JP2001124613A - Method for measuring level in stirring tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the level in a stirring tank without being restricted on the range of level measurement, measurement accuracy, and responsiveness by stirring blades and to measure the level of a large-capacity stirring tank by means of a radiation source of relatively small capacity in the similar way for a stirring tank without stirring blades. SOLUTION: When the level of the stirring tank 6 for stirring its content by rotary stirring blades is measured by a transmission-type level gauge using attenuation of transmitted radiation, the level measurement is performed based on an output signal of the level gauge during a non-cut-off period when the stirring blades 10 do not cut off the transmitted radiation from the level gauge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the level of a stirring vessel for stirring the contents by a rotating stirring blade, and more particularly to a method for measuring the level of a transmission line by attenuating the transmission line. The present invention relates to a method for measuring the level of a stirring tank using a transmission-type level meter for measuring the level of water.

[0002]

2. Description of the Related Art For measuring the level of a stirring tank such as a polymerization tank for producing various resins, a transmission-type level meter capable of measuring the content without contacting the contents, specifically, radiation such as γ-ray is used for the transmission line. Radiation level meters are frequently used. As is well-known, this transmission type level meter has a radiation source section for generating a predetermined transmission line and a detection section for detecting a transmitted dose, with a stirring tank placed inside,
The basic configuration is that the level of the content is measured based on the attenuation that is absorbed and attenuated when a transmission line such as γ-ray passes through the resin or the like of the content.

[0003] More specifically, in a radiation level meter, a radiation source containing radioisotopes and the like, a detector for measuring the intensity of the radiation source such as incident radiation, a radiation of a detection signal from the detector, and the like are included. It comprises a time constant circuit for processing statistical fluctuations and a measuring circuit section comprising a converter for converting the output signal into a predetermined output electric signal.

When a radiation level meter measures the level of a polymerization tank for producing a resin by polymerizing while stirring with a rotating stirring blade, the amount of transmitted radiation reaching the detection unit is determined by the rotation based on the rotation of the stirring blade. It fluctuates intermittently depending on the presence or absence of intersection with the wing. That is, when there is no intersection with the stirring blade, the transmitted radiation dose becomes the attenuation amount due to the absorption of the contents, that is, a signal level corresponding to the level, but when there is an intersection with the stirring blade, the transmitted radiation dose becomes the stirring blade. The signal level becomes lower by that amount due to the extra attenuation due to the absorption of the gas, and the output signal of the level meter fluctuates intermittently according to the rotation of the stirring blade even if the level of the contents is constant. . Conventionally, in order to eliminate such intermittent fluctuation, the setting of the time constant of the time constant circuit is set to a long time limit, and the level signal is smoothed and output.

[0005]

However, this conventional method has the following problems. One of the problems is that the level measurement range is reduced. That is, even if it is desired to increase the range of the level to be measured in order to improve the productivity and increase the capacity of the tank, in other words, to increase the size (specifically, in the case of a vertical polymerization tank, the height of the tank is increased. In the case of a horizontal polymerization tank, the diameter is increased.) Since the transmitted radiation is absorbed by the stirring blade, there is a limit to the transmitted dose to be absorbed by the contents, which is the object of the level measurement, that is, the radiation source capacity. This is a problem that a large capacity cannot be realized. Although there is a means for avoiding this by increasing the source capacity, in the case of radiation, there is an upper limit to the source capacity, and in many cases, this means cannot be taken.

Another problem is that the measurement error increases. That is, both the period of the detection signal of a relatively high level corresponding to the level of the content not absorbed by the stirring blade and the period of the detection signal of a very low level absorbed and greatly attenuated by the stirring blade have both a large time constant. Even if the level of the contents actually fluctuates with the time constant circuit, the fluctuation of the output signal is reduced, and the level measurement accuracy (sensitivity) in the tank is deteriorated overall. is there. The present invention has been made in view of the problems of the prior art in the above-described level measurement of the stirring tank, and is not affected by the stirring blade, and has an inherent level measurement range of the level meter. It is intended to provide.

[0007]

The above-mentioned object is achieved by the present invention described below. That is, according to the present invention, when measuring the level of the stirring tank that stirs the contents with the rotating stirring blade using a transmission-type level meter that measures the attenuation of the transmission line, the stirring blade does not block the transmission line of the level meter. A level measuring method for a stirring tank, wherein a level is measured based on an output signal of a level meter during a non-interruption period.

