CN104132622B - Distributed optical fiber deformation tensile instrument and test method - Google Patents

Abstract

The invention relates to a distributed optical fiber deformation and stretching instrument, in particular to a deformation and stretching device aiming at the practical application ability and simulating practical application of optical fibers in different stretching states. The distributed optical fiber deformation stretcher includes a stretching system and an optical fiber carrying platform; the stretching system is connected with the optical fiber carrying platform. It solves the shortcomings of the conventional optical fiber deformation tensile test device that cannot be simple, accurate and monitors the performance of distributed optical fiber sensing under multiple working conditions. This test device can simply and effectively control the loading progress. The platform can carry out basic application research on simulating crack opening development, small strain monitoring, and variable angle and variable elevation multi-working conditions, avoiding the problems of low survival rate of optical fiber, long model making cycle, poor effect and high cost in some indoor simulation tests, and further It can study the deformation mechanism and combination mechanism of distributed optical fiber monitoring technology under complex load conditions and various working conditions.

Description

A Distributed Optical Fiber Deformation Tensile Instrument and Testing Method

technical field

The invention relates to a distributed optical fiber deformation and stretching instrument and a testing method, in particular to a deformation and stretching device aiming at the practical application ability of the optical fiber in different stretching states and simulating the practical application.

Background technique

As a new type of sensing technology, distributed optical fiber sensing technology has been expanding its application fields. The good sensing performance of optical fiber is a necessary condition to ensure the health monitoring of optical fiber structure. The tensile deformation of optical fiber is the key to the reliability of sensing performance of distributed optical fiber monitoring system. important indicators. Due to the poor survival rate of optical fiber in actual engineering applications due to the performance of the material itself, it is impossible to track and observe the process of deformation and damage of optical fiber in its actual application. The lack of comprehensiveness, accuracy and timeliness in its analysis and research due to simplicity and other reasons. Therefore, efficient and accurate repeatable tests and convenient simulation of complex environments with multiple working conditions are an extremely critical core technology for the study of distributed optical fibers. It is necessary to design a Smaller, precise and easy-to-control deformation and stretching equipment.

With the development of miniaturization and distribution of structural health monitoring technology, its ability to monitor small deformation of structures has been paid more and more attention. At present, the tensile servo testing machine for optical fiber is expensive, complicated to operate, takes up a lot of space, and can only perform a single material performance tensile test. It is difficult to accurately perform a tensile test with monitoring capabilities, especially it cannot simulate multiple working conditions in practical applications. The deformation process of optical fiber hinders more basic research and application promotion. At this stage, the equipment and testing technology for diversified, systematic, and multi-working-condition precise tensile tests are still blank.

Contents of the invention

The present invention provides a distributed optical fiber deformation and stretching instrument and a testing method for the above-mentioned deficiencies.

The present invention adopts following technical scheme:

A distributed optical fiber deformation stretcher according to the present invention includes a stretching system and an optical fiber carrying platform; the stretching system is connected to the optical fiber carrying platform;

The stretching system includes: front supporting steel plate, movable steel plate, rear supporting steel plate, connecting horizontal column, handle connection plate, rotating handle, fixed horizontal column, scale, threaded rotating horizontal column; the front supporting steel plate and the rear supporting The steel plates are vertically arranged to connect the horizontal column and the fixed horizontal column. There is a movable steel plate between the front supporting steel plate and the rear supporting steel plate; Connection, the other end is provided with a rotating handle, and the rotating handle is connected to the threaded rotating horizontal column through the handle connection plate; the connecting horizontal column is provided with a scale;

The optical fiber bearing platform includes: a scaled steel column, an adjustable angle placement table, a tension end fixture, and a fixed end fixture; the scaled steel column is arranged on the top of the rear support plate, and the top of the rear support plate is also set There are fixed end clamps; the adjustable angle placing table is arranged on the top of the movable steel plate, and the adjustable angle placing table is equipped with a tensile end clamp, and the optical fiber is placed between the tensile end clamp and the fixed end clamp.

In the distributed optical fiber deformation and stretching instrument of the present invention, the fixed end fixture is sleeved on the scaled steel column, and slides along the extension direction of the scaled steel column.

