JP2009244223A - Moisture measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a moisture percentage measuring method and a moisture measuring system that are capable of calculating a moisture percentage by precisely measuring the value of a current even if the current is a noisy output current. <P>SOLUTION: A moisture measuring method for calculating the water content of an analyte by using a moisture percentage measuring instrument 1 having at least a pair of a cathode and an anode fixed at an interval of 1 mm or shorter, immersing the cathode and the anode in the analyte, and then measuring the electrolytic current of water between the electrodes by applying predetermined alternate voltages to both the electrodes for each cycle includes steps of: applying alternating, rectangular-wave, or triangular-wave voltages to both the electrodes; taking out the output current value of a cyclic component based on the applied alternating voltage from a spectrum obtained by the frequency conversion of an output current-time output signal; and calculating the water content of the analyte from the output current value which is thus taken out. Moreover, the moisture measuring system includes a moisture measuring instrument 1, a measuring section 2 for measuring the electrolytic current of water; an analyzing section 3 for determining the water content, an output section 4, and a display section 5. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a moisture measuring method, and more particularly, to a moisture measuring method and a moisture measuring system that can quantify moisture easily and accurately even in a specimen that easily generates noise using an electrochemical method.

  Conventionally, the Karl Fischer method is known as an electrochemical method for moisture measurement. This method is suitable for the measurement of trace moisture, and is a coulometric titration method using a Karl Fischer reagent. It can be used for absolute determination of trace moisture in a few minutes, so it is widely used as a batch-type desktop analyzer. is doing.

  However, the Karl Fischer method uses expensive reagents, which increases the cost of analysis, and complicates the equipment, leading to higher equipment costs and increased equipment maintenance costs. not being used.

  As an on-line type moisture measurement method, an infrared absorption method, a dielectric method, a conductivity method, an ultrasonic method, a thermal conductivity method, and the like are known.

  However, since the infrared absorption method measures the amount of reflection of near infrared rays, errors are likely to occur unless the sample surface is flat, and it is difficult to apply it to the measurement of dark samples. Since the dielectric constant or dielectric loss is measured, there is a problem that sufficient quantitative properties can be obtained only when the water content is in the range of about 0 to 50%. In addition, since the conductivity method is affected by changes in conductivity and pH due to organic acids and carbon dioxide, the measurement accuracy is lowered depending on the measurement environment (Patent Document 1). In particular, the conductivity method measures AC impedance, etc., so that there is no change in pH of the sample, and the ultrasonic method measures the amount of ultrasonic energy attenuation, so it is a homogeneous sample without bubbles, etc., thermal conductivity Since the method measures temperature changes due to heat pulses, it is required to be homogeneous data without bubbles, etc., so it is necessary to adjust the sample, and it is used only in a limited area as a general industrial instrument. This is the current situation.

  For specimens with high water content, the dry weight method is exclusively used. The dry weight method is a time-consuming measurement method and is never easy to automate, because the sample weight is measured and then dried and the dry weight is measured to determine the water content from the difference in weight. Not.

Therefore, the present applicant measures the electrolytic current by a constant voltage electrolysis method using an electrode for a specimen containing moisture, and obtains the moisture content in the specimen based on a calibration curve prepared in advance from the current value. A measuring instrument and a moisture measuring method were proposed previously. In this method in which the movement of electrons due to electrolysis of water depends on the stability of the diffusion layer, the distance between the cathode and the anode is set to 1 mm or less in order to improve the measurement accuracy (Patent Document 2). In this method, the moisture content of a wide range of specimens of about 0 to 90% can be easily measured.
JP, 2004-294448, A Capacitance type moisture sensor Japanese Patent Publication No. 7-69300

  However, the present inventors have found that there are still problems to be solved.

  If the distance between the cathode and anode is 1 mm or less, the movement of electrons increases the degree of freedom to some extent, so the accuracy increases. However, when measuring the moisture content of static sludge, the output current (measurement current) with respect to the input specific voltage ) Appeared and it was difficult to accurately measure the current value.