In the above-mentioned present invention, there is provided a cut-off detecting means for detecting a non-cut-off period or / and a cut-off period in which the stirring blade blocks the transmitted light, and is synchronized with the non-cut-off period detected by the cut-off detecting means. A configuration for extracting the output signal of the level meter is preferable from the viewpoint of stability detection. Among them, a configuration in which the cutoff detection means includes a rotation position detector that detects the rotation position of the stirring blade, and a period determination means that determines a non-cutoff period or / and a cutoff period by comparing the rotation position with a preset position, and It is preferable in terms of reliability and reliability that the rotational position detector be a rotational position detector that detects the rotational position of the drive shaft of the stirring blade. Further, the configuration in which the cut-off detecting means compares the preset set value with the output signal of the level meter to determine the cut-off period or the non-cut-off period is slightly less reliable than the former. However, it is simple and preferable in terms of cost.

On the other hand, the level signal representing the level is continuously output by holding the final value or the average value of the output signal of the level meter in the most recent non-interruption period during the interruption period in which the stirring blade blocks the transmission line of the level meter. Is preferable from the viewpoint of monitoring and control.

As described above, according to the present invention, since the level is measured by the signal during the period when the transmission line is not blocked by the stirring blade, there is no need for averaging with a conventional circuit having a large time constant. Therefore, a level measurement method of a stirring tank that realizes the performance as designed by the level meter without substantial reduction of the measurement range is realized.
Hereinafter, the present invention will be described in detail based on an example in which a gamma ray level meter is used in a polymerization tank as a resin manufacturing apparatus.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 are explanatory views of a vertical polymerization tank and a horizontal polymerization tank of two typical examples of known polymerization tanks as is apparent from the figures, and FIG. It is sectional drawing in the AA 'line. The polymerization tank 6 shown in FIGS. 1 and 2 is provided with a stirring blade 10 which is driven at a predetermined rotation speed via a drive shaft 5 by a rotary drive device 4 (not shown in FIG. 1) composed of an electric motor or the like as shown in the figure. A resin tank is produced by performing a polymerization reaction while stirring the raw materials of the contents.

In this production, as known, there are a batch method and a continuous method. In the case of the batch type, as described in the vertical polymerization tank of FIG. 1, the raw materials are charged to the polymerization tank 6 from respective supply pipes (not shown) to a predetermined level. The reaction is stopped when a predetermined degree of polymerization is reached, and the resin is obtained by discharging the resin obtained from the outlet 9 at the bottom of the polymerization tank 6.

On the other hand, in the continuous type, the raw material is continuously supplied to the polymerization tank 6 from the inlet 8 so that the level in the tank becomes constant, as described in the horizontal polymerization tank of FIG. The polymer is produced by causing a polymerization reaction while stirring with a stirring blade 10 and taking out a resin having a predetermined polymerization degree from the outlet 9 at a constant flow rate.

The stirring device for the horizontal polymerization tank 6 is as follows:
As shown in FIG. 3, a plate-like rotating blade is inclined inside a cylindrical rotating container 7, both ends of which are supported by a driving shaft 5 and provided concentrically with a polymerization tank 6, as shown in FIG. As is clear from the point described later, it is difficult to avoid blocking of the transmission line of the level meter by the stirring blade 10 and the blocking period is long. The effect is remarkable.

As is clear from the above description, in the polymerization tank 6, the level in the tank is an important condition affecting the resin quality, and is controlled by a level meter. As the level meter, a commercially available radiation level meter that is a transmission-type level meter whose measurement is reliable, specifically a γ-ray level meter, is used, as shown in FIGS. 1 are provided so as to be opposed to each other in the axial direction in FIG. 1 and in the radial direction in FIG. 2 with the polymerization tank 6 interposed therebetween so that the level in the polymerization tank 6 can be measured. Are arranged so as to pass through the fluctuation range of the liquid level of the contents. The detection signal 11 from the detection unit 2
Is output.

The detection signal 11 from the detection unit 2 is conventionally converted into a predetermined continuous level signal by a measurement circuit unit shown in FIG. 6 and output, and monitored and controlled by the measurement circuit unit. That is, the detection signal 11 from the detection unit 2 is
After being shaped into a pulse signal having a predetermined pulse waveform by the waveform shaping circuit 12 of the measuring circuit section, it is further converted into an analog signal proportional to the number of pulses per unit time, and then smoothed by the time constant circuit 13 having a predetermined time constant. Is displayed on the converter 14,
The signal is converted into a level signal in a predetermined range adapted to the controller and output. The level measurement result of this conventional level meter in the horizontal polymerization tank shown in FIG. 2 shows the output signal of the waveform shaping circuit 12 that clearly shows the influence of the stirring blade 10, and the stirring blade 10 cut off the transmission line. A periodic signal, which is periodically and greatly reduced to a fraction of the time when it is not cut off, is determined by the number of blades of the stirring blade 10 and the rotation speed. Conventionally, this signal has been processed by increasing the time constant of the time constant circuit 13 and smoothing the signal.

