reservoir chamber 8. At the same time, a part of the measurement gas is collected from one end 14a of the gas sampling pipe 14, passes through a conduit 18, a pump 16, and a conduit 19 in order and is sent to a first dehumidifier 17. The first
In the dehumidifier 17, as described above, the dry air obtained by the second dehumidifier 22 is transferred to the purge gas inlet 17.
Since the sample gas is introduced from the conduit 19 into the inner tube of the first dehumidifier 17, the water vapor in the sample gas passes through the semi-permeable membrane inner tube and moves into the dry air. As a result, the measurement gas is dehumidified and dried by the first dehumidifier 17, and the measurement gas is brought into contact with the reference electrode 12 through the conduit 20 and the gas injection tube 15 in sequence, and then the measurement gas is is discharged to the atmosphere through a through hole 10b provided in the lid 10a and a conduit (not shown) in sequence. In other words, in this case, the measuring gas containing water vapor comes into contact with the measuring electrode 11, and the dehumidified measuring gas comes into contact with the reference electrode 12, so that an electromotive force appears between the two electrodes depending on the water vapor concentration in the measuring gas. . In the above-described embodiment, air is sucked as a source gas from the conduit 21 by the second pump 22, and this air is dehumidified by the second semipermeable membrane vapor phase dehumidifier 23 and used as a purge gas to be used as a purge gas in the first semipermeable membrane. Although the purge gas is supplied to the gas phase dehumidifier 17, it is clear that there is no need to explain that this purge gas is not limited to air. The first and second semipermeable membrane vapor phase dehumidifiers 17 and 23, the second pump 22, the needle valves 25 and 27, and the conduits 21, 24, 2
6 and 28; 34 supplies the dry measurement gas to the reference electrode 12; This is a comparative gas supply mechanism consisting of a conduit 20 and a gas injection tube.

As described above, the measurement gas 1 is sucked by the pump 16, passes through the filter 9, and then flows into the gas reservoir chamber 8. If the internal volume of the gas reservoir chamber 8 is too large, the time required to replace the measurement gas will increase, the responsiveness to changes in moisture concentration will decrease, and the amount of measurement gas sucked will increase, causing the porous filter 9
This causes problems in handling, such as an increase in the amount of drainage. Therefore, the gas reservoir chamber 8 according to the present invention has an inner diameter D as shown in FIG.
is approximately 35 mm, the length l is approximately 70 mm, and the internal volume is approximately 70 c.c. Furthermore, at least one pore 6 provided in the cover 7 is so small that it does not cause clogging. Therefore, the suction capacity of the pump 16 for one minute is approximately 200 c.c.
Although it is only about 1 minute, it is possible to select the gas replacement time in the gas reservoir chamber 8 to be about 1 minute.
By providing such a gas reservoir chamber 8 outside of the zirconia element 10, short-term fluctuations in the concentration of oxygen contained in the measurement gas are prevented from occurring within the gas reservoir chamber 8 due to the tank action of this gas reservoir chamber. As a result, the electrode contact time of the measuring gas that directly contacts the measuring electrode 11 and the electrode contact time of the measuring gas that contacts the reference electrode 12 after being sampled and dried by the gas sampling tube 14 are thus averaged. This allows reliable and stable moisture measurement by ignoring the time lag.

According to the investigation by the present inventors, Figures 1 to 3
Moisture measuring device 24 equipped with the gas reservoir chamber 8 shown in the figure
When installed on the furnace wall 2 of various drying ovens, it is possible to suppress fluctuations in the oxygen concentration in the gas reservoir chamber 8 to about 2.5% per minute in response to fluctuations in the oxygen concentration in the drying furnace. Ta. As shown in Figure 4, this
A change in oxygen concentration of about 2.5% results in a water content of about 0.6
It is about %. Therefore, if the full scale of moisture measurement is 30%, the measurement accuracy is 2% (0.6/30).
Therefore, it has sufficient reliability. If such a gas reservoir chamber 8 is not installed, the oxygen concentration will fluctuate by several tens of percent and moisture measurement will be impossible, so installing this gas reservoir chamber 8 is extremely effective. Note that the filter 9 shown in FIGS. 1 and 2
is porous and effective in removing dust, but does not have the effect of the gas reservoir chamber 8 to average out fluctuations in oxygen concentration.

Further, in the above embodiment, a semipermeable membrane vapor phase dehumidifier 17 was used to dehumidify the measurement gas. In general, semi-permeable membrane vapor phase dehumidifiers, due to their dehumidification principle, can reduce the area of the semi-permeable membrane in contact with the target gas by lowering the humidity of the purge gas while keeping the dehumidifying capacity constant.
The flow path volume of the gas to be dehumidified can be reduced. In the moisture measuring device 32 described above, the first dehumidifier 17 is a semi-permeable membrane vapor phase dehumidifier, and the purge gas of this dehumidifier is further transferred to the second semi-permeable membrane vapor phase dehumidifier 2.
3, and in the second dehumidifier 23, for example, by increasing the length of the inner tube, sufficiently low-humidity air is supplied to the first dehumidifier 17 as a purge gas, so that the first dehumidifier 17 The measurement gas flow path volume of the device 17 is extremely small, for example, 0.6 ml. Therefore, such a first dehumidifier 1
In the moisture measuring device 32 equipped with 7, the pipes 18, 1
Coupled with the fact that the internal volumes of 9 and 20 are formed small, the time from when the measurement gas is sampled from the end 14a of the gas sampling tube 14 until the dry gas reaches the comparison electrode 12 is extremely short. Even if a concentration fluctuation occurs in the oxygen contained in the measurement gas within a short period of time, the measurement error caused by this concentration fluctuation is extremely small in the moisture measuring device 32.

