An arc plasma temperature measurement method considering composite radiation

Abstract

The invention discloses a method for measuring the temperature of arc plasma considering composite radiation, belonging to the field of temperature measurement of arc plasma. First, the optical channel of a color CCD high-speed camera is calibrated by a standard radiation source, and the calibrated camera is used in cooperation with a double-peak narrowband filter to measure the arc to be measured, obtaining the.RAW file of the arc. Using the.RAW file of the arc, the radiation powers I h1 and I h2 received by the camera sensor at two central frequencies f1 and f2 are calculated, as well as their relationships with the RGB three-color values. Then, the radiation powers I h1 and I h2 received by the camera sensor from the arc to be measured are calculated by using composite radiation and bremsstrahlung. After passing through the filter for light transmission, camera photosensing, and A / D conversion, digital quantities DT1 and DT2 containing the temperature of the arc plasma are obtained. Finally, based on the colorimetric temperature measurement method, the ratio of DT1 and DT2 is taken to eliminate the unknown quantities that cannot be directly calculated in the radiation power formula, and the temperature of the arc plasma is obtained. The invention is more in line with the actual physical process and can more accurately achieve non-contact temperature measurement of arc plasma.

Description

Technical Field

[0001] The present invention belongs to the field of temperature measurement of arc plasma, and specifically relates to a method for measuring the temperature of arc plasma considering recombination radiation. Background Art

[0002] Common temperature measurement methods for arc plasma include contact temperature measurement and non-contact temperature measurement;

[0003] As a common method for contact temperature measurement, the probe temperature measurement method requires the end of the probe to be inserted into the arc plasma to be measured, which will not only have a certain impact on the structure of the arc plasma, but also cannot accurately measure the moving arc plasma.

[0004] The radiation temperature measurement method is the most commonly used method for non-contact temperature measurement. Based on the theory of thermal radiation, the radiation temperature measurement method calculates the temperature of the object to be measured through the correspondence between the radiation power of the object to be measured at certain specific frequencies and the signal output by the photodetector, and has no impact on the arc plasma structure.

[0005] Arc plasma belongs to a medium with thin optical properties and can be regarded as a completely "transparent body". Therefore, the Planck blackbody radiation formula cannot be simply applied to the temperature measurement of arc plasma, and calculations must be carried out in combination with the specific radiation process.

[0006] The main radiation processes of arc plasma include recombination radiation and bremsstrahlung; both recombination radiation and bremsstrahlung are continuous spectrum radiations. Recombination radiation is the radiation emitted when electrons and ions collide and combine with each other, and bremsstrahlung is the radiation emitted when the kinetic energy of electrons changes during the collision between electrons and ions.

[0007] Currently, although some researchers have used the bremsstrahlung process to measure the temperature of arc plasma, they have ignored the recombination radiation received by the acquisition system, which has certain deficiencies. Therefore, considering the specific radiation process of arc plasma, especially considering the recombination radiation process, is of great significance for improving the arc plasma temperature measurement method. Summary of the Invention

[0008] In view of the above deficiencies of the prior art, the present invention proposes a method for measuring the temperature of arc plasma considering recombination radiation. Based on the spectral radiation theory, according to the specific radiation process of arc plasma, using the recombination radiation and bremsstrahlung formulas, the more accurate temperature of arc plasma is finally obtained through the colorimetric temperature measurement method.

[0009] The method for measuring the temperature of arc plasma considering recombination radiation is specifically as follows:

[0010] Step 1: Use a standard radiation source to calibrate the optical channel of the color CCD high-speed camera to obtain the analog-to-digital conversion ratio coefficient K of each optical channel including the exposure time. 10 and K 20 The ratio of

[0011] First, calculate the standard radiation source at the center frequency f 1 and f 2 The corresponding monochromatic radiation brightness I 1 and I 2 ;

[0012]

[0013]

[0014] Where c is the speed of light, h is Planck's constant, k is the Boltzmann constant, and T is the temperature.

