KR20050030426A - An apparatus for controling the constant feed of raw material in sinter machine - Google Patents

Abstract

To provide an apparatus for controlling constant feed of raw material for sintering heat source, wherein the apparatus improves quality of product, prevents damage and breakdown of facilities, solves safety accident fundamentally and reduces environmental pollution due to SOx and NOx by preventing abnormality of components due to abnormal feed of coke and anthracite raw material. In an apparatus for controlling constant feed of raw material for sintering heat source comprising two feed hoppers(35A,35B), two feed belts(41A,41B), load cells(21,22) and pulse generators(23,24), the apparatus further comprises: a first detection value operation part(110) for multiplying a weight value of coke on the feed belt(41A) by a speed value of motor(33); a second detection value operation part(210) for multiplying a weight value of anthracite on the feed belt(41B) by a speed value of motor(34); a first set value control part(120) for providing a first interlocking set value and a set value selection signal according to deviation between detection values of the first detection value operation part and a preset first single set value; a second set value control part(220) for providing a second interlocking set value and a set value selection signal according to deviation between detection values of the second detection value operation part and a preset second single set value; a first set value selection part(130) for selecting the first single set value or the first interlocking set value according to the set value selection signal by the first set value control part; a first feed control part(140) for controlling operation of the motor(33) according to deviation between the set value selected by the first set value selection part and the detection values by the first detection value operation part; a second set value selection part(230) for selecting the second single set value or the second interlocking set value according to the set value selection signal by the second set value control part; and a second feed control part(240) for controlling operation of the motor(34) according to deviation between the set value selected by the second set value selection part and the detection values by the second detection value operation part.

Description

AN APPARATUS FOR CONTROLING THE CONSTANT FEED OF RAW MATERIAL IN SINTER MACHINE}

The present invention relates to a quantitative cutting control device for raw materials for sintering heat source, in particular by controlling to detect and correct abnormal cutting factors occurring in the process of cutting the coke and anthracite raw material, thereby preventing component abnormalities due to abnormal cutting, etc. Quantitative sintering heat source can improve quality, prevent downtime, damage and breakdown of equipment, fundamentally solve safety hazards such as narrowing, and reduce environmental pollution by SOx and NOx It relates to a cutout control device.

In general, the sintering process is shown in Figure 1, the coke and anthracite coal cut out from the iron ore bin is quantitatively cut out in a CFW (Constant Feed Weigher) and then mixed in a drum mixer and installed in the top of the sintering machine It is stored in the mixing raw material bin and continuously supplies the mixing raw material mixed with coke, anthracite coal, etc., and is then supplied with air and COKE OVEN GAS from the ignition furnace to ignite the upper surface of the mixing raw material and sinter. It is a process of manufacturing a sintered ore by melt-bonding the blended raw materials while sucking air into the exhaust gas pipe through approximately 25 wind phases in the lower direction.

2 is a control block diagram of a raw material cutting device of a conventional sintering process.

Referring to FIG. 2, the conventional quantitative cutting device is a device that continuously cuts raw materials under various conditions according to a set value (1, 2) of a predetermined compounding ratio, which is a mechanical device (DEVICE) and a control panel (CONTROL PANEL). The mechanical device may include a feed hopper 35, a gate gate amp 36, a side skirt board 37, a tail pulley 38, and a belt tensioning weight. It consists of a roller 39, a take-up block 40, a feeder belt 41, and the like, and the control panel includes motors 33 and 34 for cutting, load cells 21 and 22, and pulse generators. (P / G) (23, 24), thyristor (31, 32), and the like.

Briefly explaining the cutting amount calculation by the conventional raw material cutting device, first, the raw material discharged from the cutting gate 36 to the outside is loaded on the feeder belt 41 and passes through the metering roller to load cell (LOAD CELL) ( The weights of raw materials such as coke and anthracite coal are detected by 21 and 22, and the detected signal mV is calculated with the speed of the cutting belt BELT to calculate the cutting amount PV.

