KR101802474B1 - An absolute liquid level measuring equipment using two absolute encoders and measurement method it using the same - Google Patents

Abstract

The present invention relates to an apparatus and a method to measure a liquid level using two absolute encoders to precisely measure a level of liquid, such as a water level of a dam, a river, or a port, an oil level of an oil tank, a water level of a large facility of water supply facility, etc. and measure change in a water level even when power supply is blocked. According to the present invention, the apparatus comprises: a float (157) floating on a liquid surface to be measured to be vertically moved in accordance with a change in the liquid surface; a timing pulley (151) receiving a vertical moving distance of the float (157) through a timing belt (158) to convert the same into a rotational amount; an absolute displacement meter (100) receiving the rotational amount of the timing pulley (151) and measuring the same through two absolute encoders coupled through a deceleration gear (106) to output an output value; and a liquid level measurement controller (200) analyzing the output value of the absolute encoders of the absolute displacement meter (100) to calculate an absolute position value of the float (157) and calculating a value of the liquid level in accordance with a calculated absolute position of the float (157). Accordingly, provided is an effect capable of precisely measuring the change in the water level.

Description

TECHNICAL FIELD [0001] The present invention relates to an apparatus and a method for measuring a liquid level using two absolute encoders,

More particularly, the present invention relates to a liquid level measuring apparatus and method, and more particularly, to a liquid level measuring apparatus and a liquid level measuring method using two absolute encoders, And a measurement method using the two absolute type encoders which can measure the level of the water level accurately even when the power supply is cut off.

The liquid level measuring device for measuring the level of a dam, a river or a harbor, a liquid level of a storage tank at a refinery, a crude oil level of a crude oil storage facility stored in a rock wall, and a water level of a water supply facility is very important It is one of the facilities that plays a role.

In general, a float is provided on a liquid surface so as to move up and down according to a liquid level by a liquid level measurement method. A wire rope is connected to the float and then wound on a pulley of a liquid level measuring apparatus. A method of measuring the water level by sensing the movement of the wire rope according to the change through the amount of rotation of the pulley is mainly used.

Conventionally, an R / D converter that measures the amount of rotation of a pulley connected with such a wire rope, a weak magnet is mounted on a 4-digit or 5-digit number wheel, and a reed relay is operated by the magnetic force of the magnet to read the rotation position The device is mainly used. When the 1-digit number is increased to 0, 2, 3, .., 9 and then to 0, the R / D converter increments the 10-unit number wheel by 1 unit and the 10- .., 9, and when it is changed back to 0, the 100 digit wheel is incremented by 1 unit.

In this way, the method of detecting the value of the number wheel is to display the numerical value by using the BCD system composed of four reed relays having the values of 1, 2, 4, 8 per number unit, And outputs a numerical value as a reed relay operated by the reed relay. At this time, the reed relay has a very weak structure in which a contact is attached or dropped due to a weak magnetic force line, so that a phenomenon that the operation is not normally performed due to a weak contact voltage is destroyed due to a weak surge voltage, There is a phenomenon that the value is instantaneously output as 0 when passing through the section without the magnet, and the operation of the facility is stopped.

On the other hand, an incremental encoder is attached to one side of the pulley for measuring the level of the liquid level by another liquid level measurement method, and the pulses generated in accordance with the amount of rotation of the pulley are integrated, and the accumulated pulse value is multiplied by the feed distance coefficient per pulse Measuring methods are also used. However, if there is a change in the level of the liquid level after a power failure or an abnormality in the connection cable of the incremental encoder or a problem in the controller, the level of the liquid level may be changed. There is a problem in that an error of the level value occurs by that much.

On the other hand, there is a method of using an absolute encoder as another liquid level measuring method. In this method, since only one absolute encoder is used, when a long moving distance is measured, a complicated reduction gear is provided at the front end of the encoder, Decelerate the movement within one revolution of the absolute encoder and use it. When the reduction gear is used, a large error occurs due to the backlash of the gear. The accuracy of the absolute encoder obtained by dividing the total travel distance by the resolution of the encoder is relatively long as the travel distance is long. For example, if the variation in the level of the liquid surface is 50 m, and the absolute encoder of 1000 pulse resolution is used, the minimum resolution per pulse is 5000/1000 = 5 cm, which satisfies the minimum resolution of 1 cm And can not be used.

Korean Registered Patent No. 10-0968791 (Registered on July 1, 2010)

SUMMARY OF THE INVENTION The present invention has been proposed in order to solve the problems of the related art as described above, and it is an object of the present invention to prevent a wire from being separated from a pulley due to a sudden change in water level, It provides a function to set the zero point of the liquid surface when the level of the liquid surface must be reset for maintenance. It is possible to precisely measure the liquid level change by using two absolute type encoders, and the liquid level And an absolute value system liquid level measuring device and a measuring method using two absolute type encoders which can measure the liquid level change immediately after power is applied even when the power level is fluctuated.

According to an aspect of the present invention, there is provided an apparatus for measuring a liquid level using an absolute encoder, comprising: a float which floats on a liquid level to be measured and moves up and down according to a change in a liquid level; A timing belt pulley that receives the vertical movement amount of the float through a timing belt and converts the amount of rotation into a rotation amount; An absolute displacement gauge which receives the amount of rotation of the timing belt pulley and measures and outputs the amount of rotation of the timing belt pulley through two absolute type encoders coupled through a reduction gear; And a liquid level measurement controller for analyzing the absolute encoder output value of the absolute displacement gauge to calculate the absolute position value of the float and calculate the liquid level value according to the absolute position of the calculated float.

Here, the absolute displacement meter includes a precision encoder, which is an absolute encoder for precision measurement, coupled to a rotating shaft that receives rotation of the timing belt pulley through coupling, and measures and outputs a value corresponding to a rotation angle of the rotating shaft; A reduction gear formed of a plurality of gears that are engaged with gears formed on the rotary shaft to reduce a rotation speed of the rotary shaft; And a wide-angle encoder which is installed on an axis of a gear installed at a last end of the reduction gear and measures a value corresponding to a decelerated rotation angle and outputs the measured value.

The liquid level measuring controller calculates the number of revolutions of the precise encoder using the value of the wide-angle encoder, multiplies the calculated number of revolutions of the precise encoder by the resolution of the precise encoder, Calculate the position value. Here, the liquid level measuring controller checks the precision encoder rotation number calculation table in which the step-up lower limit value, the step-up upper limit value and the down step-band value are set for each revolution number of the precision encoder, A table index value in a range that is equal to or greater than a step-up lower limit value of the encoder rotation speed calculation table and smaller than a step-up upper limit value is set as the rotation speed of the precision encoder, Is smaller than the lower limit of the down-step, the down-step correction is performed by subtracting 1 from the set number of revolutions of the precise encoder to calculate the number of revolutions of the precise encoder.

The other end of the timing belt connected to the float is connected to the float, and the other end of the timing belt is coupled to the other end of the timing belt to balance the weight with the float. A timing belt pressing bearing is provided which presses the timing belt to prevent it from separating from the pulley. A side surface of the timing belt pulley is provided with a heater for preventing freezing and a temperature adjusting device for preventing the timing belt from freezing on the timing belt pulley during the winter season so that the temperature of the timing belt pulley and the timing belt are kept constant.

The zero point setting bracket is provided at one side of the liquid level detecting device, and the zero level setting bracket is provided at one side of the zero level setting bracket. A value obtained by subtracting the size of the zero point setting bracket from the height difference between the reference floor and the upper surface of the zero point setting horizon, which is a reference of the liquid level, is provided to the liquid level measuring controller And the zero point of the float is set through the zero point setting of the LCD & Key board in a state where the float is in contact with the bottom of the zero point setting bracket.