[0015] Then, the R (red), G (green), and B (blue) values ​​corresponding to a single pixel in the CCD high-speed camera storage file are used to calculate the analog-to-digital conversion (A / D conversion) proportional coefficient K including the exposure time. 10 and K 20 ratio.

[0016] The calculation formula is:

[0017]

[0018] In the formula, R, G, and B are the R, G, and B three-color values ​​corresponding to a single pixel, which can be obtained from the ".RAW" format file stored in the CCD high-speed camera;

[0019] η 1 is the filter at the center frequency f 1 The transmittance at 2 is the filter at the center frequency f 2 The transmittance at

[0020] {R 1 ,R 2}, {G 1 ,G 2}、{B 1 ,B 2} are the center frequencies f 1 and f 2 The photoelectric response coefficient of the radiation power at R, B, and G color pixels is a known quantity.

[0021] By combining any two equations in the above formula, we can get the A / D conversion ratio coefficient K. 10 and K 20 ratio.

[0022] Step 2: For the arc to be measured, use the calibrated color CCD high-speed camera and cooperate with a double-peak narrowband filter to measure the arc, and obtain the.RAW file of the arc;

[0023] The central frequencies of the double-peak narrowband filter are f 1 and f 2 .

[0024] Step 3: Use the.RAW file of the arc to calculate the relationship between the radiation power I 1 and I 2 received by the camera sensor at the two central frequencies f h1 , I h2 and the R, G, B color values;

[0025] The simultaneous equations are as follows:

[0026]

[0027] where K 1 and K 2 are the A / D conversion proportionality coefficients including the exposure time when taking the arc image, and K 1 / K 2 =K 10 / K 20 .

[0028] Step 4: Use the composite radiation and bremsstrahlung to calculate the radiation power I h1 of the arc to be measured received by the camera sensor and I h2 . After passing through the filter, the camera senses light, and the A / D conversion, a digital quantity DT 1 containing the arc plasma temperature and DT 2 are obtained;

[0029] First, calculate the radiation power I 1 and I 2 received by the camera sensor at the central frequencies f h1 and I h2 respectively;

[0030]

[0031]

[0032] In the formula, Ω is the solid angle subtended by the measured point with respect to the lens; S is the area of the measured point corresponding to the pixel; W is the arc thickness in the observation direction; K g (f) is the spectral characteristic of the photodiode; K f (f) is the spectral characteristic of the filter; f L1 and f H1They are the frequencies when the low-frequency response and the high-frequency response of the filter with a center frequency of f 1 are zero; f L2 and f H2 are the frequencies when the low-frequency response and the high-frequency response of the filter with a center frequency of f 2 are zero; is the radiation power density emitted by plasma bremsstrahlung per unit volume, per unit solid angle, and within a frequency interval of f; is the radiation power density emitted by plasma recombination radiation per unit volume, per unit solid angle, and within a frequency interval of f;

[0033] Then, the digital quantities DT h1 and DT h2 after the light passes through the filter, the camera senses light, and A / D conversion are calculated respectively; 1 and DT 2 ;

[0034] DT 1 = I h1 η 1 R 1 K 1

[0035] DT 2 = I h2 η 2 B 2 K 2

[0036] Step Five: Based on the colorimetric temperature measurement method, the ratio of the digital quantities DT 1 and DT 2 after the light passes through the filter, the camera senses light, and A / D conversion is taken to eliminate the unknown quantities that cannot be directly calculated in the radiation power calculation formula, and the arc plasma temperature is obtained;

[0037] When f 1 and f 2 are respectively selected as a certain frequency in the red region and a certain frequency in the blue region:

[0038] R = DT 1

[0039] B = DT 2

[0040] The calculation formula is:

[0041]

[0042] The frequencies collected through the filter are f H1 and f L1 , f H2 and f L2The optical radiation density within the section can be considered with the filter characteristics and the spectral characteristics of the photosensitive diode being rectangular and having constant values within the measured range. The electron density in the plasma is equal to the ion density. The diameter of the measured point is relatively small compared to the distance to the lens, so the solid angle subtended by the measured point at the lens within the diameter of the measured point can be regarded as a constant. At the same time, the area of the measured point is very small, and the light intensity and the arc thickness in the observation direction within this area can also be regarded as constants.