In addition, referring to Figure 2, the cutting raw materials such as coke, anthracite coal, etc., the current signal corresponding to the set value (1, 2) (SV) is input to the cutting control means 1, 2 (3, 4), the section The output MV of the output control means 1, 2 (3, 4) is input to the set value SV of the thyristors 31 and 32, and thus to the cutting motors 33 and 34. The raw material is cut out by supplying a voltage corresponding to the set value SV to rotate the cutting motors 33 and 34. The belt speed detected at this time is calculated with the weight detection signals detected by the load cells 21 and 22 to calculate the instantaneous cutting amount. This is again inputted to the cutout control means 1, 2 (3, 4) as the measured value PV and compared with the set value (1, 2) (SV), and the deviation is controlled again by repeating the above process.

However, in the case of unfavorable raw material conditions in a quantitative cutting device using coke and anthracite raw materials, afterglow of the raw material is caught in the load cells 21 and 22, or the raw material on the belt is abnormally caused by lumping. As a result, the raw material load is not properly detected by the load cells 21 and 22, which causes the measured value PV to be relatively smaller than the set value SV, thereby increasing the deviation. The output MV of the means 1, 2 (3, 4) is increased to be input to the setpoint of the thyristors 31, 32 to repeat the process of supplying a higher voltage to the motor.

When this process is repeated, the motors 33 and 34, which are supplied with high voltage, rotate at the maximum speed. In this case, raw material cutting corresponding to the set value SV is not performed. In addition to the adverse effects, the load cells 21 and 22, the pulse generators P and G 23 and 24, and the motors 33 and 34, which detect the load of the raw materials, are overloaded. There is a problem that occurs a situation that results in the resulting burnout, shortening the life.

In addition, as described above, the coke and anthracite used as the main heat source of sintering is directly connected to the sintered state, for example, when the coke and the anthracite are less mixed with the amount of the coke and the anthracite used as a blending raw material, The surface ignition is not made properly, so that even if the raw material is not available even if supplied as a post-process, there is a problem that unnecessary work such as yard (YARD) is placed. On the contrary, if excessive cutting is made and mixed with the blended raw materials, the surface of the raw material is fused (excessive melting) when the surface is ignited by ignition, so that the ventilation is poorly ventilated to the lower part of the raw material or the red blood mine (the excessive heat source is contained during the sintering Normal sintered ore production, such as sintered ore in a state of being present) is not made.

In this way, the cutting state of the sintered heat source coke and anthracite coal should immediately be quantitatively cut out according to the proper usage cost to influence the quality of the sintered ore. More importantly, this phenomenon has a problem of causing environmental pollution due to deterioration of product quality and increase of SO x , NO x, etc., in the operation of the raw material, an increase in the fuel unit required for production.

The present invention has been proposed to solve the above problems, the object of which is to control the early detection and correction of abnormal cutting factors occurring in the process of cutting the coke and anthracite raw material, thereby preventing component abnormalities due to abnormal cutting Raw material for sintered heat source which can improve quality, prevent operation interruption, prevent damage and breakdown of equipment, fundamentally solve safety disasters such as narrowing, and reduce environmental pollution by SOx, NOx, etc. To provide a metering control device.

In order to achieve the above object of the present invention, the raw material quantification control device for sintering heat source of the present invention

Two feed hoppers for storing coke and anthracite, two feeder belts each driven by a motor for transporting and cutting raw materials from the respective feed hoppers, a load cell for detecting the weight of the raw material on the feeder belt, respectively; In the raw material quantification control device for sintering heat source comprising a pulse generator for detecting the speed of the motor,

A first detection value calculator for multiplying the coke weight on the feeder belt by the load cell with the speed value of the motor by the pulse generator;

A second detection value calculator for multiplying the anthracite weight value on the feeder belt by the load cell with the speed value of the motor by the pulse generator;

A first set value controller configured to provide a first interlocking set value and a set value selection signal according to a deviation between the detected value by the first detected value calculator and a first set value set in advance;

A second set value controller configured to provide a second interlocking set value and a set value selection signal according to a deviation between the detected value by the second detected value calculator and a second preset single set value;

A first set value selector configured to select one of the first single set value and the first interlocked set value according to a set value select signal by the first set value control part;

A first cut-out control unit controlling the operation of the motor in accordance with a deviation between the set value selected by the first set value selecting unit and the detected value by the first detected value calculating unit;

A second setting value selection unit for selecting one of the second single setting value and the second interlocking setting value according to a setting value selection signal by the second setting value control unit; And

A second cut-out control unit that controls the operation of the motor in accordance with a deviation between the set value selected by the second set value selecting unit and the detected value by the second detected value calculating unit;

Characterized in having a.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings referred to in the present invention, components having substantially the same configuration and function will use the same reference numerals.

