JP2003075461A - Anemometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anemometer that can measure both the direction and velocity of a wind without being exposed to neither rain nor snow even when the anemometer is used outdoors by combining a wind velocity sensor with temperature sensors and, in addition, designing a shelter covering the sensors. SOLUTION: This anemometer 1 is provided with an air course pipe 2 having a measuring air course 5 communicating with the outdoor air through both opened ends 3 and 4 inside and the wind velocity sensor 6 composed of a temperature-dependent resistance element arranged in the air course 5. The velocity of the wind can be measured by detecting the resistance value of the sensor 6 which changes in accordance with the velocity of the wind when the sensor is cooled by the wind. The direction of the wind is discriminated by arranging two temperature sensors 7a and 7b on both sides of the sensor 6, with one of the sensors 7a and 7b being positioned in the slip stream Wf of the wind passing through the sensor 6, and comparing the measured values of the sensor 7a and 7b with each other. The air course pipe 2 works as the shelter which protects the sensors 6, 7a, and 7b from rain drops.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wind direction anemometer capable of measuring both wind direction and wind speed.
In particular, the present invention relates to an anemometer suitable for outdoor wind direction measurement such as air pollution measurement at a roadside site.

[0002]

2. Description of the Related Art In recent years, roadside air pollution caused by automobile exhaust gas, particularly health damage caused by fine particulate matter (polluting particles with a particle size of 2.5 μm or less), has become a problem. Surveys are being planned. The characteristics of roadside air pollution are that the pollution concentration varies greatly depending on the location and that it is easily affected by the local wind system. Therefore, when measuring air pollution at such roadside sites, it is desirable to arrange the measurement points as many and densely as possible. Therefore, in order to meet the demand for grasping the actual condition of roadside air pollution, a high-density and high-time-resolution type monitoring system using a particle sensor that is inexpensive and easy to handle is being developed. However, despite the fact that the pollution concentration is easily affected by the local wind system as described above, the development of an inexpensive, small and lightweight wind anemometer for the field observation has been delayed, and still Large, heavy and expensive anemometers are used. And, especially regarding the measurement of the wind speed, almost no detailed measurement near the ground is performed.

Conventionally, as a measuring instrument for measuring the wind speed outdoors, a cup-type / propeller-type anemometer or an ultrasonic anemometer has been used. The former anemometer measures the wind speed by the rotational speed of the wind when the wind mechanically rotates the cup or propeller. This kind of anemometer
It has been used for a long time for meteorological observation, etc. due to its simple operation principle and excellent durability, but the response of the rotation speed to the change of wind speed is poor due to the weight of the rotating part, and the measuring instrument itself is also large. heavy.

On the other hand, the latter ultrasonic anemometer utilizes the property that the propagation speed of sound waves changes depending on the wind speed. That is, the ultrasonic wave transmitter and the ultrasonic wave receiver are set apart from each other by a predetermined distance, and the wind speed is obtained from the difference in arrival time of the sound waves that changes depending on the wind speed. In such an ultrasonic anemometer, the speed of sound changes depending on the temperature, so it is necessary to correct the measured value, but since there is no moving part, there is no mechanical delay and the response is fast. Is a feature. In addition, since only the wind velocity component on the line connecting the transmitter and the receiver is measured, a total of three coordinate components of horizontal two components + vertical component (mainstream direction and horizontal component vertical thereto, and vertical component) are independently measured ( Three-dimensional measurement) is possible. Therefore, the ultrasonic anemometer is often used for academic meteorological observation. However, since the distance between the transmitter and the receiver cannot be shortened so much to measure the wind speed with high accuracy, the measuring instrument as a whole tends to be large (about 50 cm in total) and is generally expensive. Is.

Other types of anemometers include hot wire anemometers,
Some of the thermistor anemometers, germanium anemometers, etc., use a temperature-dependent resistance element in the sensing part. In these anemometers, the sensing unit is set to 250 to 300 by applying a current to the element.
The wind speed is measured by utilizing the resistance change when heated to ℃ and cooled by being hit by the wind. Since the sensitivity of such anemometer changes depending on the temperature, temperature compensation is necessary for the measured value. The sensing part is small and has good response characteristics, but it is weak against water and cannot be used outdoors. Therefore, these anemometers can be used to measure airflow in wind tunnels and rooms.
It is mainly used only for indoor experiments. In addition, these anemometers have a problem that the wind directions cannot be discriminated because they have sensitivity to the wind from any wind direction.