[0043] Then the calculation formula can be simplified as:

[0044]

[0045] In the formula,

[0046] T e is the temperature of the arc plasma; Z is the atomic number; n is the principal quantum number of the energy level, and its value is related to the central frequency f; E n is the electron energy level; N e is the electron density; is the correction factor caused by quantum mechanical effects;

[0047] Compared with the prior art, the advantages of the present invention are as follows:

[0048] 1. For the method for measuring the temperature of arc plasma considering recombination radiation in the present invention, the acquisition system is easy to build. By using a CCD color camera and a double-peak narrowband filter, non-contact temperature measurement of arc plasma can be more accurately realized.

[0049] 2. For the method for measuring the temperature of arc plasma considering recombination radiation in the present invention, the specific radiation process of arc plasma is considered. According to the relationship between the recombination radiation and bremsstrahlung intensity and temperature of arc plasma, colorimetric temperature measurement of arc plasma is carried out, which is more in line with the actual physical process and provides an important idea for the improvement of arc plasma diagnostic methods. Description of the Drawings

[0050] Figure 1 is the flowchart of the method for measuring the temperature of arc plasma considering recombination radiation in the present invention;

[0051] Figure 2 is the schematic diagram of non-contact temperature measurement of arc plasma using a color CCD camera and a double-peak narrowband filter during the implementation of the present invention. Detailed Embodiment

[0052] To facilitate the understanding and implementation of the present invention by those of ordinary skill in the art, the present invention will be further described in detail and in depth below with reference to the drawings.

[0053] The present invention discloses a method for measuring the temperature of arc plasma considering compound radiation. By using a color CCD high-speed camera in cooperation with a double-peak narrowband filter, the radiation powers at two central frequencies are accurately calculated, and combined with the compound radiation and bremsstrahlung processes of the arc plasma, the temperature of the arc plasma is calculated.

[0054] Arc plasma is a rarefied gas, and its temperature cannot be directly calculated using Planck's blackbody radiation formula. It needs to be calculated by combining the compound radiation and bremsstrahlung processes in the specific radiation process. At present, some researchers use the bremsstrahlung formula to measure the temperature of arc plasma, but they ignore the compound radiation received by the acquisition system, which has certain deficiencies. Based on the spectral radiation theory, the present invention particularly considers the compound radiation and bremsstrahlung processes of arc plasma, and finally obtains a more accurate temperature of arc plasma through the method of colorimetric temperature measurement, providing an important method for measuring the temperature of arc plasma.

[0055] The method for measuring the temperature of arc plasma considering compound radiation is as Figure 1 shown, and the specific steps are as follows:

[0056] Step 1: Calibrate the optical channels of the color CCD high-speed camera using a standard radiation source to obtain the ratio of the analog-to-digital conversion proportionality coefficients K 10 and K 20 including the exposure time;

[0057] First, calculate the monochromatic radiation brightnesses I 1 and I 2 corresponding to the standard radiation source at the central frequencies f 1 and f 2 respectively;

[0058]

[0059]

[0060] In the formula, c is the speed of light, h is Planck's constant, k is Boltzmann's constant, and T is the temperature.

[0061] Then, use the R (red), G (green), and B (blue) color values corresponding to a single pixel in the storage file of the CCD high-speed camera to calculate the ratio of the analog-to-digital conversion (A / D conversion) proportionality coefficients K 10 and K 20 including the exposure time.

[0062] The calculation formula is:

[0063]

[0064] In the formula, R, G, and B are the R, G, and B three-color values ​​corresponding to a single pixel, which can be obtained from the ".RAW" format file stored in the CCD high-speed camera;

[0065] η 1 is the filter at the center frequency f 1 The transmittance at 2 is the filter at the center frequency f 2 The transmittance at

[0066] {R 1 ,R 2}, {G 1 ,G 2}、{B 1 ,B 2} are the center frequencies f 1 and f 2 The photoelectric response coefficient of the radiation power at R, B, and G color pixels is a known quantity.

