JPH0240530A - Crystal oscillation moisture meter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a crystal oscillation type moisture meter. More specifically, the present invention relates to a moisture meter that measures the moisture concentration in the atmosphere using a humidity measurement cell incorporating a crystal oscillation type sensor.

(b) Conventional technology A crystal oscillation type moisture meter that can measure trace moisture concentration in the atmosphere using a crystal oscillation type sensor has a switching connection from the sample gas (wet gas) supply section to the first flow rate control section and the exhaust flow path. a sample gas supply flow path that is extended in this order through a first three-way solenoid valve that can be connected to the humidity measurement cell with a built-in crystal oscillation sensor; and the sample gas supply section of the supply flow path and a first flow rate control A zero gas (dry gas) generation section having a drying section, a second flow rate control section, and a second three-way solenoid valve that can be switched and connected to the exhaust flow path are connected in this order via a pipe. A dry gas supply flow path extending to the humidity measurement cell is known. In the crystal oscillation type moisture meter having the above configuration, the moisture concentration in the wet gas is measured by switching the first three-way solenoid valve and the second three-way solenoid valve to introduce the wet gas or dry gas to be measured into the humidity measurement cell. For example, as shown in Figure 5, dry gas is introduced for 2 minutes and 30 seconds (O mark), and wet gas is introduced for 30 seconds.
Repeat the cycle of alternately introducing each gas for a certain period of time (marked with ◎), and measure the oscillation frequency of the cell once for 1 second just before each gas is switched and introduced. Frequency F0-11+FDfnl, , , and Fw+n-+++ Fw+n+1. , (Oscillation frequency due to Fo Ni dry gas, Fw: oscillation frequency due to wet gas), and the water concentration in the wet gas is calculated based on the difference (ΔF) between these oscillation frequencies.

(c) Problems to be solved by the invention However, in the calculation method based on the above measurements,
A problem arises when measuring very low concentrations of moisture. That is,
In the above measurement once per second, noise in the electric circuit,
The sensor's own noise (oscillation frequency fluctuation) caused by minute water concentration, noise from gas flow inside the cell, etc. cannot be ignored and increases measurement errors, and the difference between dry gas and wet gas Since the frequency difference is small and its change is easy, measurements must be taken at locations where the cell has not reached a steady state due to the introduced gas (i.e., locations where the rate of frequency change is large), which can increase measurement errors. Become.

The present invention was made in view of this situation, and it is an object of the present invention to provide a crystal oscillation type moisture meter that can be used to measure ultra-low water concentrations.

(d) Means for Solving the Problems Thus, according to the present invention, a dehumidified dry gas and a wet gas to be measured are alternately introduced into the humidity measuring cell with a built-in crystal oscillation sensor for a predetermined period of time. ,
In a crystal oscillation type moisture meter configured to measure the moisture concentration of the wet gas based on the frequency difference between the oscillations of the sensor, the oscillation frequency of the sensor due to each introduced gas is changed several times just before switching and introducing the gas into the cell. a storage unit that stores the average oscillation frequency for each introduced gas obtained by measuring and averaging them; and a comparison unit that can calculate the moisture concentration in the wet gas based on the difference between these stored average oscillation frequencies. A crystal oscillation type moisture meter comprising a calculation section is provided.

The present invention is characterized in that the average value of the frequency is obtained from several one-second measurements immediately before the switching and introduction of each gas, and calculation processing is performed based on this average oscillation frequency.

By using the above-mentioned average oscillation frequency, the moisture meter of this invention can reduce the influence of the sensor's own noise (frequency fluctuation), and can set a longer switching interval than conventional ones, making measurements in steady state possible. Therefore, 0. O5ppm.

It can be used to measure moisture at extremely low concentrations, such as H7○.

The storage unit and comparison/calculation unit included in the moisture meter of the present invention can store a preset calibration curve, store each measured value for each measurement, and calculate the average after a predetermined number of measurements. It has a writable/readable memory section so that the calculated average value can be read out and the calculated average value can be stored, and the average value calculation can be performed and the magnitude of the average calculation value can be compared. Based on the output of the comparison result. , and a comparison/calculation section capable of outputting a concentration value corresponding to a stored calibration curve.