[0006]

As described above, in the conventional anemometer, the mechanical anemometer has a large weight, and the response of the measurement is slow with respect to the change of the wind speed, and the handling is inconvenient. In addition, there are problems such as large size and high cost. On the other hand, there is a problem with the electrical measurement that not only the wind direction cannot be discriminated but also the outdoor measurement cannot be used depending on weather phenomena such as rain and snow.

Therefore, in the present invention, by combining a wind speed sensor and a temperature sensor and devising a shelter that covers these sensors, both the wind direction and the wind speed can be outdoors even without being exposed to rain or snow. Making measurable is a problem to be solved.

That is, it is an object of the present invention to provide an inexpensive, small and lightweight wind direction anemometer capable of performing detailed monitoring of the wind direction and speed without getting wet with rain or snow even at an outdoor observation site. Is.

[0009]

In order to achieve this object, according to the present invention, an air passage tube having a measurement air passage inside which communicates with the outside air through both open ends, and a temperature arranged in the measurement air passage. An anemometer consisting of a wind resistance sensor consisting of a dependent resistance element, and two temperature sensors arranged in the measurement wind path with the wind speed sensor sandwiched between the wind speed sensor and one of which is located in the wake of the wind passing through the wind speed sensor. Is configured.

According to the wind direction and anemometer thus constructed, when the wind of the outside air flows in from any one of the opening ends and flows through the measurement air passage of the air passage tube, the wind speed sensor used in the heated state is used. The temperature-dependent resistance element is cooled by the wind, and the resistance value changes. The change in the resistance value is larger as the wind speed is higher. Therefore, by detecting the resistance value, the wind speed in the measurement wind path can be measured. The measured value of one of the temperature sensors arranged before and after in the longitudinal direction of the air passage tube with the wind speed sensor sandwiched between the measured values of the other temperature sensor by entering the wake of the heated wind speed sensor. Since it becomes a high value, by comparing the measured values of both temperature sensors, it can be discriminated from which open end the wind entering is blowing, that is, the wind direction. The measured value of the other temperature sensor is used for temperature compensation of the measurement by the temperature-dependent resistance element. Moreover, by arranging the wind speed sensor and the temperature sensor inside the air duct, the air duct serves as a shelter for protecting these sensors from raindrops.

In this wind direction anemometer, the air passage tube is
A straight tube whose both open ends directly open to the outside air can be used. By using a straight tube that directly opens to the outside air as described above, the simplest wind direction and anemometer with which the flow in the internal measurement air path is made uniform is constructed.

Further, in this wind direction anemometer, a main air duct having a main air duct which is open to the outside through both open pipe ends is used, and the air duct is the main air duct whose measurement air duct is the main air duct. It is also possible to connect to the main air duct tube in such a manner as to connect at two positions spaced apart in the longitudinal direction. In the wind direction and anemometer having such a configuration, the wind that has flowed into the main wind passage flows into the measurement wind passage that is partially bypassed with respect to the main wind passage, and the wind direction wind speed is measured in the measurement wind passage. Moreover,
Even if the main air duct is installed in the vertical direction, raindrops and snowflakes do not enter the air duct, so it is possible to measure the vertical wind direction and speed even in bad weather.

In such an anemometer in which the air duct is connected to the main air duct, the main air duct is provided at an intermediate position between two positions of the main air duct to which the air duct is connected. It is preferable to provide a control valve for controlling the amount of air flowing through the main air passage.
By doing so, by controlling the opening degree of the control valve, it is possible to change the ratio between the air volume flowing through the main air duct and the air volume flowing into the measured air duct of the air duct as the bypass duct. For example, when the wind is light, the control valve is fully closed or in a state close to it to increase the amount of air flowing into the measurement air passage of the air passage tube, and when the wind is strong, the control valve is fully opened or close to it. By doing so, the amount of air flowing into the measurement air passage of the air passage tube can be reduced. Therefore, even in a situation where the wind speeds are significantly different, the wind speed sensor only needs to operate in an appropriate wind speed range. Since the relationship between the wind speed and the measured value is obtained in advance using the opening of the control valve as a parameter, the wind speed of the outside air can be obtained by appropriately calculating the measured value according to the opening of the control valve.