According to the distributed optical fiber deformation and stretching instrument of the present invention, the adjustable angle placement table is composed of a graduated disk and a threaded steel column; a threaded steel column is arranged under the graduated disk, and the A plurality of scale holes are arranged on the surface of the disc, and the scale holes are arranged along the circumference with the center of the scale disc as the center.

The distributed optical fiber deformation and extensometer of the present invention also includes a measuring room; the measuring room is arranged on the front supporting steel plate.

In the distributed optical fiber deformation and stretching instrument of the present invention, a thermometer protection layer is provided in the measuring room, the thermometer is fixed and protected in the measuring room, and the pointed screw rod with spring is pressed by pressing the measuring room bolt cap. The pressure is placed in the threaded buckle, which drives the rotation and closure of the door panel of the measuring chamber.

In the distributed optical fiber deformation stretcher according to the present invention, the stretching end fixture includes a stretching end fixture support table, a second threaded steel column, a stretching end fixture rotating a horizontal column, and a stretching end fixture turning hand; with scale One type optical fiber clamp; the support platform of the tensile end clamp is provided with a groove, and two pieces of optical fiber clamp one with scale are arranged in the groove, and the horizontal column of the tensile end clamp rotates from the two sides of the support platform of the tensile end clamp. The end extends into the groove and is respectively connected with the first graduated optical fiber clamp. The tensile end clamp rotating cross column is provided with a tensile end clamp rotating hand; the lower end of the tensile end clamp support table is provided with a threaded steel column two.

In the distributed optical fiber deformation and stretching instrument of the present invention, the fixed end fixture includes: a steel plate pinch, a pinch bolt, a fixed section fixture rotating a horizontal column, a fixed section fixture rotating handle, a graduated optical fiber fixture two, and a fixed End fixture support platform; fixed end fixture support platform is equipped with a boss in the center, and a groove is arranged in the boss, and a graduated optical fiber fixture is arranged in the groove. One end of the rotating horizontal column of the fixed section fixture is connected with the second end of the graduated optical fiber fixture, and the other end is arranged with a rotating handle of the fixed section fixture; two legs extend from the bottom end of the fixture support platform at the fixed end, and the two ends of the two legs are equipped with steel plate buckles. The buckle is fixed to the fixture support table at the fixed end by the buckle bolt.

The test method of the distributed optical fiber deformation stretcher, the test steps are as follows:

Step 1: Assembling and debugging equipment construction and adjusting the height and angle of the fixed end fixture 13 and the tension end fixture 8;

Step 2: According to the initial gauge length of the optical fiber to be stretched in the test and the scale on the scaled connecting horizontal column, turn the rotating handle to rotate the threaded rotating horizontal column to the same length as the initial gauge length;

Step 3: Arrange the optical fiber to be stretched in the fixed end fixture and the tensile end fixture according to the test purpose, keep the tensile end fixture and the fixed end fixture horizontal, and rotate the handle of the tensile end fixture and the fixed end fixture its trimming is fixed;

Step 4: Connect the stretched fiber to the fiber deformation monitor based on the pre-pumped Brillouin optical time domain analysis technology, and apply the tensile load according to the test requirements;

Step 5: Record the temperature change in the test through the measurement room. For the situation where the temperature influence cannot be ignored, such as the ambient temperature difference is too large or the room needs to be kept in a stretched state for a long time, it can be combined with the temperature change of the optical fiber monitored by the measurement room. The optical fiber temperature influence coefficient determines the optical fiber strain value caused by the environmental temperature change, and then deducts the influence of the external temperature on the optical fiber to realize the optical fiber temperature compensation process.

Step 6: Turn the rotating handle to drive the threaded rotating horizontal column to rotate, and then drive the movable steel plate platform to move through the threaded rotation, and then drive the movement of the tensile end clamp, so that the optical fiber will be stretched and deformed accordingly;

Step 7: Use the temperature measurement room to monitor the temperature results, based on the optical fiber Brillouin frequency shift change and temperature is related to the change, and has a good linear relationship, expressed as , which can be written as ,in, , is the Brillouin frequency shift when the temperature is T and T ₀ , is the Brillouin temperature coefficient, That is, the change value of the temperature of the stretched section of the optical fiber of the specimen, is the change in Brillouin frequency shift caused by temperature change; the above formula can be used to calculate the Brillouin frequency shift value of the optical fiber caused by the external temperature at this time, and then according to It can be concluded , so that it can be concluded that , it can finally be obtained that , and finally calculate the deformation value caused by the external tensile load, where, is the variation of Brillouin frequency shift due to temperature and strain changes, is the change in Brillouin frequency shift caused by the strain change, is the strain factor, is the induced strain value.