  For fluid samples, noise appears in the output current in the input process in a certain direction due to the inversion of the input voltage, and even if it is inverted, the noise is output as the output current as a result. It turns out that it lacks sex.

  When noise was observed, it was necessary to repeat the measurement and average the current values.

  Therefore, an object of the present invention is to provide a moisture content measurement method and a moisture measurement system capable of measuring an accurate current value and obtaining a moisture content even when an output current in which noise is observed.

  Other problems of the present invention will become clear from the following description.

  The above problems are solved by the following inventions.

(Claim 1)
Using a moisture measuring device in which at least a pair of cathodes and anodes are fixed at intervals of 1 mm or less,
Moisture measurement method for determining the moisture content in the specimen by immersing the cathode and anode in the specimen and then applying a constant alternating voltage to each of the electrodes every period to measure the electrolysis current of water between the electrodes. In
Apply alternating, rectangular or triangular voltage to both electrodes,
The output current value of the periodic component based on the applied alternating voltage is extracted from the spectrum obtained by frequency conversion (Fourier transform) of the output signal of output current-time,
A method for measuring moisture, characterized in that a moisture content in a specimen is obtained from the output current value taken out.

(Claim 2)
2. The moisture measuring method according to claim 1, wherein at least one pair of the cathode and the anode of the moisture measuring device has only its tip exposed, and its periphery is insulated by a resin.

(Claim 3)
A moisture measuring device having at least one pair of cathode and anode fixed at intervals of 1 mm or less;
After immersing the cathode and anode in a specimen, a measuring unit that measures the electrolysis current of water between the electrodes by applying a constant alternating voltage to each of the electrodes at each cycle;
An analysis unit that takes out an output current value of a periodic component based on an applied alternating voltage from a spectrum obtained by frequency conversion (Fourier transform) of an output signal of output current-time, and determines a moisture content;
An output unit for outputting the determined amount of water;
A moisture measuring system comprising a display unit for displaying the output moisture content.

(Claim 4)
Spectrum obtained by the analysis unit by inputting an output signal of output current-time from the measurement unit, a frequency transform (Fourier transform) unit, and a spectrum obtained by frequency transform (Fourier transform) of the output signal of output current-time A reading unit that reads out and reads out an output current value of a periodic component based on an applied alternating voltage from a reading unit, and a control unit that determines a moisture content by comparing the read out output current value with a calibration curve prepared in advance. Item 4. The moisture measuring system according to item 3.

  According to the method of the present invention, it is possible to provide a moisture content measuring method and a moisture measuring system capable of measuring an accurate current value and obtaining a moisture content even if an output current has noise.

  The on-line instrument for measuring moisture according to the method of the present invention has a wide range of moisture that can be measured and is particularly useful in fields such as the chemical industry, the food industry, and the metal industry because of its simplicity and economy as well as excellent measurement accuracy. is there.

  Embodiments of the present invention will be described below.

  FIG. 1 is a schematic view showing an example of the moisture measuring apparatus of the present invention. This apparatus comprises a moisture measuring device (sensor) 1 having an exposed cathode and anode, a measuring unit 2, an analyzing unit 3, an output unit 4, and a display unit 5.

  The sensor 1 has at least one pair of a cathode and an anode connected to a power source and a measurement unit, respectively, and a resin insulating part that fixes the cathode and the anode and holds the tip part so as to expose only the tip part.

  As a material constituting the cathode and the anode, platinum group elements such as Ru (ruthenium), Rh (rhodium), Os (osmium), Ir (iridium), Pt (platinum), and particularly Pt are preferably used. Metals such as technetium), Ag (silver), Cd (cadmium), Re (rhenium), and Hg (mercury), or a Ti (titanium) plate coated with Pt, Ru / Pt, or the like can be used.

  In the present invention, the distance between the cathode and the anode is set to 1 mm or less, preferably 0.2 mm or less, more preferably 0.05 to 0.1 mm in order to reduce the influence of the change in the conductivity of the specimen.