Further, in such anemometer, guide vanes having variable projecting amounts from the open pipe ends can be provided at both open pipe ends of the main air duct. If the guide vanes are provided at both ends of the main air duct as described above, the wind of the outside air is guided by the guide vanes and easily flows into the main air duct. Moreover, since the amount of protrusion of the guide vane from the open pipe end is variable,
Since the amount of air flowing into the main air duct is adjusted by changing the amount of protrusion according to the strength of the wind, the output of the wind speed sensor and the wind speed range can be balanced.
Since the relationship between the wind speed and the measured value is obtained in advance using the guide vane protrusion amount as a parameter, the wind velocity of the outside air is obtained by appropriately calculating the measured value according to the guide vane protrusion amount.

In such anemometer, the temperature-dependent resistance element is preferably a thermistor or germanium. When the wind hits the heated resistance element that is the sensing unit, the heat of the resistance element is taken by the wind, and the temperature of the resistance element decreases and the resistance value changes, but as such a temperature-dependent resistance element, , A thermistor or germanium.

The anemometer can be used as two sets which are orthogonal to each other in two dimensions or three sets which are orthogonal to each other in three dimensions. In that case, the two-dimensional or three-dimensional wind direction and speed of the outside air are calculated based on the directional characteristics that follow the cosine curve of the angle between the wind direction of each anemometer and the longitudinal direction of the wind duct or main wind duct. To be done. That is, if the cross-sectional shape of the air duct or the main duct as a shelter is set appropriately, the measured value of the wind speed sensor will be the cosine curve (cosine curve) with respect to the measured value when facing the wind. Will have a directional characteristic that roughly follows. Therefore, for example, if the wind pipe is a straight pipe that opens directly to the outside air, raindrops may enter the wind pipe, so under bad weather conditions, measure the two-dimensional (planar) wind direction and speed. In that case, when the open end of the air duct is not directly facing the wind, the vector having each of the measured values of the two sets of anemometers that are orthogonal to each other by the directional characteristics according to the above cosine curve is used. The wind direction and speed can be determined as. If the air duct is a bypass pipe connected to the main air duct, there is no risk of raindrops entering the air duct, so measure the three-dimensional (three-dimensional) wind direction and speed in bad weather. Can also be used for Even in that case,
When the open pipe end of the main wind duct does not directly face the wind, the wind direction and wind speed are determined as a vector whose components are the measured values of the three sets of anemometers that are orthogonal to each other due to the directional characteristics according to the above cosine curve. Can be set.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an anemometer according to the present invention will be described below with reference to the accompanying drawings. In the figure,
2 is a schematic view showing an embodiment of an anemometer according to the present invention with a part thereof broken, and FIG. 2 is an explanatory view for explaining the definition of a found area in the anemometer shown in FIG.

FIG. 1 shows a basic conceptual embodiment of the anemometer according to the invention. This anemometer 1
A straight tubular air passage tube 2 having both open ends 3 and 4 in which a measurement air passage 5 is formed, and a sensor group arranged in the measurement air passage 5 are provided. The sensor group includes a wind speed sensor 6 and two temperature sensors 7a and 7b arranged in the longitudinal direction of the wind passage tube 2 with the wind speed sensor 6 interposed therebetween, that is, before and after the direction of the wind flowing in the wind passage tube 2. And consists of. The temperature sensors 7a and 7b are sensors used for measurement of the wind direction and temperature compensation of the wind speed sensor 6, and may have the same configuration. Wind speed sensor 6 and temperature sensor 7
a and 7b are wires 8 and 9 for taking out signals, respectively.
a and 9b are connected, penetrate the air duct tube 2 and are connected to an external instrument. In the illustrated example, the wires 8, 9a, 9b are individually extended from the respective sensors 6, 7a, 7b, but the sensor group is collectively referred to as the sensor unit U in the air duct tube 2. The air duct tube 2 can be made to be attachable and the wires 8, 9a, 9b can also be bundled and penetrated.