Herein, the height of the reference floor is referred to as 'H0', the height difference between the reference floor and the upper surface of the zero point setting horizon is referred to as 'H1', the upper surface of the zero point setting horizon and the zero point setting surface 164, The altitude of the zero point setting surface is calculated as 'H3 = H0 + H1-H2', inputted into the memory of the liquid level measurement controller through the LCD & Key board and stored, When the zero point is set through the LCD & Key board in a state where the float is in contact with the zero point setting surface, the float is set to the value of 'H3', and when the float is moved to the position of 'H4' The water level value (Hw) is calculated as 'Hw = H3 - H4'.

A timing belt winding device for winding a timing belt is connected to the other end of the timing belt, the one end of which is connected to the float and contacts the timing belt pulley. The timing belt winding device includes a belt winding pulley for winding a timing belt, And a belt winding gear for connecting between the belt winding pulley and the belt winding spring.

The liquid level measuring controller includes a precise encoder interface unit to which a measurement signal is input from a precise encoder, a wideband encoder interface unit to which a measurement signal is input from the wideband encoder, and a precise encoder measurement signal and a precise encoder measurement signal through the precise encoder interface unit and the wideband encoder interface unit. And a microprocessor that receives and analyzes the wideband encoder measurement signal and calculates an absolute water level value. The microprocessor filters a cut-off frequency in a measured value by applying a windowed-sinc filter using a Blackman window to correct the slope of the water surface and calculate an accurate liquid level value, windowed-sinc filter) is set to the cut-off frequency fc through the transfer function h [i] through the following equation.

[Mathematical Expression]

(Where fc is the cut-off frequency, M is the filter kernel length, i is the sampling variable 0 = i = M, and K is the unity gain constant)

According to another aspect of the present invention, there is provided a method of measuring a level of a liquid using an absolute encoder, the method comprising: moving the float on the liquid level so that the amount of movement of the float, A belt and a timing belt; Measuring a value corresponding to a rotation angle of the rotation shaft in a precision encoder, which is an absolute encoder for precision measurement, coupled to a rotation axis to which a rotation amount of the timing belt pulley is transmitted, and inputting the value to a liquid level measurement controller; Measuring a value corresponding to a rotation angle decelerated by the reduction gear in a wide-angle encoder which is an absolute encoder for wide-range measurement installed in a reduction gear that decelerates the rotation speed of the basic rotation shaft, and inputting the measured value to the liquid level measurement controller; The rotation speed of the precision encoder is calculated by using the value of the wide-angle encoder measured by the liquid level measuring controller, the rotation speed of the precision encoder is multiplied by the resolution of the precision encoder, Calculating a position value, and measuring a liquid level value according to an absolute position of the calculated float.

Here, the liquid level measuring controller checks the precision encoder rotation number calculation table in which the step-up lower limit value, the step-up upper limit value and the down step-band value are set for each revolution number of the precision encoder, A table index value in a range that is equal to or greater than a step-up lower limit value of the encoder rotation speed calculation table and smaller than a step-up upper limit value is set as the rotation speed of the precision encoder, Is smaller than the lower limit of the down-step, the down-step correction is performed by subtracting 1 from the set number of revolutions of the precise encoder to calculate the number of revolutions of the precise encoder.

According to the absorptive liquid level measuring device and measuring method of the present invention, it is possible to prevent the wire from deviating from the pulley due to a sudden change in the water level, to reset the level of the liquid level after newly installing the liquid level measuring device, It is possible to precisely measure the level change of the liquid level through the absolute encoder and the wide absolute encoder connected through the reduction gear. For example, if the distance of 50 m is 0.48 mm It can be measured precisely in units, and it has the highest precision as a length measuring instrument. In particular, even when the water level fluctuates in a state where the power is cut off by using two absolute type encoders, the level change of the liquid level can be calculated by using the output values of the two absolute type encoders as soon as the power is applied.

1 is a schematic plan view of an absolute water level measuring apparatus according to the present invention,
FIG. 2 is a front view of the absolute water level measuring apparatus according to the present invention,
FIG. 3 is a side view of the absolute water level measuring apparatus according to the present invention,
4 is an example of a timing belt winding apparatus according to the present invention,
FIG. 5 is a plan view and partial cross-sectional view of an absolute displacement meter provided in the absolute water level measuring apparatus according to the present invention,
FIG. 6 is a graph showing a relationship between output values of a precision encoder and a wide-angle encoder provided in an absolute displacement meter according to the present invention,
7 shows an example of a general backlash formed between two gears,
FIG. 8 is a conceptual diagram for measuring the number of revolutions of a precise encoder using a wide-range encoder value according to a conventional method,
9 is a conceptual diagram for measuring the number of revolutions of a precision encoder using a wide-range encoder value according to the present invention,
10 to 12 show an example of a simulation result of continuous movement of the precision encoder and the wide-angle encoder according to the present invention in an Excel program,
13 is a conceptual diagram of a precision encoder rotation number calculation table according to the present invention,
14 is a block diagram of a liquid level measuring controller according to the present invention,
15 is a flowchart illustrating a process of measuring an absolute water level value through the absolute water level measuring apparatus according to the present invention,
16 shows an example of the configuration of parameters used in the absolute water level measuring apparatus according to the present invention,
17 to 19 show an example of characteristics of a windowed-sinc filter according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a conceptual view of a plane installation of an absolute value system liquid level measuring apparatus according to an embodiment of the present invention, FIG. 2 is a front view installation conceptual view of an absolute liquid level measuring apparatus, The absolute value method liquid level detecting apparatus according to the present invention detects the absolute liquid level immediately after power is applied even when the liquid level is fluctuated in a state in which the power supply is interrupted And it is a device which can precisely measure the liquid level by the absolute value method even when the liquid level fluctuation is large.

1 to 4, the absolute value system liquid level measuring apparatus according to the present invention includes a float 157 which floats on a water surface to be measured and moves up and down according to a change in a water level, A timing belt 158 for transmitting the up and down movement amount of the float 157 to the timing belt pulley 151 and a timing belt 158 for transmitting the up and down movement amount of the float 157 to the weight A counterweight 161 mounted on the opposite side of the timing belt 158 to balance the timing belt pulley 151 and the float 157, a bearing support 155 for supporting the weight of the timing belt pulley 151 and the float 157, A coupling 154 for transmitting the amount of rotation of the pulley 151 to the absolute displacement gauge 100 and an absolute displacement gauge 100 for measuring and outputting the amount of rotation transmitted through the coupling 154, The output value of the displacement meter 100 is analyzed and the float 1 57) for calculating a liquid level of the liquid level measuring controller (200), a liquid level measuring controller (200) for calculating a liquid level value by calculating an absolute position value of the liquid level measuring controller And a wireless communication unit 160 such as a CDMA modem or an LTE modem for transmitting the state values of the liquid level measurement controller 200 to the outside in a wireless manner. The rotation axis of the timing belt pulley 151, the bearing support 155, the coupling 154, the LCD & KEY board 131, the wireless communication unit 153, the absolute displacement meter 100, the liquid level measurement controller 200, Etc. are provided in the liquid level detection device.

The absolute displacement meter 100 provided in the liquid level detection device 150 measures the amount of rotation transmitted through the coupling 154 and transmits the measurement result to the liquid level measurement controller 200. The liquid level measurement controller 200 The absolute position of the float 157 is calculated by analyzing the amount of rotation measured through the displacement meter 100, and the absolute value of the liquid level is calculated through the absolute position.

In the embodiment of the present invention, the absolute displacement meter 100 measures the amount of rotation of the timing belt pulley 151 as the float 157 moves up and down through an absolute encoder, The amount of rotation of the timing belt pulley 157 is measured and supplied to the liquid level measuring controller 200 as soon as the power is supplied. On the other hand, since the absolute type encoder can measure only the movement amount with respect to the distance within one revolution, in the present invention, by using two absolute type encoders connected with the reduction gear, the measurement limit within one rotation can be overcome, So as to precisely measure the amount of movement with respect to the moving object.