  The electrode width of the cathode and / or anode is 1 mm or less, preferably in the range of 0.2 to 0.5 mm from the point of preventing the oxygen gas and hydrogen gas generated during electrolysis from stagnating on the electrode surface and generating noise. It is said.

  At least one pair of the cathode and the anode may be used, but the cathode and the anode may be alternately arranged and used as a comb-type electrode. The length of the exposed electrode is not particularly limited, but the longer the electrode length, the larger the electrolysis current value can be obtained and the influence of noise can be reduced. In the case of a comb-type electrode, the same effect can be obtained by increasing the number of electrodes.

  Reference numerals 11 and 12 denote lead wires connected to the anode and the cathode, respectively.

  When measuring moisture, the sensor 1 is immersed in the specimen.

  The measurement unit 2 is measured by a power source unit 21 that applies a voltage higher than the electrolysis voltage of water, preferably a voltage of 2.5 V or higher, an electrolysis current measurement unit 22 that measures an electrolysis current, and an electrolysis current measurement unit 22. The current value output unit 23 outputs the current value.

  Applying a voltage of 2.5 V or more means that the difference between the anode potential and the cathode potential is 2.5 V or more as shown in FIG.

  The voltage applied to the electrode by the power supply unit 21 is an alternating voltage that reverses the polarity (+, −) at regular intervals from the viewpoint of preventing the formation of an oxide film on the electrode surface and the electrodeposition of various substances on the electrode. To do. By applying the alternating voltage, the decrease in sensitivity in the electrolytic current value is small, and the moisture content can be measured with high accuracy.

  As an application method, a sine wave, a rectangular wave, or a triangular wave may be used as shown in FIGS. 3A, 3B, and 3C. May be.

  The frequency of the alternating voltage is preferably in the range of 0.01 to 1 Hz, more preferably 0.1 to 0.5 Hz.

  When a voltage is applied, water is electrolyzed and a current (Faraday current) flows. This current (constant potential electrolysis, output current) is measured by the electrolysis current measuring unit 22. Since the capacitor current flows immediately after the voltage application, it is preferable to remove the current for 10 to 15 seconds immediately after the application from the measured value.

  The above will be described in more detail. In the case of the same sample, when the electrode interval is wide as 5 to 10 mm instead of the electrode system of the present invention, the capacitor current is larger than the electrolytic current (Faraday current). The ratio of (capacitance current) increases, and as a result, the S / N ratio decreases. In the case of normal dewatered sludge, the Faraday current is 10% or less at an applied voltage of about 4 V, with a signal (current peak) in one cycle when the electrode interval is 5 mm. In this case, highly accurate moisture measurement cannot be performed even by frequency conversion (Fourier transform, FT). On the other hand, when the electrode interval is 0.2 mm, for example, as in the case of the electrode of the present invention, when the rectangular wave voltage of FIG. 3B is input (see FIG. 4A), the electrode of FIG. Such an output signal is obtained.

  In FIG. 4B, the x portion is a capacitor current, and the y portion is a Faraday current. In the present invention, the original electrolytic current is obtained by sampling the FT current output signal of the y portion and performing FT. It is.

  The current value output unit 23 outputs the current value measured by the electrolytic current measurement unit 22 to the analysis unit 3. The measured output current has an unstable waveform (noise) that fluctuates randomly. Since the current value is not stable, the true electrolysis current cannot be known. Therefore, it is necessary to read the true current value by performing FT in the analysis unit 3.

  The analysis unit 3 includes an input unit 31 for inputting the current value output from the current value output unit 23, a Fourier transform unit 32 for decomposing the current value into frequency components, and a current value divided into frequency components by Fourier transform. The reading unit 33 reads the true current value, and the control unit 34 determines the moisture content by comparing the read current value with a calibration curve prepared in advance.