Beneficial effect

The invention solves the disadvantage that the conventional optical fiber deformation tensile test device cannot monitor the performance of distributed optical fiber sensing simply and accurately under multiple working conditions. The stretching platform can carry out basic application research of simulating crack opening development, small strain monitoring, and variable angle and variable elevation multi-working conditions, avoiding the problems of low survival rate of optical fiber, long model making cycle, poor effect and high cost in some indoor simulation tests , and then can study the deformation mechanism and combination mechanism of distributed optical fiber monitoring technology under complex load conditions and various working conditions, which can be extended to practical engineering applications.

Using this test instrument combined with pre-pumped Brillouin distributed optical fiber sensing technology to realize the small strain and micro strain monitoring of the structure, with the help of the device of the present invention, it is of great significance for various researches such as distributed optical fiber performance, and it is lightweight , Handy, low manufacturing cost, less external interference, many working conditions can be combined, wide range of use and other advantages.

Description of drawings

Fig. 1 is the front view of deformation stretching device of the present invention;

Fig. 2 is a detailed structural diagram of an angle-adjustable placement table in the deformation and stretching device of the present invention;

Fig. 3 is a detailed structure diagram of the stretching end fixture in the deformation stretching device of the present invention;

Fig. 4 is a detailed structure diagram of the measuring room in the deformation and stretching device of the present invention;

Fig. 5 is a detailed structure diagram of the fixture at the fixed end in the deformation and stretching device of the present invention.

In the figure, 1 is the front supporting steel plate platform; 2 is the movable steel plate platform; 3 is the rear supporting steel plate platform; 4 is connecting the horizontal column; 5 is the bolt cap of the horizontal column; Placement platform; 8 is the tension end fixture; 9 is the handle connecting plate; 10 is the rotating handle; 11 is the horizontal column for fixing; 12 is the scale; 13 is the fixture for the fixed end; 14 is the measuring room; 15 is the horizontal column for fixing Bolt cap; 16 is a threaded rotating horizontal column; 17 is an angled disc, 18 is a threaded steel column 1; 19 is a threaded steel column 2; 20 is a rotating horizontal column of a tensile end clamp; 21 is a tensile End clamp rotating handle; 22 is a graduated optical fiber clamp; 23 is a supporting platform for tensile end clamp; 24 is a bolt cap for measuring chamber; 25 is a spring; 26 is a pointed screw; 27 is a protective layer for a thermometer; 28 is a thermometer ; 29 is a buckle with thread; 30 is a steel plate buckle; 31 is a pinch bolt; 32 is a pinch bolt cap; 33 is a rotating horizontal column of the fixed end fixture; 34 is a rotating handle of the fixed end fixture; 35 is a graduated optical fiber Fixture two; 36 is a fixed end fixture support platform; 37 is an optical fiber to be stretched, and 40 is a measuring chamber door panel.

Detailed ways

Below in conjunction with accompanying drawing, the present invention is described in further detail:

As shown in the figure: a distributed optical fiber deformation stretcher and testing method, it is composed of two parts: a stretching system and an optical fiber bearing platform, wherein the main components of the stretching system are: front support steel plate 1, movable Steel plate 2, rear supporting steel plate 3, connecting horizontal column 4, horizontal column bolt cap 5, handle connection plate 9, rotating handle 10, fixing horizontal column 11, scale 12, fixing horizontal column bolt cap 15, threaded rotating horizontal column 16 etc.;

The main components of the optical fiber bearing platform are: steel column with scale 6, adjustable angle placing table 7, fixed end fixture 13, tensile end fixture 8, etc.; front supporting steel plate 1, movable steel plate 2 and rear supporting steel plate 3 Round holes of different sizes are distributed, and the connecting horizontal column 4 and the graduated connecting horizontal column 12 respectively traverse the top round holes of the front supporting steel plate 1, the movable steel plate 2 and the rear supporting steel plate 3, and use the fixed horizontal column 11 to The front supporting steel plate 1 and the rear supporting steel plate 3 are connected, and the cross column bolt cap 5 and the fixed cross column bolt cap 15 are used to fix them respectively, and the front supporting steel plate 1 and the movable steel plate 2 are connected by a threaded rotating horizontal column 16, with The threaded rotating horizontal column 16 is connected with the rotating handle 10 through the handle connection plate 9, and the adjustable angle placing table 7 and the graduated steel column 6 are respectively fixed on the movable steel plate 2 and the rear supporting steel plate 3, and the optical fiber to be stretched 37 is placed at the tensile end clamp 8 and the fixed end clamp (13).