On the other hand, when the river level is measured using the liquid level measuring device, when the float 157 rapidly rises due to a sudden increase in water level or a large peak, the timing belt 158 is separated from the timing belt pulley 151 or slip occurs Resulting in a large error. In order to compensate for this, in the present invention, belt pressing bearings 152 are provided on both sides of the timing belt pulley 151 to closely contact the timing belt 158 so as not to be separated from the timing belt pulley 151. In the present invention, the freezing prevention heater 153 and the temperature regulating device 156 may be provided to prevent the timing belt 158 from being frozen in the timing pulley 151 during the winter season. The timing belt 158 and the timing pulley 151 are maintained at a constant temperature so as not to be frozen by installing the timing belt 158 and the timing pulley 151 in the liquid level detecting device 150 around the timing belt pulley 151. [

A humidity sensor 167 and a space heater 168 are provided on one side of the liquid level measuring controller 200 to prevent condensation from occurring in the internal components of the liquid level measuring controller 200 due to a large amount of moisture in the summer, If the humidity measured by the humidity sensor 167 is higher than the set value or the measured temperature falls below the set value, the space heater 168 is operated to lower the humidity or increase the temperature.

On the other hand, the position of the float 157 should be set to a certain set value when the liquid level measuring apparatus is newly installed or when the liquid level is to be checked during use. That is, a zero point setting surface 164, which is a zero point that is a measurement reference when measuring the level through the float 157, should be set. In the embodiment of the present invention, the zero point setting surface 164 is a zero point And the bottom surface of the zero point setting bracket 163, which is coupled to the setting adjusting device 162 and whose height is adjusted through a height adjusting nut.

3, the elevation of the zero setting surface 164 is calculated through an altitude deviation with respect to the reference floor 183 such that the altitude of the reference floor 183 corresponds to the height of the industrial GPS on the reference floor 183 ), It can be determined by averaging the altitude value transmitted from the satellite or by referring to the altitude value indicated in the structure diagram of the facility. In order to measure the altitude deviation between the reference bottom surface 183 and the zero point setting surface 164, a zero point setting horizon 166 is installed on one side of the altitude reference setting bracket 163. On the other hand, the distance between the reference bottom surface 183 and the upper end of the zero point setting bracket 163 is measured using a digital tape measure or another measuring device to measure the altitude deviation, and this value is measured using the LCD & And inputs it to the measurement controller 200.

For example, the altitude of the reference bottom surface 183 may be referred to as 'H0', the height difference between the reference bottom surface 183 and the upper surface of the zero point setting horizon 166 may be referred to as 'H1' The altitude value H3 of the altitude zero setting surface 164 becomes 'H3 = H0 + H1 - H2', where 'H2' is the height difference between the upper surface of the elevation surface 166 and the zero setting surface 164. At this time, when the height difference 'H1' between the reference bottom surface 183 and the upper surface of the zero setting horizon 166 is not an integer value, the zero setting controller 162 sets the screw of the zero setting controller 162 And adjusts the height of the upper surface of the zero point setting horizon 166 to set it to an arbitrary integer value.

The altitude value H3 of the altitude zero setting surface 164 is inputted through the LCD & Key board 131 and stored in the memory of the level meter controller 200. The float 157 is lifted to set the altitude zero setting surface 164, when the zero point is set through the LCD & Key board 131, the position of the float 157 is reset to the value of 'H3'.

If the float 157 moves to the position of 'H4' by the change of the water level, the water level value Hw is represented as 'Hw = H3-H4'.

On the other hand, when the counterweight 161 is shaken due to the influence of wind on the liquid level measuring device, the counterweight 161 is jammed on the timing belt 158 connected to the float 154 and becomes inoperable or the diameter of the pipe It may occur when the counterweight 161 is difficult to install. In order to prevent this, a timing belt winding device for winding the timing belt 158 instead of the counterweight 161 as shown in Fig. 4 can be applied . This timing belt winding apparatus includes a belt winding pulley 187 for winding a timing belt 158, a belt winding spring 184 for generating power for winding the belt on the belt winding pulley 187 by using the restoring force of the circular spring, A belt winding gear A 185 and a belt winding gear B 185 that connect between the belt winding pulley 187 and the belt winding spring 184.

Hereinafter, an absolute displacement meter 100 that receives the amount of rotation of the timing belt pulley 151 through the coupling 154 and measures the amount of rotation of the timing belt pulley 151 will be described.

5 is a plan view and partial sectional view of an absolute displacement meter according to an embodiment of the present invention.

5, the absolute displacement meter 100 according to the present invention includes a rotation shaft 104 that receives a rotation amount of a timing belt pulley 151 through a coupling 154 and rotates, A precision encoder 112 which is an absolute encoder for precision measurement which is coupled to the rotary shaft 104 and outputs a unique value according to the rotation angle of the rotary shaft 104; And a wide-angle encoder 113, which is an absolute encoder for wide-area measurement, which outputs a unique code value according to the rotation angle reduced by the reduction gear 106 .

The rotation shaft 104 is rotated by receiving the amount of rotation of the timing belt pulley 151 through the coupling 154. The bearing 103 is inserted into the rotation shaft 104 so that the rotation can be smoothly performed .

The precision encoder 112 coupled to the rotation shaft 104 is an absolute type encoder that outputs a unique code value for an arbitrary rotation angle within one rotation of the rotation shaft 104. The precision encoder 112, And outputs an eigenvalue corresponding to the rotation of the rotary shaft 104 according to the resolution, thereby accurately measuring the amount of movement of the rotary shaft 104 within one rotation.

A gear 105 is formed on the rotary shaft 104 and a reduction gear 106 for reducing the rotation speed of the rotary shaft 104 is coupled to the gear 105. In the embodiment of the present invention, And a plurality of gears that are sequentially coupled to the rotary shaft 104 and sequentially decelerate the rotary speed of the rotary shaft 104. That is, in the embodiment of the present invention, the reduction gear 106 includes a first gear 107a, a second gear 107b, and a third gear 107c having appropriate deceleration ratios, The number of reduction gears 106 and the gear ratio can be appropriately changed according to the movement range of the detection subject and a speed reducer or a harmonic driver or the like constituted by a single component can be used by another deceleration method It is possible.

A wide-angle encoder 113 is coupled to the shaft of the third gear 107c located at the last end of the reduction gear 106 that decelerates the rotation speed of the rotary shaft 104. The wide- Is an absolute type encoder that outputs a unique code value for an arbitrary rotation angle within one revolution of the third gear 170c whose rotation speed of the rotation shaft 104 is reduced by the reduction gear 106. [ That is, the third gear 107c makes one rotation when the rotation shaft 104 rotates several times according to the deceleration ratio with respect to the rotation shaft 104. The wide-angle encoder 113 rotates the third gear 107c , The eccentricity can be measured over a wide range corresponding to the number of rotations of the rotary shaft 104.

The values output through the precise encoder 112 and the wide-angle encoder 113 are transmitted to the liquid level measuring controller 200. The liquid level measuring controller 200 includes a rotary shaft 104 provided with the precise encoder 112, The level of the liquid level, which is an absolute level value according to the up-and-down movement of the float, is analyzed by analyzing the output values of the precision encoder 112 and the wide-angle encoder 113 in consideration of the deceleration rate and the backlash error of the third gear 107c .

In the absolute displacement gyroscope 100 having the above configuration, the rotation shaft 104 is rotated in accordance with the rotation of the timing belt pulley 151 connected to the coupling 154, and the rotation shaft 104 ) Outputs an eigenvalue corresponding to the rotation angle within one rotation. The reduction gear 106 composed of the first gear 107a, the second gear 107b and the third gear 107c coupled to the rotation shaft 104 is rotated and rotated according to the rotation of the rotation shaft 104 And the wide-angle encoder 113 coupled to the last end of the reduction gear 106, that is, the third gear 107c axis, outputs an eigenvalue corresponding to the rotation angle within one rotation. The output values of the precision encoder 112 and the wide-angle encoder 113 are analyzed by the liquid level measuring controller 200 to calculate an absolute position value in accordance with the up-down movement of the float 157 for rotating the timing belt pulley 151 , And the liquid level value is calculated through this.