  The current value input to the input unit 31 is decomposed by the Fourier transform unit 32 into frequency components using the Fourier transform, considering the entire region of the measured current value as one period.

  FIG. 5 shows a current value that has been subjected to Fourier transform and decomposed into frequency components. As shown in FIG. 5, the electrolysis current value of water is seen in a region of about 0.7 Hz, and other regions can be distinguished as noise components.

  The reading unit 33 reads the height z of the current value converged in the region of about 0.7 Hz as a true current value.

  In the control unit 34, the moisture content is determined from the current value read by the reading unit 33 based on a calibration curve created in advance.

  The amount of water determined by the control unit 34 can be output from the output unit 4 to the display unit 5 such as a monitor. In addition, the amount of water can be recorded constantly or intermittently in a storage unit (not shown).

  In the moisture measuring method of the present invention, the moisture content is obtained from the electrolysis current value, so that it is not subject to interference by organic acids or carbon dioxide, which is a problem in the conductivity method, etc. On the other hand, correction is necessary.

  Examples of the present invention will be described below, but the present invention is not limited to such examples.

Example 1
Moisture measurement of the dehydrated sludge cake in a stationary state was performed using a sensor moisture meter having a distance between the cathode and the anode of 0.2 mm and 10 pairs.

  As an input voltage, 2.5 V was applied by a continuous rectangular wave in which positive and negative were inverted every 30 seconds.

  When the measured output current was converged by Fourier transform, and a current value in the vicinity of 0.7 Hz was determined, the moisture content was 80.1%.

Comparative Example 1
When the same dewatered sludge cake was measured by the dry weight method, it was 80 to 81%.

The schematic diagram which shows an example of the moisture measuring apparatus of this invention Measurement principle diagram Schematic diagram of input voltage waveform Schematic diagram of square wave applied voltage and output signal The figure which shows the electrolytic current value decomposed into frequency components

Explanation of symbols

1: Sensor 11, 12: Lead wire 2: Measuring unit 21: Power supply unit 22: Electrolytic current measuring unit 23: Current value output unit
3: Analysis unit 31: Input unit 32: Fourier transform unit 33: Reading unit 34: Control unit 4: Output unit 5: Display unit

Claims (4)

Using a moisture measuring device in which at least one pair of cathode and anode is fixed at an interval of 1 mm or less,
Moisture measurement method for determining the moisture content in the specimen by immersing the cathode and anode in the specimen and then applying a constant alternating voltage to each of the electrodes every period to measure the electrolysis current of water between the electrodes. In
Apply alternating, rectangular or triangular voltage to both electrodes,
The output current value of the periodic component based on the applied alternating voltage is extracted from the spectrum obtained by frequency conversion (Fourier transform) of the output signal of output current-time,
A moisture measuring method characterized in that the amount of moisture in a specimen is obtained from the output current value taken out.   2. The moisture measuring method according to claim 1, wherein the moisture measuring device has at least one pair of a cathode and an anode, with only the tip portion exposed, and its periphery insulated by a resin. A moisture measuring device having at least one pair of cathode and anode fixed at intervals of 1 mm or less;
After immersing the cathode and anode in a specimen, a measuring unit that measures the electrolysis current of water between the electrodes by applying a constant alternating voltage to each of the electrodes at each cycle;
An analysis unit that takes out an output current value of a periodic component based on an applied alternating voltage from a spectrum obtained by frequency conversion (Fourier transform) of an output signal of output current-time, and determines a moisture content;
An output unit for outputting the determined amount of water;
A moisture measuring system comprising a display unit for displaying the output moisture content.   Spectrum obtained by the analysis unit by inputting an output current-time output signal from the measurement unit, a frequency transform (Fourier transform) unit, and an output current-time output signal by frequency transform (Fourier transform) A reading unit that reads out and reads out an output current value of a periodic component based on an applied alternating voltage from a reading unit, and a control unit that determines a moisture content by comparing the read out output current value with a calibration curve prepared in advance. Item 4. The moisture measuring system according to item 3.

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