3 is a block diagram of a quantitative cutting control device for the raw material for sintering heat source according to the present invention.

Referring to Figure 3, the raw material quantification control device for sintering heat source according to the present invention is driven by two feed hoppers (35A, 35B) and the motor (33, 34) for storing the coke and anthracite coal, respectively Two feeder belts 41A and 41B for carrying and cutting raw materials from the hoppers 35A and 35B, load cells 21 and 22 for detecting the weights of the raw materials on the feeder belts 41A and 41B, respectively, It is applied to an apparatus for cutting sintered raw materials including pulse generators 23 and 24 for detecting the speeds of the motors 33 and 34, respectively.

The sintering heat source raw material quantification control device of the present invention is calculated by multiplying the coke weight value on the feeder belt 41A by the load cell 21 and the speed value of the motor 33 by the pulse generator 23. Multiplying the first detection value calculation unit 110, the anthracite weight value on the feeder belt 41B by the load cell 22, and the speed value of the motor 34 by the pulse generator 24. Providing a first interlocking setting value and a setting value selection signal according to a deviation between a detection value by the second detection value calculating unit 210 and the first detection value calculating unit 110 and a preset first single setting value. Providing a second interlocking setting value and a setting value selection signal according to a deviation between a detection value by the first setting value control unit 120 and the second detection value calculating unit 210 and a preset second single setting value. A set value by the second set value controller 220 and the first set value controller 120 A first set value selector 130 selecting one of the first single set value and the first interlocked set value according to a selection signal, and a set value selected by the first set value selector 130 and the first set value; Selection of the set value by the first cut-out control unit 140 and the second set value control unit 220 to control the operation of the motor 33 in accordance with the deviation from the detected value by the first detection value calculating unit 110. A second setting value selecting unit 230 for selecting one of the second single setting value and the second interlocking setting value according to a signal, and a setting value selected by the second setting value selecting unit 230 and the second setting value; A second cut-out control unit 240 for controlling the operation of the motor 34 in accordance with the deviation from the detection value by the detection value calculation unit 210.

The first setting value control unit 120 corrects a deviation between a first single setting value previously set and a detection value by the first detection value calculating unit 110 according to a preset first correction curve. A first interlocking setting unit 122 for providing a first interlocking setting value by adding up the calculation unit 121, the first single setting value and the deviation value by the second setting value control unit 220, and the first interlocking setting unit 122. And a first upper and lower limit comparator 123 which provides a set value selection signal according to whether the deviation value by the deviation calculator 122 is outside a preset range (upper limit, lower limit).

The first deviation calculator 121 calculates a calculator c (121A) for calculating a deviation (c) between a first single set value (a) [SV] and a detected value (b) [PV], and the calculator 1 (121A). And a proportioner 1 (121B) for correcting the deviation (c) calculated in the through the first correction curve corresponding to the amount of heat.

The sintering heat source raw material quantification control device for the first alarm unit 17 to alert the deviation of the upper limit and the lower limit in accordance with the set value selection signal from the first upper and lower limit comparison unit 123 of the first set value control unit 120. It further includes.

The second set value controller 220 corrects a deviation between a second single set value previously set and a value detected by the second detection value calculator 210 according to a preset second correction curve. A second interlocking setting unit 222 that adds the second single setting value and the deviation value by the first setting value control unit 120 to provide a second interlocking setting value; And a second upper and lower limit comparator 223 for providing a set value selection signal depending on whether the deviation value by the deviation calculator 222 is outside a preset range (upper limit, lower limit).

The second deviation calculator 221 is configured to calculate a deviation i between a second single set value g, SV, and a detected value h, PV, and the calculator 2, 221A. And a proportioner 2 (221B) for correcting the deviation (i) calculated in) through the second correction curve corresponding to the amount of heat.

The sintering heat source raw material quantification control device is a second alarm unit 18 for warning the deviation of the upper limit and the lower limit in accordance with the set value selection signal from the second upper and lower limit comparison unit 223 of the second set value control unit 220. It further includes.