Hereinafter, the process of calculating the liquid level value by analyzing the measured values of the precise encoder 112 and the wide-angle encoder 113 by the liquid level measuring controller 200 will be described.

Since the absolute water level indicating the liquid level is determined according to the positional change of the float 157, it can be obtained by calculating the positional change of the float 157 moving in accordance with the water level change at the reference position. That is, the absolute position is calculated by calculating the distance traveled by the float 157 with reference to the reference floor, and the absolute position of the float 157 is calculated using the wide encoder 113 112 and multiplying the calculated number of rotations of the precise encoder 112 by the resolution of the precise encoder 112 and adding the value of the precise encoder 112 thereto.

The easiest way to calculate the number of revolutions of the precision encoder 112 is to calculate the number of revolutions of the precision encoder 112 at a moment when the value of the precision encoder 112 is changed from 1023 to 0 The number of revolutions of the precision encoder 112 may be reduced by one at the instant when the number of revolutions of the precision encoder 112 is increased by 1 and the number of revolutions of the precision encoder 112 is changed from 0 to 1023. However, this method can not be applied because the number of rotations of the precision encoder 112 can not be calculated by reading the value of the wide-angle encoder 113 at the moment when the power is turned on. In this method, the number of revolutions before the power is turned off is stored in the backup memory, and when the power is supplied, the value is read to know the number of revolutions until the power is turned off. However, Since one quantity can not be calculated, it can not be applied to the absolute position measurement of the float as a result.

FIG. 6 is a graph showing output values of a precision encoder and a wide-angle encoder according to an embodiment of the present invention.

6, when the resolution of the precision encoder 112 and the wide-angle encoder 113 is 1024, the value of the precision encoder 112 increases from 0 to 1023 during one rotation of the precision encoder 112 The wide-angle encoder 113 is moved to the deceleration gear 106 as it is decelerated.

When the value of the precision encoder 112 is Enc_A, the value of the wide-angle encoder 113 is Enc_B, and the resolution of the precision encoder 112 and the wide-angle encoder 113 is 1024, the absolute position value Can be expressed by the following equation (1).

Here, f (Enc_B) is a series of functions for calculating the number of rotations of the precision encoder 112 with the value Enc_B of the wide-angle encoder 113 as a variable. The value of f (Enc_B) .

The first gear 107a, the second gear 107b, the third gear 107c, and the third gear 107c in the process of calculating the number of revolutions of the precision encoder 112 using the value of the wide- There is a non-response region in which the value of the wide-angle encoder 113 does not change even if the rotation axis 104 rotates when the rotation direction of the rotation axis 104 is changed.

In most cases, the value of the wide-angle encoder 113 for one rotation of the precision encoder 112 is not an integer. For example, the first gear 107a, the second gear 107b, the third gear The value A1 of the wide-angle encoder 113 for one rotation of the precision encoder 112 is calculated by the following equation (2): " (1) " .

Since the value of the wide-angle encoder 113 for one rotation of the precision encoder 112 is not an integer as in Equation (2) above, the value of the wide-angle encoder 113 is used because of the backlash existing between the gears, A complicated process is required to calculate the number of revolutions of the rotor 112.

First, backlash existing between gears will be described.

Fig. 7 shows an example of a general backlash formed between two gears. Assume that the amount of backlash between two gears is d ?.

Generally, backlash occurs at the time when the rotational direction of the rotating shaft 104 is changed. In the absolute position measuring apparatus 100 of the present invention, the amount of backlash and the gear ratio between the rotating shaft 104 and the first gear 107a are expressed by d? The backlash amount and the gear ratio of the first gear 107a and the second gear 107b are denoted by d? 2 and Gr2 and the amount of backlash and the gear bar between the second gear 107c and the third gear 107c are denoted by d? The total backlash amount ?? formed between the rotating shaft 104 and the third gear 107c can be expressed by the following equation (3).

The total backlash amount [Delta] [theta] is converted into the value A2 of the precision encoder 112, and can be expressed by the following equation (4).

FIG. 8 is a conceptual diagram for measuring the number of revolutions of a precise encoder using a wide-area encoder value according to a conventional method, FIG. 9 is a conceptual diagram for measuring the number of revolutions of a precise encoder using a wide- .

In general, the absolute position value of the float 157 is obtained by dividing the value of the wide-angle encoder 113 by a predetermined coefficient to calculate the number of revolutions of the precise encoder 112, multiplying the value by the resolution 1024 of the precise encoder 112, And adds the value of the encoder 112 to calculate an absolute position value. However, since the value of the wide-angle encoder 113 is outputted as an integer rather than a real number, a round-off error occurs in the calculation process, and the value of the precision encoder 112 is changed from 0 to 1023 or 1023 A large error of 1024 which is a positive (+) position error or -1024 which is a (-) position error occurs in the portion where 0 is changed.

In order to explain this more specifically, an Excel program is created, and the value of the precision encoder 112 is incremented by 1, four rotations, and then decremented by 1 in the opposite direction, A simulation for calculating the value of the encoder 113 was performed. Also, assuming that the backlash amount [Delta] [theta] is 15, the process of changing the value of the wide-angle encoder 113 due to the delay of signal transmission every time the direction of the precision encoder 112 increases or decreases Respectively. The simulation results for this continuous movement of the precision encoder 112 and the wide-angle encoder 113 are shown in the Excel program of Figs. 10-12.

The simulation items shown in FIG. 10 are classified into a common item, a general calculation, an invention calculation, and a precision encoder rotation number calculation table. The items are as follows.

[Common Items]

In the common item, the B column is incremented by 1 or decremented by 1 to indicate a reference absolute position, the C column represents a process in which the value of the precision encoder 112 is incremented by 1 or decremented by 1, The backlash is expressed on the assumption that the backlash is shifted downward in an apparatus having a backlash amount (??) of 15. The row F represents the theoretical value of the wide-angle encoder 113 taking into account the influence of backlash, The value is expressed as a digital value like an actual encoder output by integrating.

[General calculation]

Column I of the general calculation item indicates the number of rotations of the precision encoder 112 calculated on the assumption that the value of the wide-angle encoder 113 is 972 and the gear ratio to the rotation axis 104 is 90: 1 in the entire stroke, and J Column represents the value of I column which is the number of revolutions of the precise encoder 112 multiplied by the resolution 1024 of the precise encoder 112 plus the value of the precise encoder 112 of the C column and the K column represents the value of the J column Absolute position_general) is subtracted.

[Invention calculation]

In the inventive calculation item, column M refers to the value of the theoretical wide-angle encoder 113, which is the value of the column G, to the number of revolutions of the precision encoder 112 according to Equation 17 described later with reference to the precision encoder rotation number calculation table 420 on the right side And N represents a downstep band value with respect to the number of revolutions of the precision encoder 112 displayed in the column M, and the column O determines whether down-step correction is to be performed according to the following equation (19) When the correction is performed, the value is indicated as 1. When the down-step correction is not performed, the value is indicated as 0. The P column indicates a value obtained by multiplying the number of revolutions of the precise encoder 112 displayed in the column M by the resolution 1024 of the precise encoder 112 plus the value of the precise encoder 112 in the column C, (Absolute position_invention) value in the column.

In the general calculation shown in FIG. 10, the value of the theoretical wide-angle encoder 113 is calculated and integerized for the entire process of incrementing the value of the precision encoder 112 displayed in column C by 1 or decrementing by 1, , The value of the G column is simply divided by the value of the wide-angle encoder 113 for one rotation of the precise encoder 112 to indicate the number of rotations of the precise encoder 112 in the I column, The resolution is multiplied by 1024, and the value of the precision encoder 112 is added to calculate the J-th column.