On the other hand, in the present embodiment, there is provided a cut-off detecting means for detecting whether or not the transmission line is cut off by the rotary blade 10 as described below. That is, as shown in FIGS. 1 and 2, a take-out ring 3a is provided on the drive shaft 5 of the stirring blade 10, and the take-out ring 3a and the detection roll 3b of the rotational position detector 3 are connected by a belt 3c to detect the rotational position. Vessel 3
To detect the rotational position of the stirring blade 10, that is, the drive shaft 5 from the reference position, and obtain a rotational position signal.
In this example, a commercially available optical rotary encoder (manufactured by Ono Sokki Co., Ltd., type PR) is used as the rotational position detector 3.
-2112D) was used.

On the other hand, as shown in FIG. 4, also in the measurement circuit section, a gate operation circuit 15 is provided between the waveform shaping circuit 12 and the time constant circuit 13, and the rotation from the rotation position detector 3 for controlling this circuit is provided. A rotation position detection circuit 16 which is a period determination means for determining a cutoff period or a non-blocking period from a position signal is provided, according to a rotation position signal from the rotation position detector 3, that is, whether or not the stirring blade 10 blocks transmission lines. Then, the level signals are synthesized as follows.

That is, the rotation position detection circuit 16 includes a setting unit for presetting a cut-off rotation position at which the stirring blade 10 blocks transmission light from the reference position. In comparison with the rotation position signal, it is determined whether or not the stirring blade is at the shut-off rotation position.When the stirring blade is at the shut-off rotation position, the gate close signal is output, and otherwise, the gate open signal is output. It is composed.

The gate operation circuit 15 receives the gate opening / closing signal, passes the shaped output signal from the waveform shaping circuit 12 as it is to the time constant circuit 13 when the gate is open, and performs the shaping when the gate is closed. It comprises a gate circuit for cutting off the output signal, and an averaging circuit for averaging the shaped output signal when the gate is open and holding and outputting the average value when the gate is closed.

Therefore, during the non-blocking period in which the transmission line is not blocked by the agitating blade 10, a signal for opening the gate is output from the rotation position detecting circuit 16, and the gate circuit of the gate operation circuit 15 is opened to perform shaping from the waveform shaping circuit 12. Since the output signal passes as it is, a level signal obtained by directly converting the detection signal 11 is output. On the other hand, during the cutoff period, the gate closing signal is output from the rotational position detection circuit 16, the gate operation circuit 15 closes the gate circuit to cut off the shaped output signal, and the gate circuit closes the gate circuit from the average value circuit. The average value of the shaped output signal calculated in the open, ie, non-interrupted period is output. Therefore, the output level signal is a continuous signal consisting of the measured value of the actually detected level during the non-blocking period, and a continuous signal consisting of the average value of the measured values of the immediately preceding non-blocking period during the non-blocking period. An adapted signal is obtained.

As described above, in this embodiment, since the level signal is obtained from the measured value during the non-interruption period, the measurement is performed in a state where the transmission line is not absorbed by the stirring blade, as in the tank without the stirring blade. Measurement can be performed according to the level meter performance without reducing the measurement range. Further, since the measured values of the cutoff period and the non-cutoff period are not averaged, it is not necessary to increase the time constant of the time constant circuit, and therefore, the measurement can be performed with the level meter's original accuracy and responsiveness. As described above, according to the present embodiment, the level measurement of the stirring tank without the conventional problem is realized.

By the way, in the above-mentioned example, the structure of detecting the position of the stirrer blade whose operation is stable as the cut-off detecting means and judging the cut-off period and the non-cut-off period is shown, but the structure shown in FIG. Can also be applied. The example of FIG. 5 is an example in which all processing is performed by an electronic circuit. As shown in the figure, a gate operation circuit 1 is provided between a waveform shaping circuit 12 and a time constant circuit 13 of the measurement circuit section.
5 is provided in the same manner as in the example of FIG. 4 described above, and the configuration of this gate operation circuit 15 is also as described above.

In the present embodiment, the cutoff detecting means compares the preset set value with the shaped output signal from the waveform shaping circuit 12, and if the shaped output signal is equal to or greater than the set value, that is, the stirring blade 10 cuts off the transmission line. The comparison circuit 17 outputs a gate open signal during a non-interruption period during which the gate is open, and a gate close signal during an interruption period less than the set value, that is, during the interruption period. Therefore, it operates in the same manner as the example of FIG. 4 and outputs the same level signal. The example of FIG. 5 utilizes a large difference between the signal levels of the above-described cutoff period and non-cutoff period, and is slightly inferior to the example of FIG. 4 in that it is affected by measurement noise and the like. It can be realized by a simple circuit, is advantageous in cost, and can be advantageously applied to a process with less noise.

