JPS62254046A - Determination of dry ending point - Google Patents

Abstract

PURPOSE:To determine the dry ending point of an object to be dried, by measuring a plate current (IP) of a high frequency oscillation tube for heating the object being dried at each fixed time to obtain a difference between the preceding IP measured value and the current IP measured value when the resulting value is below a fixed value. CONSTITUTION:A plate voltage is applied to a high frequency oscillation tube TU to start high frequency oscillation and an oscillation output thereof is applied to electrode plates 1 and 2 through a coupling circuit 25 to perform a high frequency induction heating of an object 3 to be dried. As the water content of the object 3 being dried lowers, the decreasing current IP of the oscillation tube TU is measured at each fixed time and a difference is determined between the preceding current IP measured value and this current IP measured value when the resulting value is below a fixed value. Thus, the dry ending point is given at the point of time at which the difference becomes smaller than a preset value. In other words, the time at which the decrease per a fixed time of the water content of the object 3 being dried falls below a fixed value is determined to be the dry ending point and hence this enables the ending of drying when the water content of the object being dried reaches a low level close to an equilibrium water content previously obtained for material thereof.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is applicable to, for example, fiber B (spin-rolled cheese, i!II!
thread.

The present invention relates to a method for determining the drying end point for determining the drying end point when drying a single product 8) to a predetermined moisture content at 10 j frequency.

[Conventional technology]

As a method for determining the drying end point when high-frequency drying (high-frequency dielectric heating) is applied to a material to be dried, for example, Japanese Patent Publication No. 59-5
A method disclosed in Japanese Patent No. 3392 is known. The method for determining the drying end point is to cool the water vapor evaporated by high-frequency drying, measure the amount of water, and determine the drying end point when the amount of water reaches a predetermined amount.

In addition to this, dry S! There is also a method in which the IT of the object is measured and the point at which the decrease from the start of drying @9 reaches a predetermined value is set as the drying end point.

[Problem that the invention seeks to solve]

The conventional method for determining the drying end point described above is based on the method of determining the drying end point. A or ill is detected, and the drying end point is determined when the volume or lit of this water reaches a predetermined setting (^), and the initial ff1 of the material to be dried is
T! However, there is a problem in that the moisture content of the material to be dried at the end of drying varies greatly due to variations in the initial moisture content.

An object of the present invention is to provide a method for determining a drying end point that can reduce variations in the moisture content of a material to be dried at the drying end point.

[Means for solving problems]

The drying end point determining method of the present invention is a drying end point determining method for determining the drying end point when a material to be dried is subjected to high frequency dielectric heating and high frequency drying, the drying end point being determined by a high frequency salt generating tube for high frequency dielectric heating. The plate current is measured at regular intervals, and when the value falls below a predetermined value, the difference between the previous plate current measurement and the current plate current measurement is calculated, and the difference is determined in advance. The point in time when the setting becomes smaller than the set value 1 is defined as the drying end point.

[Effect]

According to this invention, the plate current of the high I4 wave oscillator tube, which decreases as the moisture content of the material to be dried decreases, is measured at regular intervals, and the previous plate current measurement value and the current plate current judgment value are combined. The drying end point is determined when the ax becomes smaller than the set value, so when the amount of decrease in the plate current per fixed time becomes less than the predetermined value, that is, when the moisture content of the material to be dried is constant. High frequency drying can be stopped when the amount of decrease per hour becomes less than a predetermined value and the moisture content becomes low, close to the 41 equilibrium moisture content of the atmosphere. The variation in moisture content can be reduced.

Moreover, the equilibrium moisture content of the material to be dried varies depending on the material, but the end point of drying is when the amount of decrease in the moisture content of the material to be dried per a certain period of time becomes less than a predetermined value. Regardless of the material of the object to be dried, drying can be terminated when the moisture content reaches a low level close to the equilibrium moisture content of the material.