Further, the invention calculation is performed by calculating the number of revolutions of the M-column precision encoder 112 using the G column value, which is the theoretical wide-range encoder 113 value of the common item, by referring to the precision encoder rotation number calculation table 420, Which is obtained by multiplying the number of rotations of the precision encoder 112 by the resolution 1024 of the precision encoder 112 and adding the value of the precision encoder 112 of the C column. The U column indicates that the value of the precise encoder 112 is 0? 1023 or 1023 (?), And the U column indicates the step-up upper limit value. Step down compensation for eliminating the phenomenon that a large error is generated in the absolute position calculation at the portion where the change is made from 0 to? 0. In the down-step correction, in order to eliminate the occurrence of (+) position error or (-) position error in calculating the absolute position value at the portion where the value of the precision encoder described in FIG. 4 is changed from 0 → 1023 or 1023 → 0 , Subtracting 1 from the number of revolutions of the precise encoder 112 when the value of the wide encoder 113 is smaller than the value of the down step band and the value of the precise encoder 112 is larger than the down step lower limit value . In the practice of the present invention, the lower step lower limit value is set to a constant in the range of 0 to 0.75 of the resolution of the precision encoder 112. Hereinafter, the lower step lower limit value is set to 0.5, that is, 512 of the resolution of the precision encoder 112 A set example will be described.

Fig. 13 is a conceptual diagram of such a precision encoder rotation number calculation table.

A step-up lower limit value 306, a step-up upper limit value 308 and a down step band value 307 of the precision encoder rotation speed calculation table 420 are calculated as follows.

First, the value of the wide-angle encoder 113 is B1, and the number of revolutions of the precise encoder 112 is B2. At this time, if the value of the wide-angle encoder 113 per revolution of the precise encoder 112 is A3 , The above-described equation (2) can be modified as the following equation (5). In this case, the int function is used to convert the value (A3) of the wide-angle encoder 113 per rotation of the precision encoder 112 into an integer value in Equation (5), and 0.5 is added for rounding.

The step-up lower limit value 306 for the number of revolutions N of the precise encoder 112 in the entire stroke and the step-up upper limit value 306 for the number of revolutions N of the precise encoder 112 in the entire stroke can be obtained by using the value A3 of the wide-angle encoder 113 per revolution of the precise encoder 112 (308) and the down step band value (307) are calculated through the following equations.

Here, A3 is the value of the wide-angle encoder per one rotation of the precision encoder of Equation (5), N is the number of rotations of the precision encoder, and int () represents a function of converting real numbers to integers. Α is a constant in the range of 0 to 0.499, β is a constant in the range of 0.5 to 0.999, and γ is a constant in the range of 0 to 0.499.

10 and Fig. 13 based on the step-up lower-limit value 306, the step-up upper-limit value 308 and the down-step band value 307 calculated through the above Expressions (6) The precision encoder rotation number calculation table 420 shown in Figs. 10 and 13 shows an example where? Is set to 0.25,? Is set to 0.75, and? Is set to 0.25. The step-up lower limit value 306 thus set is displayed in the column T, the step-up upper limit value 308 is displayed in the column V, and the downstep band value 307 is displayed in the column U.

In the Excel program of FIG. 10 showing the simulation results of the continuous movement of the precise encoder 112 and the wide-area encoder 113, each row number is sequentially increased. The following equations are obtained for each row of the Excel program The simulation results for each item displayed on the line are shown.

11 shows a process in which the value C1982 of the precise encoder 112 in the column C is 955 and the value G1982 of the wide band encoder 113 in the column G is 21 and the value of the precise encoder 112 is changed to 956 in FIG.

[Example 1 (common), row = 1982]

11, the number of rotations I1982 of the precision encoder 112 in the I column is 1 and the value C1982 of the precision encoder 112 in the C column is 955, the absolute position value J1982 is calculated by the following equation.

Herein, the absolute position value when the precision encoder value increases by one is divided into a general calculation method and a calculation method according to the present invention.

[Example 1A (general calculation method), row = 1983]

As a general calculation method, when the value C1983 of the precision encoder 112 in the column C is increased to 956, the number of rotations G1983 of the wide band encoder 113 in the column G is changed to 22 and the revolution number I1983 of the precision encoder 112 in the general calculation item is Is calculated by dividing the rotation number G1982 of the wide-angle encoder 113 in the G column by the value of the wide-angle encoder 113 per rotation of the precision encoder 112 as shown in the following equation.

The absolute position value J1983 at this time is calculated by the following equation.

Thus, according to the general calculation method, the value of absolute position_general J1983 becomes 3004, which causes a large error of 1024, which is the (+) position error, between the value of absolute position_general J1982 and the value of K1983.

[Example 1B (invention calculation method), line = 1983]

According to the calculation of the present invention, since the number of rotations G1983 of the wide-angle encoder 113 is 22, if the range to which this value belongs is found in the precision encoder rotation number calculation table 420, the lower limit value is 19 and the upper limit value is 30 , The down step band value corresponds to U5 24, and the number of rotations of the precision encoder 112 corresponds to 2 at S5.

In this state, the value G1983 of the wide-angle encoder 113 is 22, and the number of rotations M1983 of the precision encoder 112 is 2. At this time, since the downstep band value U5 is 24, the value of G1983 22 is less than the value 24 of U5, the precision encoder value C1983 is 956, and the lower step lower limit value is larger than 512, the down step correction judgment O1983 becomes 1, and the down step correction should be applied.

Therefore, the absolute position value at this time is calculated by the following equation.

Thus, it can be seen that the value of P1983 increases linearly with respect to P1982.

12 shows the result of calculating the absolute position value for the C column of the precision encoder 112 in a state where the value of the precision encoder 112 is decremented by one.

[Example 2 (common), row = 6447]

12, in the process of changing the value of the precision encoder 112 from 0 of C6447 to 1023 of C6448, the value C6447 of the precision encoder 112 in the C column is 0 and the number of rotations I6447 of the I column precision encoder 112 is 2 , The absolute position value J6447 is calculated by the following equation.

Here, the absolute position value when the row is decremented by one is divided into a calculation method and a calculation method according to the present invention by a general method.

[Example 2A (general calculation method), row = 6448]

The general calculation method is as follows. When the value of the precision encoder 112 in the C column is changed from C6448 to 1023, the number of revolutions G6448 of the wide-angle encoder 113 in the G column is not changed to 22 and the number of revolutions I6448 in the I column precision encoder 112 is 2, the absolute position value J6448 is calculated by the following equation.

Thus, according to the general calculation method, the value of absolute position_general J6448 becomes 3071, which causes a large error of 1024 as in the case of absolute position_general J6447 and K6448.

[Example 2B (Inventive calculation method), row = 6448]

According to the calculation of the present invention, since the number of revolutions G 6448 of the wide-angle encoder 113 is 22, if the range to which this value belongs is found in the precision encoder revolution number calculation table 420, the lower limit value is 19 and the upper limit value of T 5 is 30 , The down step band value corresponds to U5 24, and the number of rotations of the precision encoder 112 corresponds to 2 in S5.

The value G6448 of the wide-angle encoder 113 is 22, and the number of rotations of the precision encoder 112 is M6448 is 2, and since the downstep band value U5 is 24, the value of G6448 22 is less than the value 24 of U5 and the precision encoder value C6448 is 1023, which is greater than the downstep lower limit value of 512, and the downstep correction judgment O6448 becomes 1, and the downstep correction should be applied.

Therefore, the absolute position value at this time is calculated by the following equation.

Thus, it can be seen that the value of P6448 is 1 linearly decreased compared to P6447.

10 to 13, in the present invention, the rotation speed of the precision encoder 112 is calculated by applying the step-up lower limit value, the step-up upper limit value and the down-step band value according to the value of the wide- (+) Position error or (-) position error at the portion where the rotation number of the precision encoder 112 is changed from 0 → 1023 or 1023 → 0 can be completely eliminated by calculating the absolute position value based on this, The absolute position value can be calculated.