Each component can be freely assembled and disassembled to facilitate replacement and further modification tests. For the adjustable angle type placing platform 7, it can be replaced with other types of placing platforms when other tests require, in order to prepare for the different requirements of various tests. The scaled connecting horizontal column 12 is used to mark the basic physical size of the optical fiber 37 to be stretched.

This test device can not only test the horizontal optical fiber stretch, but also can test the inclined stretch at different elevations. The steel plate buckle 30 of the fixed end clamp 13 is connected to the graduated steel column 6 through a buckle bolt 31 , and is fixed with a buckle bolt cap 32 . The scaled steel column 6 can be stretched obliquely at different elevations according to different fixed positions, and the position where the fixed end clamp 13 contacts the rear supporting steel plate platform 3 is the horizontal stretching place of the optical fiber.

The test device can also perform tensile tests on optical fibers in different directions. The angle-adjustable placement table 7 is provided with 8 angled round holes marked 0~360° with an interval of 45°, and a central round hole is set at the center of the disk, which is the horizontal stretching position of the optical fiber. Adjustable angle type placement table 7 is made up of angled type disc 17 and threaded steel column-18. For the requirements of different tests, the tensile end fixture 8 can be fixed to round holes at different angles through the threaded steel column 2 19. It can simulate the local horizontal stretching or possible deformation and stretching state of different inclined directions and different angles in the actual application of optical fibers.

The distance between the movable steel plate 2 and the rear support steel plate 3 is adjusted to realize the simulation of the crack monitoring process. However, the traditional method of laying optical fibers in it by making a model to monitor cracks has problems such as unrepeatability of a single test piece, long model making cycle, and high cost. The distance between the movable steel plate 2 and the rear support steel plate 3 is calibrated in advance by using the connecting horizontal column 12 with a scale, and it is used as the initial value of the crack, and when the distance is opened by turning the handle 10, the continuous expansion of the crack to the optical fiber can be simulated. The process of being broken and destroyed by the excessive opening of the crack, combined with the use of the adjustable angle placing table 7, can simulate the deformation mechanism of the optical fiber when it traverses the crack at different angles.

The test device can monitor the change of ambient temperature by using the measuring room 14 . When analyzing and calculating the tensile strain of the optical fiber, the monitoring results of the measuring room 14 can be used as temperature compensation calculations. The thermometer protection layer 27 fixes and protects the thermometer 28 in the measuring room 14, and presses the pointed screw 26 with the spring 25 into the threaded buckle 29 by pressing the measuring room bolt cap 24, driving the measuring room door panel 40 The rotation and closure of it can protect and isolate the measuring chamber 14.

The fixed end clamp 13 of this test device is different from the tensile end clamp 8. For the fixed end clamp 13, it is a fixed end clamp support table 36 with a certain height and is externally connected with a graduated optical fiber clamp 2 35, and the handle is rotated by the fixed end clamp. 34 Rotate the fixture at the fixed end to rotate the horizontal column 33 to fine-tune its width, and the inner surface of the outer scaled optical fiber fixture 2 35 is grooved and the center scale is marked. The stretching end fixture 8 is placed with a graduated optical fiber fixture 22 through the stretching end fixture support platform 23, and the stretching end fixture is rotated by the turning handle 21 of the stretching end fixture to rotate the horizontal column 20 to fine-tune its width, and through the threaded steel column 2 19 it is fixed on the angled disc 17. the

In this embodiment, the SMF-28e ordinary single-mode fiber will be used as the fiber 37 to be stretched as an example, and the test method for the deformation behavior of the distributed fiber under the condition of deformation and stretching is tested:

Step 1: Assembling and debugging equipment construction and adjusting the height and angle of the fixed end fixture 13 and the tension end fixture 8 .