Note that, as described above, the shorter the residence time of the gas (comparison gas) in the first semipermeable membrane dehumidifier 17, the better, so the inner tube is formed to be short. On the other hand, experiments have confirmed that in order to obtain the desired degree of dryness for the gas flowing inside the inner tube, it is necessary to flow 1.5 times or more of the drying gas compared to the comparative gas flow rate inside the inner tube. . Therefore, in an embodiment of the present invention, the first semipermeable membrane dehumidifier 17
When the same diameter is used for the inner tube of the second semipermeable membrane dehumidifier 23 and the inner tube of the second semipermeable membrane dehumidifier 23, the latter inner tube is formed to be 1.5 times or more longer than the former inner tube. Moreover,
The second semipermeable membrane dehumidifier 23 is made longer because it must also produce its own drying gas.
For this reason, the second dehumidifier 23 is formed longer than the first dehumidifier 17.

〔Effect of the invention〕

As described above, in the present invention, a moisture measuring device that measures the water vapor concentration in a measurement gas using a solid electrolyte oxygen concentration detector is provided with a gas reservoir chamber into which the measurement gas flows through the pores, and a gas reservoir chamber on both sides. A solid electrolyte type oxygen concentration detection device that has a solid electrolyte element provided with a measurement electrode and a comparison electrode in each of the gas reservoir chambers, and is arranged in the gas reservoir chamber so that the measurement gas flowing into the gas reservoir chamber comes into contact with the measurement electrodes. and a comparison gas supply mechanism that collects the measurement gas in the gas reservoir, dries it with a dehumidifier, and supplies it to the comparison electrode section of the oxygen concentration detector, and further includes the dehumidifier with the first and Consisting of a second semipermeable membrane vapor phase dehumidifier and a pump,
This pump supplies a source gas such as air to the second semi-permeable membrane vapor phase dehumidifier to obtain a dried purge gas from this source gas, and allows the measurement gas to flow through the first semi-permeable membrane vapor phase dehumidifier. Since the measurement gas is dried by supplying purge gas, in such a moisture measuring device, fluctuations in the oxygen concentration in the measurement gas outside the gas reservoir chamber within a relatively short period of time are caused by the tank action in the gas reservoir chamber. As a result, the time when the measurement gas contacts the measurement electrode of the oxygen concentration detector and the time when the measurement gas is dried by the comparison gas supply mechanism and the sensor is This has the effect of extremely reducing the error in moisture measurement due to the time lag between the time of contact with the reference electrode and the length of the inner tube of the second semipermeable membrane vapor phase dehumidifier. By improving the dehumidification capacity of the dehumidifier, the flow path volume of the measurement gas in the first semipermeable membrane vapor phase dehumidifier can be reduced, and as a result, the flow time of the measurement gas flowing through the comparison gas supply mechanism is shortened. As a result, as in the case described above, the measurement error due to the time lag between the time when the measurement gas contacts the measurement electrode and the time when the measurement gas is dehumidified and contacts the comparison electrode is effectively reduced.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of an embodiment of the moisture measuring device according to the present invention, Fig. 2 is a diagram explaining the principle of Fig. 1, and Fig. 3 is a schematic diagram of the gas reservoir chamber in Figs. 1 and 2. FIG. 4A is a front cross-sectional view, FIG. B is a cross-sectional view taken along line AA in FIG. A, and FIG. 4 is a moisture measurement characteristic diagram using the gas reservoir chamber in FIG. DESCRIPTION OF SYMBOLS 1... Measuring gas, 6... Pore, 8... Gas storage chamber, 10... Zirconia element as a solid electrolyte element, 11... Measuring electrode, 12... Comparative electrode, 1
3... Oxygen concentration detector, 17... First semipermeable membrane vapor phase dehumidifier, 22... Pump, 23... Second semipermeable membrane vapor phase dehumidifier, 32... Moisture measuring device, 33... Dehumidification Apparatus, 34... Comparison gas supply mechanism.

Claims (1)

[Claims] 1. A solid electrolyte element that is disposed in an atmosphere of a measurement gas containing oxygen and water vapor, and has a gas reservoir chamber having at least one pore into which the measurement gas can flow, and a measurement electrode and a comparison electrode on both sides, respectively. a solid electrolyte oxygen concentration detector disposed within the gas reservoir so that the measurement gas flowing into the gas reservoir comes into contact with the measurement electrode;
a comparison gas supply mechanism that sucks the measurement gas in the gas reservoir, removes the water vapor in the measurement gas with a dehumidifying device, and supplies it as a comparison gas to the comparison electrode section of the solid electrolyte oxygen concentration detector; a first semipermeable membrane vapor phase dehumidifier that dehumidifies the dehumidifying device by causing the measurement gas to flow therethrough; and a first semipermeable membrane vapor phase dehumidifier that is supplied with source gas and dehumidifies the source gas. a second semipermeable membrane vapor phase dehumidifier that supplies purge gas to the dehumidifier, and a pump that supplies the source gas to the second semipermeable membrane vapor phase dehumidifier, and the solid electrolyte oxygen concentration detector A moisture measuring device, characterized in that it measures the concentration of the water vapor in a measurement gas.