Hereinafter, the configuration and operation of the liquid level measuring controller 200 for calculating the absolute water level through the absolute position of the float 157 will be described.

14 is a block diagram of a liquid level measuring controller according to an embodiment of the present invention.

14, the liquid level measuring controller 200 according to the present invention includes a precision encoder interface unit 204 to which a measurement signal is input from the precision encoder 112, And a microprocessor 201 for analyzing measurement signals of the precision encoder 112 and the wide-angle encoder 113 and calculating an absolute water level value. The liquid level measuring controller 200 is provided with a DC / DC converter 208 for supplying power, an FRAM memory 203 for storing various parameters and variables, and an RS-232C communication unit 209 And a limit signal output unit 211 for outputting a limit signal for limiting the operation range of the apparatus to an external control device. An optical communication unit 212 for transmitting and receiving optical signals, an Ethernet communication unit 214 for transmitting data in an Ethernet system, and a wireless transceiver unit 215 for transmitting and receiving data in a wireless manner.

The precision encoder interface unit 204 is connected to the precision encoder interface unit 204. The precision encoder interface unit 204 adjusts the level of a signal input from the precision encoder 112, And converts the signal into a binary number and inputs the binary number to the microprocessor 201. Preferably, the time constant of the RC filter is designed to be higher than the maximum frequency of the precision encoder 112.

The wide-angle encoder interface unit 206 is connected to the wide-angle encoder interface unit 206. The wide-angle encoder interface unit 206 adjusts the level of a signal input from the wide-angle encoder 113, And converts the signal into a binary number and inputs the binary number to the microprocessor 201. It is preferable that the time constant of the RC filter is designed to be higher than the maximum frequency of the wide-angle encoder 113.

The DC / DC converter 208 converts the external DC 24V power supply 123 to DC 5V and supplies it to the operation power supply of the liquid level measurement controller 200.

The microprocessor 201 analyzes signals input through the precision encoder interface unit 204 and the wide-angle encoder interface unit 206 to calculate the absolute position and level of the float 157. The microprocessor 201 201 are provided with a flash memory in which a program for analyzing measurement signals of the precision encoder 112 and the wide-angle encoder 113 and calculating an absolute water level value, and an SRAM for storing various variables. A USB port 202 is connected to the microprocessor 201. A notebook computer 130 is connected to the USB port 202 so that the notebook computer 130 and the microprocessor 201 can communicate with each other through a USB communication method. The notebook computer 130 transmits an operation program to the microprocessor 201 or transmits parameter values to be set.

The FRAM memory 203 is a nonvolatile memory whose contents are not erased even when the power is turned off. The FRAM memory 203 stores a parameter value transmitted from the notebook computer 130 or an external device or stores important parameter values .

The RS-232C communication unit 209 is a circuit for communicating with an external device such as an external keyboard or an LCD & Key board 131, and inputs or modifies parameters through a keyboard connected to the RS-232C communication unit 209 And the operation state is displayed on the LCD & Key board 131. The keyboard and the keyboard can also be operated to display the pressed state of the keyboard or the state of the device and the alarm state through the buzzer.

The RS-485 communication unit 210 is a communication circuit that performs a function of transmitting an absolute value or an operation state value to the CDMA modem 153 or the LTE modem according to a half-duplex communication system. The RS- MODBUS-RTU or MODBUS-ASCII or CAN communication or CC-Link method, the signal is transmitted through the protocol such as PLC protocol specified in the parameter. The RS-485 communication unit 210 also performs a function of exchanging signals by radio such as a CDMA modem, an LTE modem, WIFI, ZIGBEE, and transmitting / receiving data by installing a media converter on the outside.

The liquid level value output unit 211 is a circuit for outputting the absolute water level value calculated by the microprocessor 201 to the upper monitoring device A 132. The level value output unit 211 uses the optical insulating device And converts the voltage into a voltage for driving a relay or an open collector device and outputs the voltage as a relay contact signal or an open collector output signal. As shown in FIG. 16, if the value is 1, the signal output through the liquid level value output unit 211 is a BCD signal if the value is 1, a binary signal if the value is 2, and 3 if the value is 3 according to the value set in the Para_Output parameter And output in gray code form.

The limit signal output unit 212 outputs Para_Pos1, which outputs a signal to the upper control device B 133 when the absolute position value reaches or exceeds the set position value 1, If it exceeds, there is Para_Pos2 which outputs a signal.

The optical signal transmitting and receiving unit 213 is a circuit for receiving or outputting signals of a glass optic fiber or a plastic optic fiber. The optical signal transmitting and receiving unit 213 transmits and receives data to and from the outside through an external optical signal converter 134 and an optical fiber, And functions to protect the device by blocking the incoming surge signal.

The Ethernet communication unit 214 transmits data to the upper monitoring apparatus C 135 using a protocol such as MODBUS-TCP using Ethernet as a medium, EtherCAT, EthernetIP, Profinet, and CC Link IE.

The wireless transceiver unit 215 wirelessly transmits the measured level to the main monitoring unit, since the liquid level measuring apparatus is often installed at a separate external location. The wireless transmitting / receiving unit 215 includes ZIGBEE, And transmits and receives data to and from an external device through an antenna 136 provided outside the WIFI or a 424 MHz wireless system, which is a frequency for data transmission.

When the float 157 reaches the position of the zero point setting surface 164, the liquid level controller 200 having the above-described structure, through the zero point input of the LCD & Key board 131, The value of the precise encoder 112 and the value of the wide area encoder 113 inputted through the encoder interface unit 204 and the wide area encoder interface unit 206 are immediately transferred to the precision encoder zero value area And the wide encoder zero point value area.

In the embodiment of the present invention, since the precision encoder zero value and the wide encoder zero value are important values based on the measurement, three consecutive values are stored, and in the process of reading the parameter after power supply, Even if the values of the two values are different, if the two values match, it is recognized as a correct value, thereby improving the reliability.

When the zero point value is set through the above process, the microprocessor 201 calculates a result value obtained by subtracting the zero value of the wide-angle encoder 113 from the value of the raw wide-angle encoder 113 input through the wide-angle encoder interface unit 206 every predetermined scan And the value of the precision encoder 112 is also calculated from the value of the raw precision encoder 112 input through the precision encoder interface unit 204 minus the precision encoder 112 zero value . That is, the value of the wide-angle encoder 113 and the value of the precise encoder 112 are calculated by the following equation.

15 is a flowchart illustrating a process of measuring an absolute position value through an absolute water level measuring apparatus according to an embodiment of the present invention.

Step S100: When the measurement is started through the periodic interrupt (1 ms), the amount of movement of the float 157 which floats on the water surface and moves up and down according to the change of the water level is transmitted through the timing belt 158 and the timing belt pulley 151 And is then transmitted to the absolute displacement meter 100. [ Accordingly, the absolute encoder 112 and the wide-angle encoder 113 provided in the absolute displacement meter 100 transmit the output value corresponding to the rotation to the liquid level measurement controller 200. The wide area encoder value A is first calculated by the liquid level measuring controller 200 in such a manner that the wide area encoder value A is input to the wide area encoder 203 through the wide area encoder interface 203, A0) of the wide-angle encoder 113 is subtracted.

Step S110: When the wide-angle encoder value A is calculated, the precise encoder value B is also calculated as the precise encoder value B input through the precise encoder interface unit 202, Is a value obtained by subtracting the zero point value of the precision encoder 112 set in the binary encoder B0.

Steps S120 and S130: In order to calculate the absolute position value through the wide-angle encoder value A and the precise encoder value B calculated through the above process, the precision encoder 112 The step up index value, which is a value for finding the number of rotations, is set to 0 (S120), and the step up upper limit value, the step up lower limit value and the down step_band value for the step up index value are read (S130).

Steps S140, S141, and S142: Next, in order to determine whether to perform down-step correction, it is first determined whether the wide-angle encoder value A is equal to or greater than the step-up lower limit value (S140). If the wide-angle encoder value A is smaller than the step-up_lower limit value, the step-up index is incremented by one (S141). If the incremented step-up index value is greater than or equal to the maximum index value, If it is greater than or equal to S130, the fine position calculation process is terminated (S142).