4A and 4B are diagrams illustrating first and second correction curves of the proportioners 1 and 2 of the present invention, and FIG. 4A is a diagram showing correction curves of the proportioner 1 121B of the present invention and FIG. An illustration of the correction curve of proportioner 2 (221B).

Hereinafter, the operation and effects of the present invention will be described in detail with reference to the accompanying drawings.

According to the present invention, each of the single set values SV set in advance at the time of raw material cutting are input to the set values SV of the first and second cutout controllers 130 and 230, respectively, and the outputs MV corresponding to each set value SV are obtained. ) Is transmitted to the motors [33, 34] through the thyristors (31, 32) and rotates to make raw material cutting in proportion to the quantitative cutting control process applied to the raw material cutting. 3 and 4A and 4B will be described.

Referring to FIG. 3, the first detection value calculating unit 110 of the sintering heat source raw material quantitative control apparatus according to the present invention includes a coke weight value on the feeder belt 41A and a pulse generator 23 by the load cell 21. It multiplies the speed value of the motor 33 by. The second detection value calculator 210 of the present invention multiplies the anthracite weight value on the feeder belt 41B by the load cell 22 by the speed value of the motor 34 by the pulse generator 24. That is, the weight signal [mV] and the pulse generator 23 measured by the load cells 21 and 22 in the TOTALIZER 29 and 30 of the first and second detection value calculators 110 and 210. And the speed signal PULSE obtained by (24) are respectively integrated.

Then, the first set value control unit 120 of the present invention is the first interlocking set value and the set value according to the deviation between the detected value by the first detection value calculating section 110 and the first set value set in advance. In addition, the second set value controller 220 according to the present invention may provide a selection signal according to a deviation between the detected value by the second detected value calculator 210 and the preset second independent set value. Provides set value and set value selection signal.

The first set value controller 120 will be described in detail. The first deviation calculator 121 of the first set value controller 120 may include a first single set value and a first set value for cutting coke. The deviation from the detection value by the detection value calculating unit 110 is corrected according to a preset first correction curve, and the first interlocking setting unit 122 of the first setting value control unit 120 sets the first single setting. A value and a deviation value by the second set value controller 220 are added to provide a first interlocking set value, and the first upper and lower limit comparator 123 of the first set value controller 120 provides the first interlocked set value. The set value selection signal is provided according to whether the deviation value by the deviation calculator 122 is out of a preset range (upper limit value, lower limit value).

Here, the calculator 1 (121A) of the first deviation calculator 121 calculates the deviation (c) between the first single set value (a) [SV] and the detected value (b) [PV], and The proportioner 1 121B of the first deviation calculator 121 corrects the deviation c calculated by the calculator 1 121A through a first correction curve as shown in FIG. 4A corresponding to the heat amount.

In addition, when the second set value controller 220 is described in detail, the second deviation calculator 221 of the second set value controller 220 may include a second single set value for cutting anthracite and a predetermined value. The deviation from the detection value by the second detection value calculator 210 is corrected according to a preset second correction curve. In addition, the second interlocking setting unit 222 of the second setting value control unit 220 adds the second single setting value and the deviation value by the first setting value control unit 120 to obtain a second interlocking setting value. to provide. The second upper and lower limit comparator 223 of the second set value controller 220 determines whether the deviation value by the second deviation calculator 222 is outside a preset range (upper limit, lower limit). Accordingly provides a set value selection signal.

Here, the calculator 2 (221A) of the second deviation calculator 221 calculates the deviation (i) between the second single set value g [SV] and the detected value h [PV]. The proportioner 2 221B of the deviation calculator 221 corrects the deviation i calculated by the calculator 2 221A through a second correction curve as shown in FIG. 4B corresponding to the amount of heat.

Next, the first setting value selector 130 of the present invention selects one of the first single setting value and the first interlocking setting value according to the setting value selection signal by the first setting value control unit 120. It is provided to the first cut-out control unit 140. At this time, the first cut-out control unit 140 according to the deviation between the set value selected by the first set value selection unit 130 and the detected value by the first detection value calculation unit 110, the motor 33 Control the operation of

The second set value selector 230 of the present invention selects one of the second single set value and the second interlocking set value according to a set value selection signal by the second set value controller 220. It is provided to the 2 cutting-out control unit 240. At this time, the second cut-out control unit 240 according to the deviation between the set value selected by the second set value selection unit 230 and the detected value by the second detection value calculation unit 210, the motor 34 Control the operation of

Meanwhile, the first alarm unit 17 of the present invention alerts the upper and lower limit deviations in accordance with the set value selection signal from the first upper and lower limit comparator 123 of the first set value controller 120. The second alarm unit 18 of the present invention alerts the upper and lower limit deviations according to the set value selection signal from the second upper and lower limit comparator 223 of the second set value controller 220. That is, an upper limit alarm is generated when the upper limit is reached, and a lower limit alarm is generated when the lower limit is reached.