One of the temperature sensors 7a and 7b (in the illustrated example, the temperature sensor 7b) is provided at a position that enters the heat wake Wf of the heated wind velocity sensor 6. In consideration of the case where the wind direction is opposite, the other temperature sensor 7a is also provided at the position where the wind speed sensor 6 enters the heat wake at that time. The temperature measured value by the temperature sensor 7b in the heat wake Wf is higher than the temperature measured value by the temperature sensor 7a located on the windward side. Therefore, the temperature sensors 7a, 7
By comparing both measured values by b, it can be seen that the wind is flowing from the temperature sensor side with the lower measured value toward the temperature sensor side with the higher measured value, and the wind direction can be discriminated. . For temperature compensation of the wind speed sensor 6, a measurement value by a temperature sensor (in the illustrated example, the temperature sensor 7a) that is located on the windward side of the wind speed sensor 6 and is not affected by other sensors is used.

Compared with the case where either one of the open ends 3 and 4 of the air duct 2 is in direct opposition to the wind W (wind direction θ = 0 °),
When the direction of the air duct 2 with respect to the wind W is inclined as shown in FIG. 2, the wind velocity in the air duct 2 is the found area of the opening area of the open end 3 of the air duct 2 as seen from the main wind direction (projection). Area) S (= S
₀ × cos θ, S ₀ : opening area of the air passage tube 2, θ: air passage tube 2
It is considered to be approximately proportional to the angle between the central axis C and the wind direction. That is, as the directional characteristic of the wind speed sensor 6,
The shape of the air passage tube 2 is set so that the air volume that flows into the air passage tube 2 with respect to the air volume that flows into the air passage tube 2 when facing directly follows a roughly cosine curve.

By arranging the air ducts 2 in two orthogonal horizontal directions, it is possible to measure the wind velocity for each wind direction component (two-dimensional measurement).
By arranging in line with the axis (two orthogonal horizontal directions + vertical direction), it is possible to measure the wind speed for each wind direction component (three-dimensional measurement). A conceptual diagram of two-dimensional measurement using such anemometer 1 is shown in FIG. The two anemometers 1a and 1b are arranged in a plane orthogonal state, and the reference line x of the wind W
When the angle with respect to is θ, the anemometers 1a, 1b
Let w ₁ and w ₂ be the measurement values measured by respectively, and from the directional characteristics in the y direction, the y-direction facing component Wcos (π /
2-θ) = W sin θ = w ₂ , and therefore, the wind W is a vector such that the component in the reference line x direction is w ₁ and the component in the reference line y direction orthogonal to the reference line x is w _2. It is the required wind. Further, the wind direction θ is arctan (w ₂ / w ₁ ).

In this wind direction anemometer 1, the wind speed sensor 6 is made of a thermistor or germanium having a negative temperature resistance coefficient. That is, the sensing unit has a characteristic that the resistance value decreases / rises as the temperature rises / falls, and the wind speed is measured by making use of the characteristic. However,
Due to such characteristics, if moisture adheres to the sensing portion of the wind speed sensor 6, the reliability of the measured value will be lost. Therefore, the sensitive portion of the wind speed sensor 6 needs to be protected from being wet by raindrops and the like, and the sensitive portion of the wind speed sensor 6 is protected from rainwater by the air duct 2 that functions as a shelter.

In the case of this wind direction anemometer 1, as shown in FIG. 2, depending on the wind direction angle, a strong local negative pressure is generated on the leeward end face of the air passage tube 2 due to a vortex or separation flow. ,
Therefore, it is expected that the desired directional characteristics will be lost. Further, when the wind anemometer 1 is arranged vertically, the air duct 2
Each of the sensors 6 and 7 gets wet through the open end 3 or 4 of the above. Therefore, as shown in FIG. 3, an improved anemometer 10 was devised while maintaining the basic configuration of the anemometer 1 shown in FIG. 3 is a cutaway plan view showing an improved embodiment of the wind direction anemometer according to the present invention, and FIG. 4 is a side view of the wind direction anemometer shown in FIG. In the embodiments shown in FIGS. 3 and 4, the same components as those used in the embodiments of FIGS. 1 and 2 are given the same reference numerals as those shown in FIGS. 1 and 2. Therefore, redundant description will be omitted.