Step S150: If the wide-angle encoder value A is greater than or equal to the step-up-lower limit value, it is determined whether the wide-angle encoder value A is smaller than the step-up_limit value. If the wide- If it is not smaller than the upper limit value, the process goes to step S413 and the step up index value is incremented by one.

Step S160: If the wide-angle encoder value A is equal to or greater than the step-up lower limit value and smaller than the step-up upper limit value, the step-up index value is input as the number of rotations of the precision encoder 112.

Step S170, S180, and S190: It is determined whether the wide encoder value A is smaller than the downstep band value to determine whether the down-step correction is to be applied (S170). If the precision encoder value B is smaller than the down- (S180). If it is greater than 512, down-step correction is performed to subtract 1 from the number of rotations of the precision encoder 112 (S190). On the other hand, if the wide-range encoder value A is not smaller than the down-step band value or the fine encoder value B is not larger than the down-step lower limit value 512, down-step correction is not applied. The lower step lower limit value 512 is a value set to 0.5 of the precision encoder resolution when the resolution of the precision encoder 112 is 1024, which can be appropriately changed within the range of 0 to 0.75 of the precision encoder resolution.

Step S200: When the number of revolutions of the precise encoder 112 is calculated through the above process, the number of revolutions of the precise encoder 112 is multiplied by the resolution of the precise encoder 112 and the value of the precoder 112 And the absolute position value is calculated.

Step S210: The absolute position value calculated through the above process is the absolute position value of the float 157, which means the position movement value of the float 157 according to the water level change, i.e., the movement value of the timing belt 158 . Accordingly, the liquid level measuring controller 200 calculates the absolute level value, i.e., the liquid level value, by calculating the height deviation of the reference bottom surface + the height deviation of the reference setting surface-the float of the timing belt, .

The microprocessor 201 is connected to the LCD & Key board 131 or the USB port 202 or the RS port 202. The RS < RTI ID = 0.0 > -485 communication unit 210, stores the parameter in the FRAM memory 205, and initializes each corresponding variable of the microprocessor 201 in a reset operation at the instant when power is supplied to perform various calculations and functions To be implemented.

When the liquid level is low, the weight of the timing belt is shifted toward the float 158 so as to cancel the weight of the counterweight 161. When the liquid level is at the high level The weight of the timing belt is biased toward the counterweight 161 and added to the weight of the counterweight 161 so that the weight of the timing belt according to the level of the liquid surface lifts or floats the float 158. [ Para_Optset for setting the output type to BCD or binary, Para_Baud for setting the communication speed, and the actual physical quantity 1000 mm, and Para_Ratio, which sets the ratio of the absolute position value to mm. When the absolute position value reaches or exceeds the set position value 1, If the reaching or exceeding the Para_Pos1 and a position value _2 the absolute position value is set to output a Para_Pos2 for outputting a signal.

On the other hand, in the measurement of the dam level, a phenomenon may occur in which the water level fluctuates due to wind or waviness, or a large water level fluctuation occurs temporarily due to the start and stop of the generator, and a negative value is calculated in the discharge amount calculation. In the present invention, a method of calculating a liquid level value by applying a measured value to a digital filter in order to precisely measure a water level is used. Hereinafter, an example of such a digital filter will be described as an ideal low- An example in which a windowed-sinc filter having the characteristic of a windowed-sinc filter is applied will be described.

The signal processing method is divided into an analog filter method using a resistor, a capacitor, a coil, and a digital filter method implementing a filter function by a program of a processor. The digital filter method includes a method of calculating in a time domain and a method of calculating a frequency domain Frequency domain). The method of calculating the digital filter method in the time domain includes an IIR method (Infinite Impulse Response Methode) and an FIR method (Finite Impulse Response Methode). The frequency domain method uses a fast Fourier transform (FFT) A windowed-sinc filter calculation method which has a relatively small amount of calculation but is easy and has excellent filter performance has been applied in a method of extracting only a frequency component of a specific region from among a plurality of frequency domain components.

Figs. 17, 18 and 19 show the characteristics of the windowed-sinc filter. The windowed sink filter has perfectly flat characteristics in the passband, But cuts off all frequencies higher than the cut-off frequency.

As a result, if the cut-off frequency of the windowed-sinc filter is appropriately set, it becomes possible to measure an accurate water level calculation value by eliminating the water surface wave caused by the wind or the swell or the temporary large water level fluctuation. The transfer function (h [i]) of this filter is expressed by the following equation, where fc represents the cut-off frequency.

In order to implement a more efficient filter function with respect to the cutoff frequency, the equation using the Blackman window is expressed by the following equation.

Where fc is the cut-off frequency, M is the filter kernel length, i is the sampling variable, 0 = i = M, and K is the unity gain constant. The relationship between the band width BW for the cutoff frequency f _C and the number of filter samples M is expressed by the following equation.

FIG. 17 shows the characteristics of a filter having a windowed-sinc filter cut-off frequency F _C of 0.0015 Hz and a sampling number M of 600.

First, the value of H [i] / SUM obtained by dividing the value of H [i] by the sum of the values of H [i] / SUM is calculated by substituting the value of i from -300 to 300 in the above equation .

Since the unity gain constant K must be designed so that the output signal remains unchanged even when the frequency is zero, that is, even when the DC input signal is constant and the infinite time elapses, the sum of all the filter constants should be 1.0 Is a constant that divides the values of H [i] by SUM (sum of all), that is, H (i) / SUM.

By multiplying the measured water level value by the coefficient of H [i] / SUM sequentially, and then integrating all of these values, the water level value at which the filter is applied can be obtained.

(A) of Figure 18 are simplified to show the value calculated by substituting the value of i to _{sin (2π · f c · i} ) from -300 to 300 in the graph, (b) is a final H rough a set of calculated [ i] / SUM is displayed in a graph.

FIG. 19 is an example of simulating a case where the water surface shakes virtually in order to test the characteristics of a window deck filter to be applied. It is assumed that a small wave occurs due to wind, and three signals having different cycles and amplitudes (Pd) of two positive (+) direction and two (Pd) negative (-) directions were assumed assuming that the generator started and suddenly fluctuates suddenly or doubled. , The water level value to be tested (input_val) is expressed by the following equation.

In FIG. 19, the operation result of the windowed-sinc filter is denoted by 'SINC filter output' and the operation result of the IIR filter is denoted by 'IIR average value' as another operation example.

In more detail, simulation was performed assuming that the water level fluctuates frequently due to wind and swell, and that a large disturbance of 20 cm due to the start and stop of the generator occurs for 5 seconds. When the window deck filter is applied, It is possible to calculate a very stable water level value having a water level variation of only 3 cm.

As described above, the liquid level measuring apparatus according to the present invention calculates the absolute position of the float 157 moving according to the change of the water level through the absolute displacement meter 100 and the liquid level measuring controller 200, So that it can be measured. In addition, by applying the measured value to a windowed-sinc filter, which is a digital filter, it is possible to calculate a stable water level value even when the water level is suddenly changed.

It is to be understood that the present invention is not limited to the above-described embodiment, and that various modifications and changes may be made by those skilled in the art without departing from the spirit and scope of the appended claims. Of course, can be achieved.