Step 2: According to the initial gauge length of the optical fiber 37 to be stretched in the test and the scale on the graduated connecting horizontal column 12, turn the rotating handle 10 to rotate the threaded rotating horizontal column 16 to a length consistent with the initial gauge length .

Step 3: arrange the optical fiber 37 to be stretched in the fixed end fixture 13 and the stretching end fixture 8 according to the test purpose, keep the stretching end fixture 8 and the fixed end fixture 13 horizontally, and turn the handle 21 and The fixed end clamp rotates the handle 34 to fix it with fine adjustment.

Step 4: Connect the port of the stretched optical fiber 37 to the optical fiber optical information collection device, and apply a tensile load according to the set test requirements;

Step 5: Record the temperature change in the test through the measuring chamber 14 , and the temperature compensation effect needs to be considered in the case of a large temperature difference or a test that needs to be kept in a stretched state for a long time in the room.

Step 6: Turn the rotating handle 10 to drive the threaded rotating horizontal column 16 to rotate, and then drive the movable steel plate platform 2 to move through the threaded rotation, and then drive the movement of the tensile end clamp, so that the optical fiber will be stretched and deformed accordingly. The fiber monitoring technology of pre-pumped Brillouin optical time domain analysis monitors its tensile deformation.

Step 7: Use the measurement room 14 to monitor the temperature results, based on the optical fiber Brillouin frequency shift change and temperature is related to the change, and has a good linear relationship, expressed as , which can be written as ,in, is the change in Brillouin frequency shift due to temperature change, , Divided into temperature and the initial temperature The magnitude of the Brillouin frequency shift under, is the temperature coefficient, That is, the temperature change value of the stretched section of the optical fiber of the test piece. The above formula can be used to calculate the Brillouin frequency shift value of the optical fiber caused by the external temperature at this time, and then according to It can be concluded , so that it can be concluded that , and finally calculate the deformation value caused by the external tensile load, where is the strain factor, is the induced strain value.

As stated above, while the invention has been shown and described with reference to certain preferred embodiments, this should not be construed as limiting the invention itself. Various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (7)