Referring to FIG. 3 and FIG. 4, the anemometer 10 has a thick main air duct 11 having a diameter of about 50 mm in which a main air duct 15 is formed, and a long main air duct 11 is provided. An air passage pipe 12 having a diameter of about 20 mm is provided as a bypass pipe for the main air passage pipe 11 at two locations separated in the direction. The main air duct 11 is a straight pipe, and the main air duct 15 formed inside has open pipe ends 13, 14 at both ends.
It is open to the outside through. The air duct 12 is a pipe which has a measurement air duct 16 inside and is bent in a U shape as a whole, and the open ends 17 and 18 of the air duct 12 are orthogonal to the side wall 19 of the main air duct 11. Open to the condition, and thereby the measurement air duct 16
Is always connected to the main air duct 15. A sensor group (sensor unit U) including a wind speed sensor 6 similar to that shown in FIG. 1 and temperature sensors 7 a and 7 b for wind direction discrimination and temperature compensation extends in parallel with the main air duct 11. It is arranged in the portion of the measurement air duct 14.

A butterfly type control valve 20 is provided in the main air passage 15 at an intermediate position between the both ends of the air passage pipe 12. Now, it is assumed that either one of the open pipe ends 13 and 14 of the main wind passage 15 is placed to face the wind W. The flow of the wind W passes through the main wind passage 15 from the windward side to the leeward side, but the air flow rate can be adjusted by the tilt angle α of the control valve 20 arranged at the center of the main wind passage 15, and the measurement wind passage can be adjusted accordingly. 1
The flow rate through 6 is also adjusted. For example, the tilt angle α of the control valve 20 is parallel to the central axis C of the main air duct 11 (the tilt angle α
= 90 °), the air volume in the main air passage 15 becomes maximum,
Almost no wind flows in the measurement air duct 16. On the other hand, the control valve 20
Of the main air duct 11 at a right angle (α = 0
If the temperature is set to °), the main air passage 15 is closed and the flow rate of the air flowing through the measurement air passage 16 becomes maximum.

The directional characteristics when the main wind duct 11 is placed obliquely to the main wind direction have already been described with reference to FIG. 2, but in the case of this wind direction anemometer 10, the opening pipe is used. Guide vanes 21 and 22 capable of projecting and retracting in parallel with the main air passage 15 are installed at the ends 13 and 14, respectively. The guide vanes 21, 22 appear and disappear when the opening pipe end 13,
It is possible by sliding along the pair of grooves 23, 23 formed inside 14. Therefore, when the main air duct 11 is placed obliquely to the main wind direction,
The guide vanes 21 and 22 are the open pipe ends 1 of the main air duct 11.
By changing the dimension L protruding from the outsides 3 and 14, the amount of air flowing into the main air passage 15 can be adjusted. In this way, by adjusting the tilt angle α of the control valve 20 and the protruding dimension L of the guide vanes 21 and 22,
The use range of the anemometer 10 can be changed according to the situation at the measurement site. The wind speed of the outside air to be measured, the gas flow velocity in the measurement air passage 16 measured by the sensor unit U, the tilt angle α of the control valve 20, and the protruding dimension L of the guide vanes 21 and 22 have a functional relationship with each other. It is obtained in advance as a map or a relational expression. The wind speed of the outside air is controlled by the control valve 2
The tilt angle α of 0 and the protrusion dimension L of the guide vanes 21 and 22 are used as parameters, and are obtained from the measurement values measured by the sensor unit U based on a map or a relational expression that is obtained in advance.

This anemometer 10 is used when installed horizontally.
Of course, even when installed vertically, the sensor unit
Let U never get wet with rainwater. That is, the main air duct
When one open pipe end 13 or 14 of 11 is directed upward
However, the raindrops that have fallen from the open pipe end 13 or 14 are mainly
Flow into the measurement air duct 16 that opens to the side wall 19 of the air duct 11.
There is no waste. Therefore, as shown in FIG.
Wind anemometers 10a, 10b, 10c along three orthogonal axes.
By arranging it, regardless of the weather, practical use
Used as an outdoor anemometer for three-dimensional measurement with high accuracy
be able to. Anemometers 10a, 10b, 10c
Each measured value is w₁, W_Two, W_ThreeThen the wind
As for W, the component in each direction of the reference lines x, y, z is w.₁, W_Two, W
_ThreeIt is a wind that is sought as a vector such that I
The wind direction of the wind W is the angle θ as shown in FIG.₁, Θ_Twoso
If there is, Wcos θ_Twocos θ₁= W₁ Wcos θ_Twosin θ₁= W_Two Wsinθ_Two= W_Three Then, solving these simultaneous equations, the angle θ₁, Θ_TwoIn the wind
A direction is required. In addition, W^Two= W₁ ²+ W_Two ²+ W_Three ² Is.