100: absolute displacement meter 103: bearing
104: rotating shaft 105: rotating shaft gear
106: reduction gear 107a: first gear
107b: second gear 107c: third gear
112: precision encoder 113: wide-angle encoder
123: DC 24V power supply 130: notebook computer
131: LCD & Key board 132: Upper monitor A
133: host controller B 134: optical signal converter
135: upper monitoring device C 136: antenna
150: liquid level detecting device 151: timing belt pulley
152: Belt pressing bearing 153: Freezing heater
154: Coupling 155: Bearing support
156: Temperature control device 157: Float
158: timing belt 160: wireless communication section
161: Balance weight 162: Zero point adjustment device
163: Zero setting bracket 164: Zero setting side
166: Zero setting leveler 167: Temperature and humidity sensor
168: Space heater 183: Reference bottom surface
184: Belt winding spring 185: Belt winding gear A
186: Belt winding gear B 187: Belt winding pulley
200: liquid level measurement controller 201: microprocessor
202: USB port 203: FRAM memory
204: Precision encoder interface unit 206: Wide encoder interface unit
208: DC / DC converter 209: RS-232C communication unit
210: RS-485 communication unit 211: liquid level output unit
212: limit signal output unit 213: optical signal transmission /
214: Ethernet communication unit 215: Wireless transmission /

Claims (13)

A float 157 which floats on the liquid surface and moves up and down according to the change of the liquid level; A timing belt pulley 151 for transferring a vertical movement amount of the float 157 through a timing belt 158 and converting the amount of rotation into a rotation amount; A precision encoder 112, which is an absolute encoder for precise measurement, provided on a rotary shaft 104 to which the rotation amount of the timing belt pulley 151 is transmitted, measures and outputs a value corresponding to the rotation angle of the rotary shaft 104; Which is an absolute encoder for wide-range measurement, provided on the reduction gear shaft and measuring and outputting a value corresponding to the reduced rotation angle, A displacement meter (100); And a liquid level measurement controller (200) for calculating an absolute position value of the float (157) by analyzing an output value of the absolute displacement meter (100) and calculating a liquid level value according to an absolute position of the calculated float A level measuring apparatus comprising:
The liquid level measurement controller 200 calculates the rotation speed of the precision encoder 112 using the value of the wide angle encoder 113 and calculates the resolution of the precision encoder 112 to the rotation speed of the calculated precision encoder 112 And then adding the value of the measured precision encoder 112 to calculate the absolute position value of the float 157,
The liquid level measurement controller 200 checks the precision encoder rotation number calculation table 420 in which the step-up lower limit value, the step-up upper limit value and the down step-band value are set for each revolution of the precision encoder 112, The table index value in the range in which the value of the wide-angle encoder 113 is greater than or equal to the step-up lower limit value of the precision encoder rotation speed calculation table 420 and smaller than the step-up upper limit value is set as the rotation speed of the precision encoder 112 Step correction is performed by subtracting 1 from the set number of revolutions of the precise encoder 112 when the value of the wide encoder 113 is smaller than the value of the down step_band value and the value of the precise encoder 112 is larger than the down step lower limit value, And calculates the number of revolutions of the encoder (112).
delete delete delete The method according to claim 1,
A float 157 is connected to one end of a timing belt 158 for transmitting the up and down movement amount of the float 157 to the timing belt pulley 151 and a counter weight 157 for balancing the weight with the float 157 is connected to the other end. 161,
Timing belt pressing bearings 152 for pressing the timing belt 158 to prevent the timing belt 158 from being disengaged from the timing belt pulley 151 due to a sudden change in the water level are provided on both sides of the timing belt pulley 151 The level of the liquid level is measured.
The method according to claim 1,
A freezing prevention heater 153 and a temperature control device 156 are provided on the side surface of the timing belt pulley 151 to prevent the timing belt 158 from freezing on the timing belt pulley 151 during the winter season, And the temperature of the pulley (151) and the timing belt (158) is kept constant.
The method according to claim 1,
The absolute displacement meter 100 and the liquid level measuring controller 200 are installed in the liquid level detecting device 150 and a zero point setting bracket for setting the zero point of the liquid level is provided on one side of the liquid level detecting device 150, A zero point setting horizon 166 extending in the horizontal direction of the liquid level detecting device 150 is installed at one side of the zero point setting bracket 163,
The value obtained by subtracting the size of the zero point setting bracket 163 from the height difference between the reference bottom surface 183 as the liquid level reference and the upper surface of the zero point setting horizon 166 is measured through the LCD & Is input to the controller 200 and is set as the zero point of the float 157,
Wherein the zero point of the float (157) is set by setting the zero point of the LCD & Key board (131) in a state where the float (157) touches the bottom surface of the zero point setting bracket (163).
8. The method of claim 7,
A height difference between the reference floor 183 and the upper surface of the zero point setting horizon 166 is defined as H1 and the height of the reference floor 183 is referred to as H0, 166 and the zero-point setting surface 164 is " H2, "
The altitude value H3 of the zero point setting surface 164 is calculated as H3 = H0 + H1-H2 and input to the memory of the liquid level measurement controller 200 via the LCD & Key board 131,
When the zero point is set through the LCD & Key board 131 in a state where the float 157 rises and comes into contact with the zero point setting surface 164, the float 157 is set to the value 'H3'
And the water level Hw is calculated as Hw = H3 - H4 when the float 157 moves to the position of H4.
The method according to claim 1,
A float 157 is connected to one end of a timing belt 158 for transmitting the up and down movement amount of the float 157 to the timing belt pulley 151 and a timing belt winding device for winding the timing belt 158 is connected to the other end However,
The timing belt winding apparatus includes a belt winding pulley 187 for winding a timing belt 158, a belt winding spring 184 for providing power for winding the timing belt 158, a belt winding pulley 187, And a belt winding gear (185) (186) connecting between the belt winding springs (184).
The method according to claim 1,
The liquid level measurement controller 200
A precision encoder interface unit 204 to which a measurement signal is inputted from the precision encoder 112,
A wide-angle encoder interface 206 for receiving a measurement signal from the wide-angle encoder 113,
And a microprocessor 201 for receiving and analyzing the precise encoder measurement signal and the wide-angle encoder measurement signal through the precision encoder interface unit 204 and the wide-area encoder interface unit 206 to calculate an absolute water level value Liquid level measuring device.
11. The method of claim 10,
The microprocessor 201
A windowed-sinc filter using a Blackman window is applied to correct the slope of the water surface and to calculate the exact level of the liquid level. The cut-off frequency is filtered out from the measured values. The windowed-sinc filter ) Is set to a cut-off frequency (fc) through a transfer function (h [i]) through the following equation.
[Mathematical Expression]

(Where fc is the cut-off frequency, M is the filter kernel length, i is the sampling variable 0 = i = M, and K is the unity gain constant)
(A) in which the amount of movement of the float (157) that moves up and down in accordance with the change of the liquid level is lifted through the timing belt (158) and the timing belt pulley (151); The precision encoder 112, which is an absolute encoder for precise measurement coupled to a rotation shaft 104 to which the rotation amount of the timing belt pulley 151 is transmitted, measures a value according to the rotation angle of the rotation shaft 104, (B); A value corresponding to the rotation angle decelerated by the reduction gear 106 is measured by the wide-angle encoder 113, which is an absolute encoder for wide-range measurement, provided in the reduction gear 106 that reduces the rotation speed of the rotation shaft 104, (C) inputting to the measurement controller 200; The rotation speed of the precision encoder 112 is calculated using the value of the wide angle encoder 113 measured by the liquid level measuring controller 200 and the resolution of the precision encoder 112 (D) calculating the absolute position value of the float by adding the value of the measured precision encoder 112 and measuring the liquid level value according to the calculated absolute position of the float, As a method,
The liquid level measurement controller 200 checks the precision encoder rotation number calculation table 420 in which the step-up lower limit value, the step-up upper limit value and the down step-band value are set for each revolution of the precision encoder 112, The table index value in the range in which the value of the wide-angle encoder 113 is equal to or greater than the step-up lower limit value of the precision encoder rotation speed calculation table 420 and smaller than the step-up upper limit value is set as the rotation speed of the precision encoder 112 Step correction is performed by subtracting 1 from the set number of revolutions of the precise encoder 112 when the value of the wide encoder 113 is smaller than the value of the down step_band value and the value of the precise encoder 112 is larger than the down step lower limit value, And the number of revolutions of the encoder (112) is calculated. delete

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