As an example, the comparison set value 19 of the first upper and lower limit comparison unit 123 is 1 [T / H], the first single set value 1 is 10 [T / H], and the first cutting agent When the input of the fisherman 140 is 12 [T / H], the deviation c between the set value a and the measured value b is +2 [T] in the calculator 1 121A of the first deviation calculator 121 at all times. / H], and is input to the ratio 1 (121B) of the first deviation calculator 121. At this time, since the deviation c between the set value a and the measured value b is +2 [T / H] in the calculator 1 121A, the set value is 1 [T] in the first upper and lower limit comparator 123. / H] is exceeded, and at the same time as the upper limit alarm, the internal logic element is operated to switch the first set value selector 130 to interlock to select the first interlocking set value.

Accordingly, the first interlocking setting value selected by the first setting value selecting unit 130 is input to the first cutoff control unit 140. In addition, the proportioner 1 (121b) of the first deviation calculator 121 multiplies the anthracite coal and the coke calorie ratio 0.88 and outputs the result, and the deviation of ± 1 [T / H] without correction until ± 1 [T / H]. In this case, the correction is performed, and as shown in the graph of FIG. 4A, a value of 1.76 [T / H], which is a value corresponding to +2 [T / H], is output and input to the second interlocking setting unit 222. In this case, the second interlocking setting unit 222 adds the second single setting value 2 and the output values of the proportioner 1 221B, and the sum value is obtained by the second setting value selecting unit 230. Optionally, the second cutout control unit 240 is set to control for anthracite quantitative cutting out.

As described above, in the case of anthracite coal, if the deviation occurs, the coke oven is corrected, and if the coke and the anthracite are simultaneously deformed or the correction control is unnecessary, the first and second set value selectors. Manual switching of the 130 and 230 is possible, so that the driver may arbitrarily manipulate and stop the correction control. Exemplary numerical values for the ratio correction shown in FIGS. 4A and 4B represent the cokes (7100 kcal / kg) and the anthracite (6300 kcal / kg) based on the calorie comparison between the coke and anthracite coal, and the present disclosure is not limited thereto. It can be changed according to the operation situation and conditions.

According to the present invention as described above, the present invention in the quantitative cutting control device for raw materials for sintering heat source, by controlling to detect and correct the abnormal cutting factors occurring in the process of cutting the coke and anthracite raw material, the abnormal cutting, etc. It can improve the quality by preventing the abnormality of components, prevent work interruption, damage and breakdown of equipment, fundamentally solve safety disasters such as narrowing, and reduce environmental pollution by SOx, NOx, etc. It has an effect.

In other words, it detects and prevents abnormal cutting out of raw materials caused by the conditions (particle size, viscosity, specific gravity, water content) and operation conditions of raw materials, thereby causing damage to equipment caused by overload, failure and damage of load cell, and afterglow removal. By eliminating problems such as stenosis safety accidents, it is possible not only to improve the amount of cut control when cutting raw materials through the quantitative cutting device, but also to improve product quality and reduce return toxic pollution factors such as SOx and NOx. It can lead to eco-friendliness and reduce raw units of fuel required for production. In addition, it is possible to efficiently manage the equipment and extend the service life of the equipment through rapid response in case of abnormal cutting.

Since the above description is only a description of specific embodiments of the present invention, the present invention is not limited to these specific embodiments, and various changes and modifications of the configuration are possible from the above-described specific embodiments of the present invention. It will be apparent to those skilled in the art to which the present invention pertains.

1 is a flowchart of a general sintering process.

2 is a control block diagram of a raw material cutting device of a conventional sintering process.

3 is a block diagram of a quantitative cutting control device for the raw material for sintering heat source according to the present invention.