〔Example〕

An embodiment of a high frequency drying apparatus for determining the C drying end point using the drying end point determining method of the present invention will be described with reference to FIGS. 1 to 7. This high frequency drying device
As shown in Figures 1 and 2, there is a drying chamber 4 in which a pair of electrode plates 1.2 are spaced apart and a material to be dried 3 can be inserted between them, and a drying chamber 4 is provided at an external position of this drying chamber 4. a pressure reducing means 5 for reducing the pressure inside the drying chamber 4; and a material to be dried 3 in the drying chamber 4.
and a heating means 6 for applying high frequency voltage to the material to be dried by high frequency dielectric heating.

The drying chamber 4 is equipped with an opening/closing door 7 that seals the interior of the chamber, and a trolley 8 on which the material to be dried 3 is placed and inserted into the electrode plate 1.2.
is set up so that it can be transported.

The pressure reducing means 5 connects a vacuum pump 9 that reduces the pressure inside the drying chamber 4 to the drying chamber 4 via an automatic valve 10, and
A pressure regulator 11 for controlling the pressure inside the drying chamber 4 is provided. An automatic drainage valve I2 is provided below the drying chamber 4 for discharging condensate generated by heating the material 3 to be dried and emitting moisture.

The heating means 6 includes a high frequency oscillator 1 located outside the drying chamber 4.
4, and the high frequency output from the high frequency salt generating tube wi14 is sent to the electric bridge 16 in the drying room 4 via the cable 15.
．． 1? It is further guided from the electrodes 16° 17 to the electrode plates 1.2 provided above and below or on both sides of the object 3 to be dried, so that the object 3 to be dried is heated by high frequency dielectric. The operation of the high frequency oscillator 14 is controlled by the control device 18.

As shown in FIG. 3, the ini frequency oscillator 14 is connected to a power supply circuit 21, and! ! A flow circuit 22, a filter circuit 23,
It is composed of an oscillation circuit 24 and a coupling circuit Ws25.

The power supply circuit 21 includes a step-up transformer TR1 that externally boosts the voltage of the three-phase Shokawa power supply to approximately 10 V, a power switch SW provided on the primary side of the step-up transformer TR, and single contactors MC, MC2. Contact mcl.

mC2.

The rectifier circuit 22 is composed of six diodes D, ~[)6.

The filter circuit 23 is inserted for the purpose of preventing the high frequency waves from the oscillation circuit 24 from flowing out to the power supply circuit 21, and the filter circuit 23 is inserted in order to prevent the high frequency waves from the oscillation circuit 24 from flowing out to the power supply circuit 21. It consists of capacitors c, , c2° and resistors R,.

The oscillation circuit 24 is connected to the rectifier circuit 2 via the filter circuit 23.
High frequency 9. plate connected to 2. 1, C tuning circuit TK connected to the live pipe TtJ and the plate of this high frequency salt generating pipe '1゛U via a capacitor C3 for stopping DC 1q1.
, a grid circuit GR connected to the grid of the high-frequency oscillation tube 'rU, and a filament transformer TR2 that heats the filament of the high-frequency oscillation tube TU.
・is heated and the contact mcl of the magnetic contactor MCI
When turned on and a plate voltage is applied to the high frequency oscillator tube 1, it oscillates at a frequency of 3 to 30 Mllz, and this high frequency oscillation output is sent to the electrode plate 1.2 through the coupling circuit 25. In addition to the space between the electrode plates 1 and 2, the material to be dried 3
is heated by high frequency dielectric.

The coupling circuit 25 consists of fixed capacitors C4 and C5 and a variable capacitor VC, and the capacitance of the variable capacitor VC can be changed by a motor (not shown), etc., and the moisture content of the material 3 to be dried can be changed by high frequency drying. In order to prevent the plate current from decreasing due to the decrease in dielectric loss due to the decrease in the plate current, I.
P is detected, and in order to keep this plate current IP constant, the capacitance of the variable capacitor VC is increased by a motor or the like, and the coupling between the oscillation circuit 24 and the electrode plate 1.2 is gradually made tighter. It has become. Note that when the water content decreases to a certain extent and the coupling degree of the ζ coupling circuit 25 reaches its maximum, if the water content decreases thereafter, the drying material 3 is out of the current controllable region. The decrease in dielectric loss due to the low water content of G causes the play 1 current IP to decrease.