[0028]

Since the anemometer according to the present invention is constructed as described above, it has the following effects. That is, this anemometer is a measurement air passage that communicates with the outside air through both open ends of the air passage tube, and a wind speed sensor that consists of a temperature-dependent resistance element and measures the wind speed of the gas flowing through the measurement air passage,
Since two temperature sensors are arranged with the wind speed sensor sandwiched so that one of them is located in the wake of the wind passing through the wind speed sensor, the wind of the outside air flows in from one of the open ends. When flowing through the measurement wind passage of the passage pipe, the wind velocity of the gas flowing through the measurement wind passage is measured by detecting the resistance value that the resistance element used in the heated state is cooled and changes. Since the measured value of one temperature sensor entering the wake of the wind speed sensor is higher than the measured value of the other temperature sensor, the wind direction is discriminated by comparing the measured values of both temperature sensors. By arranging the wind speed sensor and the temperature sensor in the air duct, the air duct serves as a shelter for protecting these sensors from raindrops, so that the wind sensor according to the present invention is used outdoors. In addition, it is possible to perform detailed monitoring of the wind direction and speed without getting wet with rain or snow at the observation site. Further, since this wind direction and wind speed sensor is configured not by mechanical measurement but by combining a wind speed sensor and a temperature sensor, it can be made small and lightweight and can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of an anemometer according to the present invention with a part thereof cut away.

FIG. 2 is an explanatory diagram illustrating the definition of a found area in the wind direction anemometer shown in FIG.

FIG. 3 is a cutaway plan view showing another embodiment of the anemometer according to the present invention.

4 is a side view of the anemometer shown in FIG.

FIG. 5 is an explanatory view of a use state showing a state where the anemometer according to the present invention is two-dimensionally arranged.

FIG. 6 is an explanatory view of a usage state showing a state in which the anemometers according to the present invention are three-dimensionally arranged.

[Explanation of symbols]

1,10 Wind direction anemometer 2,12 wind pipe 3,4,17,18 Open end 5,16 Measuring wind path 6 Wind speed sensor 7a, 7b Temperature sensor 11 Main air duct 13,14 Open pipe end 15 Main wind path 20 control valve 21,22 guide vanes α tilt angle L protrusion amount

Claims (7)

[Claims] 1. An air passage tube having a measurement air passage therein, which communicates with the outside air through both opening ends, a wind speed sensor including a temperature-dependent resistance element arranged in the measurement air passage, and one of which includes the wind speed sensor. An anemometer consisting of two temperature sensors arranged in the measurement wind passage with the wind speed sensor interposed therebetween in a manner positioned in the wake of the passing wind. 2. The wind direction anemometer according to claim 1, wherein the air duct is a straight pipe whose both open ends are directly opened to the outside air. 3. A main air duct having therein a main air duct opened to the outside through both open pipe ends, wherein the measurement air duct is separated from the main air duct in the longitudinal direction thereof. The wind direction anemometer according to claim 1, characterized in that the wind direction anemometer is connected to the main air duct tube in such a manner as to be connected at the two positions. 4. The main air duct, at an intermediate position between the two positions of the main air duct to which the air duct is connected,
The wind direction anemometer according to claim 3, further comprising a control valve for controlling an amount of air flowing through the main air passage. 5. A guide vane having a variable amount of projection from each of the opening pipe ends is provided at each of the opening pipe ends of the main air duct, and the guide vanes are provided. Wind direction anemometer. 6. The wind direction anemometer according to claim 1, wherein the temperature-dependent resistance element is a thermistor or germanium. 7. The anemometer is used as two sets that are orthogonal to each other in two dimensions or three sets that are orthogonal to each other in three dimensions. Anemometer as described in paragraph.