4A and 4B illustrate exemplary first and second correction curves of the proportioners 1 and 2 of the present invention.

Explanation of symbols on the main parts of the drawings

17: first alarm unit 18: second alarm unit

21,22: Load cell 23,24: Pulse generator

31,32 THYRISTER 33,34: Motor

35A, 35B: Feed Hopper 36: Cutting Gate Damper

41A, 41B: feeder belt 110: first detection value calculating section

120: first set value controller 121: first deviation calculator

121A: Calculator 1 121B: Ratio 1

122: first interlocking setting unit 123: first upper and lower limit comparison unit

130: first set value selector 140: first cut-out control unit

210: second detection value calculator 220: second set value controller

221: second deviation calculator 221A: calculator 2

221B: proportioner 2 222: second interlocking setting unit

223: second upper and lower limit comparator 230: second set value selector

240: second cutout control unit

Claims (5)

Two feed hoppers 35A and 35B for storing coke and anthracite, and two feeder belts driven by motors 33 and 34 for transporting and cutting raw materials from the respective feed hoppers 35A and 35B. 41A and 41B, load cells 21 and 22 for detecting the weights of the raw materials on the feeder belts 41A and 41B, and pulse generators 23 and 24 for detecting the speeds of the motors 33 and 34, respectively. In the raw material quantification control device for sintering heat source comprising: A first detection value calculation unit (110) for multiplying the coke weight value on the feeder belt (41A) by the load cell (21) with the speed value of the motor (33) by the pulse generator (23); A second detection value calculation unit (210) for multiplying the anthracite weight value on the feeder belt (41B) by the load cell (22) and the speed value of the motor (34) by the pulse generator (24); A first set value controller 120 which provides a first interlocking set value and a set value selection signal according to a deviation between the detected value by the first detected value calculator 110 and a first set value set in advance; A second set value controller 220 for providing a second interlocking set value and a set value selection signal according to a deviation between the detected value by the second detected value calculator 210 and a second set value previously set; A first set value selection unit 130 for selecting one of the first single set value and the first interlocking set value according to a set value selection signal by the first set value control unit 120; A first cut-out control unit controlling the operation of the motor 33 according to a deviation between the setting value selected by the first setting value selecting unit 130 and the detection value by the first detecting value calculating unit 110 ( 140); A second set value selection unit 230 for selecting one of the second single set value and the second interlocking set value according to a set value selection signal by the second set value control unit 220; And A second cut-out control unit controlling the operation of the motor 34 according to a deviation between the setting value selected by the second setting value selecting unit 230 and the detection value by the second detecting value calculating unit 210 ( 240) Raw material quantification control device for sintering heat source comprising a. The method of claim 1, wherein the first set value control unit 120 A first deviation calculator (121) for correcting a deviation between a first preset single value set in advance and a detected value by the first detection value calculator (110) according to a preset first correction curve; A first interlocking setting unit 122 for providing a first interlocking setting value by adding the first single setting value and the deviation value by the second setting value control unit 220; And A first upper and lower limit comparator 123 which provides a set value selection signal according to whether the deviation value by the first deviation calculator 122 is outside a preset range (upper limit, lower limit); Raw material quantification control device for sintering heat source comprising a. According to claim 2, wherein the raw material quantification control device for sintering heat source Sintering heat source further comprises a first alarm unit (17) for warning the deviation of the upper limit and the lower limit in accordance with the set value selection signal from the first upper and lower limit comparison unit 123 of the first set value control unit 120. Raw material metering control device. The method of claim 1, wherein the second set value control unit 220 A second deviation calculator 221 for correcting a deviation between a preset second single set value and a detected value by the second detected value calculator 210 according to a preset second correction curve; A second interlocking setting unit 222 for providing a second interlocking setting value by adding the second single setting value and the deviation value by the first setting value control unit 120; And A second upper and lower limit comparator 223 which provides a set value selection signal according to whether the deviation value by the second deviation calculator 222 is outside a preset range (upper limit, lower limit); Raw material quantification control device for sintering heat source comprising a. According to claim 4, wherein the raw material quantification control device for sintering heat source Sintering heat source further comprises a second alarm unit for warning the deviation of the upper limit and the lower limit in accordance with the set value selection signal from the second upper and lower limit comparison unit 223 of the second set value control unit 220. Raw material metering control device.