The curve in Figure 4 is the high frequency oscillator tube 'I' [J
This is a time chart showing changes in the plate currents My and IP, and the section A-13 is the plate current controllable region, and its value is controlled by IPA.The section after 13 is the plate current controllable region. In this region, the plate current IP decreases as the water content decreases.

As shown in FIGS. 3 and 5, the control device 18 includes a resistor R that detects the plate current IP of the high frequency oscillation tube TLJ.
2, and a filter 2 for removing high-frequency waves from the voltage across the resistor R2.
6, and a sample/hold circuit S H that samples and holds the output of the amplifier AP.
and an analog-to-digital converter A11) that converts the output of the sample-and-hold circuit SH from analog to digital.
It is composed of a timer TM, a notification iHc, and a central processing unit CPLI. In addition, in FIG. 5, the filter 26
illustration is omitted.

This control device 18 is for determining the drying end point when performing high-frequency dielectric heating on the drying object 3 and high-frequency drying the drying object 3, and controls the plate of the high-frequency oscillation tube TU for high-frequency dielectric heating. The current IP is measured at regular intervals, and when the value falls below a predetermined set value 1p, the difference between the previous plate current measurement value IPY and the current plate current measurement value ipx is calculated. ΔIP is determined, and the point in time when the difference ΔIP becomes smaller than a preset value ΔIPR is determined to be the end of drying, the high frequency oscillation is stopped, and the end of drying is notified.

Here, the central processing unit CP t in the Ya control device 18
The operation of J will be explained in detail with reference to the flowcharts of FIGS. 6 and 7.

First, as shown in Fig. 6, the previous plate current measurement value IPY is initialized, and the set value IPC of the plate current at which the determination of the difference △1F· should be started and the set value IPR of the difference are set. (step x 1).

Next, step
), wait for a certain period of time (step Start drying.

Next, start the timer TM+! :(Sute, Bu X5
), the timer TM generates a pulse at fixed time intervals T.

Then, the timer TM is started, and every time a pulse is input from the timer TM to the central processing unit cPU, the interrupt processing shown in the flowchart of FIG. 7 is performed.

In this interrupt processing, the central processing unit CP1. . ! Input the measured value IPX of the current play 1 ~ current that is output from the device (Stennob Y+).

Next, it is determined whether the current measured value IPX of the plate current is smaller than the set value IPC of the plate current (step Y2), and if the determination result is NO, the process ends.

On the other hand, if the judgment result is YES, calculate ΔIP-IPY-'lPX and calculate IP to the difference between the previous plate current measurement value IPY and the current plate current measurement hI'l'I PX. (Step Y3).

Next, determine whether the difference △lP is smaller than IPR to the set value of the difference (step Y4), and if the result is NO, set the current measured value of the plate current as IPY"IPX!1 'X is the previous plate current measurement value IPY, step y5), and the process is completed this winter.

On the other hand, when the above judgment result is YtlKS, the excitation of the electromagnetic contactors MCI and MC2 is stopped, the high frequency oscillation is stopped, and the high frequency drying is ended (sprag Y[;
) *Next, the alarm HC makes a notification that the drying has been completed (step Y7).

Next, the timer TM is stopped and the process ends (step Ys). With this configuration, as shown in Fig. 4), the Schiller l-current 11 is applied every hour after the start of high-frequency drying. This measured value IPX is compared with the set value 1r (:
Only when the measured value 111 △l I) When the difference I T= becomes smaller than the set value △IP11, for example at point H in Fig. 4, the excitation of the electromagnetic contact ziM(-1°MC2 is stopped and the high frequency When the oscillation stops and the high frequency drying of the object 3 to be dried ends, the notification circuit HC notifies that the drying has ended.

In addition, before the above-described high frequency drying operation, the material to be dried 3 is placed on a trolley 8 and carried into the drying chamber 4, inserted between the electrode plates 1 and 2, and the door 7 is closed to seal the drying chamber 4. Next, it is necessary to operate the vacuum pump 9 to reduce the pressure inside the drying chamber 4.