In the moisture meter of the present invention, except for configuring the calculation section to enable the above-mentioned calculations, the humidity measurement cell with a built-in crystal oscillation type sensor and the flow path system that constitute the moisture meter may be those known in the art as they are. Can be done. That is, the crystal oscillation type sensor set in the humidity measurement cell is similar to a normal crystal oscillation type humidity sensor. The dry gas supply channel and the wet gas supply channel are constructed in the same manner as in a normal crystal oscillation type moisture meter. The flow rate controller and three-way valve provided in the flow path system are preferably a normal flow rate regulator and three-way solenoid valve. Further, it is preferable that a normal dehumidifying means (dryer) is provided in the dry gas supply channel. Further, the dry gas supply section may be set independently, or may be set in common with the sample gas supply section. In this case, a wet gas supply channel extending from the wet gas supply section is configured to branch, the branch channel is connected to the dehumidifying means, and a dry gas supply channel is further extended from the dehumidifying means. configured to do so.

The moisture meter of this invention switches the flow path and performs measurement according to a predetermined sea fence, processes the obtained measured values based on a predetermined process, and controls the storage section and the comparison/calculation section. A control unit is provided to perform the control. This control section includes
Preferably, it has a display section, a recording section, etc.

(E) Effect According to the present invention, in repeating the cycle of switching and introducing dry gas or wet gas into the humidity measuring cell for a predetermined period of time, dry gas is introduced into the humidity measuring cell, and after a predetermined period of time, wet gas is introduced. In the few seconds immediately before switching, the frequency oscillated from the crystal oscillation type sensor in the cell is measured several times for one second, then wet gas is switched into the humidity measurement cell, and after a predetermined period of time, dry gas is In the several seconds immediately before switching to the introduction of , 1-second measurements are similarly performed several times. Several measured values of the dry gas for each such switching introduction cycle are stored, and their average value is calculated and stored again as the average oscillation frequency.

Similarly, the average oscillation frequency of wet gas is also stored. Next, the moisture concentration in the wet gas is calculated based on the difference between the stored average oscillation frequency of the dry gas and the average oscillation frequency of the wet gas.

The present invention will be described in detail below with reference to Examples, but the present invention is not limited thereby.

(F) Embodiment FIG. 1 is an explanatory diagram of the structure of an example of a crystal oscillation type moisture meter of the present invention. In the figure, a crystal oscillation type moisture meter (1) connects a sample gas (wet gas) supply unit (2) to a flow controller (3) and a three-way solenoid valve (4), a crystal oscillation type sensor (5), and a built-in humidity measurement cell (6). ), a wet gas supply channel (a) extending to the gas outlet (11) via the flow meter (10) in this order, and the wet gas supply channel (a)
Wet gas supply section (2) and flow controller (3)
) of the wet gas supply channel (a) through the dryer (7), flow controller (8), and three-way solenoid valve (9) in this order. ) and a dry gas supply channel (b) connected to the confluence section (b) between the humidity measuring cell (6) and the humidity measuring cell (6). The remaining one of the three-way solenoid valves (4) is connected to the bypass (c), and by operating the solenoid valve, the supply of sample gas is switched to the humidity measurement cell (6) side or the bypass (c) side at regular intervals. It is configured so that On the other hand, the remaining three-way solenoid valve (9) is also connected to the bypass (C) through a pipe (d). Further, the dryer (7) is filled with a desiccant, and the desiccant removes moisture in the wet gas to generate dry gas.

The humidity measuring cell (6) of the moisture meter (1) is provided with a control section (12) that performs moisture concentration calculation processing and drives and controls the moisture meter (1) at a predetermined timing. . This control unit (12) has a built-in CPU (13), and this CPU (13) has a storage unit (14),
Comparison section (15), calculation section (16) and clock (17)
) are connected to each other. Note that a flow path to a drain (not shown) is set in the cell.

The operation of the control section (12) of the crystal oscillation type moisture meter (1) configured as described above will be explained.

(i) About driving By switching and setting the three-way solenoid valve in the moisture meter (1) to the bypass side, wet gas is transferred from the wet gas supply section → flow controller (3) → three-way solenoid valve (4) - bypass. On the other hand, a part of the wet gas is transferred from the wet gas supply channel in the order of branch section - dryer -> flow controller (8) -> three-way solenoid valve (9) - confluence section - humidity measurement cell, and then from the cell to the drain. is being released into the river. With the above configuration, dry gas is always in contact with the crystal oscillation type sensor, but during measurement, the three-way solenoid valve (4) is switched and the wet gas supply section - flow controller (3) - three-way solenoid valve (4) - A wet gas supply channel is configured to connect the humidity measurement cells in this order. In the measurement, the above switching is set by the clock (17) so that one cycle consists of dry gas introduction for 4 minutes and 30 seconds and wet gas introduction for 1 minute and 30 seconds, and according to this, the crystal oscillation type sensor ( 5), frequency fluctuations occur in the pattern shown in FIG.