1. A distributed optical fiber deformation stretcher, characterized in that: comprise a stretching system, an optical fiber carrying platform; said stretching system is connected with the optical fiber carrying platform; The stretching system includes: front supporting steel plate (1), movable steel plate (2), rear supporting steel plate (3), connecting cross column (4), handle connecting plate (9), rotating handle (10), fixing horizontal column ( 11), scale (12), threaded rotating horizontal column (16); the vertically arranged connection horizontal column (4) and the fixed horizontal column ( 11), there is a movable steel plate (2) between the front supporting steel plate (1) and the rear supporting steel plate (3); the threaded rotating horizontal column (16) runs through the front supporting steel plate (1), and the threaded rotating horizontal column (16 ) is threadedly connected to the movable steel plate (2), the other end is provided with a rotating handle (10), and the rotating handle (10) is connected to the threaded rotating horizontal column (16) through the handle connection plate (9); the connecting horizontal column ( 4) There is a scale (12) on it; The optical fiber bearing platform includes: a steel column with scale (6), an adjustable angle placement platform (7), a tension end clamp (8), and a fixed end clamp (13); the steel column with scale (6) Arranged on the top of the rear supporting steel plate (3), the top of the rear supporting steel plate (3) is also provided with a fixed end clamp (13); the fixed end clamp (13) is sleeved on the graduated steel column (6), along the belt The scaled steel column (6) slides in the extension direction; the adjustable angle placing platform (7) is arranged on the top of the movable steel plate (2), and the adjustable angle placing platform (7) is equipped with a tensile end clamp (8), An optical fiber (37) is placed between the tensile end clamp (8) and the fixed end clamp (13). 2. The distributed optical fiber deformation and extensometer according to claim 1, characterized in that: the adjustable angle placement platform (7) consists of a scaled disc (17) and a threaded steel column (18) ; The threaded steel column (18) is arranged below the scale disc (17), and several scale holes are arranged on the scale disc (17). The scale holes are centered on the band scale disc (17). Arranged along the circumference of the center. 3. The distributed optical fiber deformation extensometer according to claim 1, characterized in that it further comprises a measuring room (14); the measuring room (14) is arranged on the front supporting steel plate (1). 4. The distributed optical fiber deformation and stretching instrument according to claim 3, characterized in that: a thermometer protective layer (27) is provided in the measuring chamber (14) to fix and protect the thermometer (28) in the temperature measuring chamber (14). In the chamber (14), press the pointed screw (26) with the spring (25) into the threaded buckle (29) by pressing the bolt cap (24) of the measuring chamber to drive the door panel (40) of the measuring chamber Turn to close. 5. The distributed optical fiber deformation extensometer according to claim 1, characterized in that: the tensile end clamp (8) includes a tensile end clamp support platform (23), a threaded steel column two (19), The tensile end clamp rotates the horizontal column (20), the tensile end clamp rotates the handle (21); a graduated optical fiber clamp (22); the tensile end clamp support platform (23) is provided with grooves, concave There are two graduated optical fiber clamps (22) in the groove, and the rotating horizontal column (20) of the tensile end clamp extends into the groove from the two ends of the tensile end clamp support platform (23) and is connected with the graduated optical fiber respectively. Fixture one (22) is connected, and the tension end fixture rotation cross column (20) is provided with a tension end fixture rotation handle (21); the lower end of the tension end fixture support platform (23) is provided with a threaded steel column two (19) . 6. The distributed optical fiber deformation and stretching instrument according to claim 1, characterized in that: the fixed end fixture (13) includes: a steel plate buckle (30), a pinch bolt (31), and the fixed end fixture rotates Horizontal column (33), rotating handle of fixed end fixture (34), scaled optical fiber fixture two (35), fixed end fixture support platform (36); fixed end fixture support platform (36) is provided with a boss in the center, boss There is a groove inside, and a graduated optical fiber clamp (35) is arranged in the groove. The fixed end clamp rotating horizontal column (33) extends into the groove in the boss, and one end of the fixed end clamp rotating horizontal column (33) is connected with the belt Scale-type optical fiber clamp two (35) is connected, and the other end is arranged with the rotating handle (34) of the fixed end clamp; the bottom end of the fixed end clamp support table (36) extends two legs, and the two ends of the two legs are provided with steel plate buckles (30 ), the steel plate buckle (30) is fixed by the buckle bolt (31) and the fixture support platform (36) at the fixed end. 7. the test method of distributed optical fiber deformation stretcher as claimed in claim 1, is characterized in that: test step is as follows: Step 1: Assembling and debugging equipment construction and adjusting the height and angle of the fixed end clamp (13) and the tensile end clamp (8); Step 2: According to the initial gauge length of the optical fiber (37) to be stretched in the test and the scale on the connecting horizontal column (4) with scale (12), turn the rotating handle (10) to rotate the threaded rotating horizontal column (16 ) to the same length as the initial gauge length; Step 3: Arrange the optical fiber to be stretched (37) in the fixed end fixture (13) and the stretched end fixture (8) according to the test purpose, keep the stretched end fixture (8) and the fixed end fixture (13) horizontally, And it is fine-tuned and fixed by the rotating handle (21) of the tensile end clamp and the rotating handle (34) of the fixed end clamp; Step 4: Connect the port of the stretched optical fiber (37) to the optical fiber optical information collection device, and apply a tensile load according to the set test requirements; Step 5: Record the temperature change in the test through the measuring room (14). For situations where the temperature influence cannot be ignored, such as the difference in ambient temperature is too large or the room needs to be kept in a stretched state for a long time, it can be monitored according to the temperature in the measuring room (14). The optical fiber temperature change is combined with the optical fiber temperature influence coefficient to determine the optical fiber strain value caused by the environmental temperature change, and then the influence of the external temperature on the optical fiber is deducted to realize the optical fiber temperature compensation process; Step 6: Turn the rotating handle (10) to drive the threaded rotating horizontal column (16) to rotate, and then drive the movable steel plate platform (2) to move through the threaded rotation, and then drive the movement of the tensile end clamp, so that the optical fiber is pulled accordingly Stretch deformation; Step 7: Use the measuring room (14) to monitor the temperature results, according to the formula Finally, the deformation value caused by the external tensile load is calculated; in, is the variation of Brillouin frequency shift due to temperature and strain changes, is the change in Brillouin frequency shift due to temperature change, is the strain factor, is the induced strain value; T is the temperature.