In the above-described example, the level signal in the cut-off period is held at the average value of the immediately preceding non-cut-off period in order to reduce the influence of noise. Alternatively, the signal may be held at the latest level signal of the immediately preceding non-interruption period. This has the advantage of simplifying the circuit configuration.

Although the present invention has been described based on the embodiments, it is apparent from the gist that the present invention is not limited to the embodiments. For example, in the above-described example, the polymerization tank was described as an example, but similarly, it can be widely applied to a stirring tank having stirring blades in general, and the level meter is also a γ-ray level meter. It is obvious from the gist that the present invention can be widely applied to a transmission-type level meter that performs measurement based on the above. Furthermore, although the measurement circuit section is shown as being constituted by an electronic circuit, it is clear from the gist that these may be processed by a computer. The present invention includes such design changes and common sense modifications.

[0027]

As described above, according to the present invention, the level measurement range, measurement accuracy, and responsiveness, which were limited by the stirring blade, in the level measurement of the stirring tank using the transmission type level meter can be changed according to the original performance of the level meter. The level can be measured even in a large-capacity stirring tank with a relatively small source capacity similar to a tank without a stirring blade. In addition to equipment costs, it is possible to reduce the management area when using radiation and further reduce maintenance costs. As described above, the present invention has an industrially important effect.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a configuration of a vertical polymerization tank according to an embodiment.

FIG. 2 is an explanatory diagram of a configuration in a horizontal polymerization tank of an example.

FIG. 3 is a sectional view taken along line AA ′ of FIG. 2;

FIG. 4 is a block diagram of a measurement circuit unit according to the embodiment.

FIG. 5 is a block diagram of another embodiment of the measuring circuit unit.

FIG. 6 is a block diagram of a conventional measurement circuit unit.

[Description of Signs] 1 Source section 2 Detecting section 3 Rotational position detector 4 Rotary drive device 5 Drive shaft 6 Stirrer tank 7 Rotating container 8 Inlet 9 Outlet 10 Rotating blade 11 Detection signal 12 Waveform shaping circuit 13 Time constant circuit 14 Conversion 15 Gate operation circuit 16 Rotational position detection circuit 17 Comparison circuit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Katsunari Yoshimoto 2-1-1 Uchisaiwaicho, Chiyoda-ku, Tokyo Teijin Engineering Limited F-term (reference) 2F014 FD00 GA01 4G036 AA04 AA23 4G037 DA18 EA04 4G078 AA20 BA01 BA05 CA08 DA03

Claims (10)

[Claims] When measuring the level of a stirring tank for stirring contents with a rotating stirring blade by a transmission type level meter which measures attenuation of a transmission line, the stirring blade does not block the transmission line of the level meter. A level measuring method for a stirring tank, wherein a level is measured based on an output signal of a level meter during a shutoff period. 2. A system according to claim 1, further comprising: a cut-off detecting means for detecting a non-cut-off period or / and a cut-off period in which the stirring blade blocks the transmission line. The method for measuring the level of a stirring tank according to claim 1, wherein the extraction is performed. 3. The shut-off detecting means includes a rotational position detector for detecting a rotational position of the stirring blade, and a period determining means for comparing a pre-set position to determine a non-cut-off period and / or a cut-off period. The method for measuring the level of a stirring tank according to claim 2. 4. The method according to claim 3, wherein the rotation position detector is a rotation position detector for detecting a rotation position of a drive shaft of the stirring blade. 5. The level measuring method for a stirring tank according to claim 2, wherein the cutoff detecting means comprises a comparing means for comparing a set value set in advance with an output signal of the level meter to determine a cutoff period or a non-cutoff period. . 6. A level signal representing a level is a continuous signal in which a final value of an output signal of a level meter in a latest non-interruption period is held during a shut-off period in which the stirring blade blocks a transmission line of the level meter. Item 6. The level measuring method for a stirring tank according to any one of Items 1 to 5. 7. A level signal representing a level is a continuous signal in which an average value of an output signal of a level meter in a non-interruption period immediately before the stirring blade is intercepted by a stirring blade to interrupt a transmission line of the level meter is retained. Item 6. The level measuring method for a stirring tank according to any one of Items 1 to 5. 8. The method according to claim 1, wherein the level meter is a radiation level meter whose transmitted light is radiation. 9. The method according to claim 7, wherein the level meter is a γ-ray level meter whose radiation is γ-ray. 10. The stirring tank is a horizontal polymerization tank.
10. The method for measuring the level of any one of the stirring tanks according to item 9.