(ii) Regarding 0 degree calculation, using the frequency fluctuation pattern shown in Figure 2 as an example,
The explanation will be based on the calculation method shown in the figure. Here, in general, F: Frequency F v (rB) obtained by measuring 1 second immediately before switching to wet gas at the time of introducing dry gas in the nth cycle, Frequency obtained by measuring 1 second just before switching to dry gas.

For the measurement of each F D+nl, Fw, several seconds immediately before introducing switching (D
W n-+ +D, , corresponds to Wn) five times (indicated by * in the figure). (In addition, in the diagram, O
The mark indicates dry gas introduction, and the ◎ mark indicates wet gas introduction. ) That is, at the point Ri,, the five oscillation frequencies Fo(.,)
.

F Dfntl l F o, n++ + F o+n
++ + F o+ns+ is measured and stored.

Similarly, 5 in Dn-++ Wl'l-1+ wn
Steps 1 to 3 in Figure 3 are measured and stored (Fig. 3).
reference).

Next, the average value of the five memorized measured values is calculated in the arithmetic unit, and this average oscillation frequency: FD is stored. The average is calculated in the same way for each measurement point, and F D
fn-11+F Win-11+F Wfrt+ is stored (steps 4 to 9 in FIG. 3).

Next, each memorized average oscillation frequency is determined by the frequency difference (
ΔF) is calculated. That is, the difference in frequency at the time of dry gas introduction in the n-th cycle: 8 FD) is 8 F o+-+=Fw+. -++ (3/4XFo+
n-1,"l/4XFo+n+) (Step 10 in Figure 3
) ・Difference in frequency when introducing wet gas in the nth cycle: ΔFw (. is 8F Win+ = (3/4XFw+n+”l/4X
Fw+n-++) Fo+n+(Figure 3 Step 11
) Based on the calculated frequency difference (ΔF), the moisture concentration is finally calculated based on the calibration curve stored in the storage section, and the result is displayed on the display section. A similar calculation process is performed for each cycle to determine the concentration.

Incidentally, FIG. 4 shows the indicated noise levels obtained in the above cycle with and without averaging calculation (corresponding to steps 4 to 9 above). From this figure, it can be seen that the moisture meter of the present invention having the above calculation method can suppress the noise level to about half of the conventional one. Therefore 0. It can be seen that it can be used to measure ultra-low water concentrations such as O5ppm, H, and O.

(g) Effects of the Invention According to the present invention, the noise level can be reduced to about 0.01 ppm, so it can be used for measuring ultra-low water concentrations, such as measuring water in semiconductor manufacturing gases.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of an embodiment of a crystal oscillation moisture meter according to the present invention, FIG. 2 is a schematic diagram showing a pattern of frequency fluctuation by the moisture meter of FIG. 1, and FIG. 3 is a diagram similar to that of FIG. 1. A flowchart diagram explaining the steps of concentration calculation using a moisture meter,
FIG. 4 is a graph showing the noise level of the moisture meter of the present invention together with a comparative example, and FIG. 5 is a schematic diagram showing the pattern of frequency fluctuation based on the measurement cycle of the conventional example. (2)...Wet gas supply section, (3),
(8)...Flow controller, (4), (9
)...Three-way solenoid valve, (5)...Crystal oscillation type sensor, (6)...Fill/humidity measurement cell, (7
)...Dryer, (10)...Flowmeter, (11)...Gas outlet, (12)...
...control unit, (13) ...CPU
. (14)...Storage section, (15)...
... Comparison section, (16) ... Calculation section, (1
7) Clock, (a) Wet gas supply channel, (b) Dry gas supply channel, (c) Bypass , (d)...
...Connecting pipe, 8g Cabinet diagram diagram diagram diagram

Claims (1)

[Claims] 1. A dehumidified dry gas and a wet gas to be measured are alternately introduced into a humidity measuring cell with a built-in crystal oscillation sensor for a predetermined period of time, and the frequency difference between the oscillations of the sensor is adjusted. In the crystal oscillation type moisture meter configured to measure the moisture concentration of the wet gas based on the above, the oscillation frequency of the sensor due to each introduced gas is measured several times just before switching to the cell, and the measurements are averaged. a storage unit that stores the average oscillation frequency for each introduced gas obtained by the above-described method; and a comparison unit that can calculate the moisture concentration in the wet gas based on the difference between these stored average oscillation frequencies.
A crystal oscillation type moisture meter equipped with a calculation section.