In addition, after drying is completed, the automatic valve 13 is operated to dry the drying chamber 4.
Air is introduced into the container, the door 7 is opened, and the dried material 3 is taken out.

According to this embodiment, the flow ip of the plate 11 of the high frequency oscillation tube TU decreases as the moisture content of the material to be dried 3 decreases.
is measured every r11 times, and plate fiiI is measured n1 times.
Measured value of L IPY and measured value of current play 1 current IPX
The difference △IP from In other words, when the amount of decrease in the moisture content of the material to be dried 3 per certain period of time becomes less than a predetermined value, and the moisture content reaches a low moisture content close to the equilibrium moisture content in the atmosphere, the high frequency drying is stopped (
- The amount of decrease in the moisture content of the dried material 3 per certain period of time is completely unaffected by fluctuations in the initial weight of the dried material 3 and variations in the initial moisture content, and the amount of decrease in the moisture content of the dried material 3 at the drying end point is Variations in the moisture content of product 3 can be reduced.

Moreover, although the equilibrium moisture content of the material to be dried 3 varies depending on its material, even when the amount of decrease in the moisture content of the material to be dried 3 within a certain period of time becomes less than a predetermined value.

Since this is set as the drying end point, regardless of the key quality of the material to be dried 3, it is possible to end the special number J drying when the moisture content is low, close to the equilibrium moisture content of the material.

Note that in the above embodiments, drying is performed under reduced pressure at °C, but depending on the type of the material to be dried 3, it may be dried under atmospheric conditions, and the temperature is not limited to the pressure inside the drying chamber 4. .

Further, in the above embodiment, fibers were explained as an example of the material to be dried 30'), but the material to be dried 3 is not limited to this.
It may be made of ceramic products such as ceramics, or wood such as veneer.

〔Effect of the invention〕

According to the method of determining the drying end point θ of this invention, the plate current of the high frequency oscillator tube, which decreases as the moisture content of the material to be dried decreases, is measured at regular intervals, and the measured value of the previous plate current and the current value are Find the difference between the measured value of the plate current and
The drying end point is defined as the point when this difference becomes smaller than the set value, so when the amount of decrease in the plate current per fixed time becomes less than the predetermined value, that is, the amount of decrease in the moisture content of the material to be dried per fixed time. High-frequency drying can be stopped when the moisture content in the atmosphere is below a predetermined value and the moisture content is close to the equilibrium moisture content in the atmosphere, reducing the variation in the moisture content of the material to be dried at the drying end point. can.

Furthermore, although the equilibrium moisture content of the material to be dried varies depending on its material, the drying end point is set when the amount of decrease in the moisture content of the material to be dried per a certain period of time falls below a predetermined value. Regardless of the material, drying can be terminated when the moisture content reaches a low moisture content close to the equilibrium moisture content of the material.

[Brief explanation of drawings]

Fig. 1 is a schematic side view showing the configuration of a high frequency drying device used in carrying out the present invention, Fig. 2 is a schematic front view of Fig. 1 with the door open, and Fig. 3 is a circuit of the high frequency oscillation device. Figure 4 shows the plate Ti? of the high frequency oscillation tube. Fig. 5 is a block diagram of the control bag; Figs. 6 and 7 are flow charts showing the operation of the control device. 3... Material to be dried, TIJ...・High-frequency oscillator tube patent applicant: Kanebo Co., Ltd., Ba Co., Ltd.] 1 Manufacturing Company

Claims (1)

[Claims] A method for determining a drying end point when a material to be dried is subjected to high frequency dielectric heating for high frequency drying, the method comprising: determining a drying end point for determining a drying end point when a material to be dried is subjected to high frequency dielectric heating and high frequency drying, the method comprising: When the value falls below a predetermined value, the difference between the previous plate current measurement value and the current plate current measurement value is calculated, and the difference is smaller than the preset value. A method for determining a drying end point in which the point at which the drying end point is reached is determined as the drying end point.