[0067] By combining any two equations in the above formula, we can get the A / D conversion ratio coefficient K. 10 and K 20 ratio.

[0068] Step 2: For the arc to be measured, use a calibrated color CCD high-speed camera and a double-peak narrow-band filter to measure the arc and obtain a .RAW file of the arc;

[0069] The center frequencies of the double-peak narrowband filters are f 1 and f 2 According to the three-color response curves of the CCD high-speed camera R (red), G (green), and B (blue), try to choose the frequency where the overlapping area of ​​the photosensitive curve is smaller as the center frequency.

[0070] Step 3: Use the .RAW file of the arc to calculate the camera sensor at two center frequencies f 1 and f 2 The received radiation power I h1 ,I h2 Relationship with the three color values ​​of R, G, and B;

[0071] The calculation formula of the three color values ​​of R (red), G (green), and B (blue) corresponding to the pixels in the CCD high-speed camera storage file is as follows: 1 ,I 2 Replace with the radiation power I to be solved h1 with I h2 , using the known R, G, B tristimulus values, and the filter at the center frequency f 1 and f 2 The transmittance η at1 , η 2 , center frequency f 1 and f 2 The photoelectric response coefficient of the radiation power at the R, B, and G three-color pixels {R 1 ,R 2}, {G 1 ,G 2}、{B 1 ,B 2} and the analog-to-digital conversion proportionality factor K including the exposure time 1 , K 2 By combining the equations, we can get I h1 ,I h2 The relationship with the three color values ​​of R, G, and B.

[0072] The simultaneous equations are as follows:

[0073]

[0074] Among them, K 1 and K 2 K is the A / D conversion ratio factor including exposure time when taking arc images. 1 / K 2 =K 10 / K 20 The influence caused by the different camera aperture size and exposure time when taking arc images and calibrating the camera optical channel using a standard radiation source can be ruled out.

[0075] The double peak narrow band filter selects the frequency where the overlapping area of ​​the sensitivity curve is smaller as the center frequency f 1 and f 2 , the photoelectric response coefficients of the radiation power at each center frequency on the R, B, and G color pixels vary greatly, for example, f 1 and f 2 Select a frequency in the red area and a frequency in the blue area respectively. When calculating the R value, the camera is at the center frequency f 2 Photoelectric response coefficient R under 2 can be ignored, and the equation can be simplified as follows:

[0076]

[0077] Step 4: Use the radiation power formula of arc plasma recombination radiation and bremsstrahlung to calculate the radiation power I of the arc to be measured received by the camera's photodiode. h1 with I h2 After the filter transmits light, the camera senses light and A / D conversion, the digital value DT containing the arc plasma temperature is obtained. 1 With DT 2 ;

[0078] The radiation power density formula is from "High Temperature Plasma Diagnostic Techniques" and is derived based on the particle motion in the actual physical process. The theoretical formula contains unknown quantities that cannot be directly measured. Through the theoretical formula, the radiation densities corresponding to two central frequencies can be listed respectively (including complex unknown quantities and the ultimately required temperature T e ). According to the radiation density and digital quantity conversion formula, DT 1 and DT 2 are obtained respectively. Using division (at this time, both the numerator and denominator contain complex unknown quantities and temperature T e ), the complex unknown quantities in the numerator and denominator can be eliminated. At this time becomes an expression that only contains temperature T e and other known quantities. When f 1 and f 2 select a certain frequency in the red region and a certain frequency in the blue region respectively, according to the digital quantity ratio = the ratio of R and B in the camera's RAW file , the only unknown quantity temperature T e in the expression is solved.

[0079] The radiation power received by the photodiode and the digital quantities DT 1 and DT 2 need to consider the radiation power in the arc plasma recombination radiation process and the bremsstrahlung radiation process, and are calculated in combination with the photoelectric conversion coefficient of the acquisition system and the A / D conversion technology. Specifically:

[0080] For a plasma with an electron temperature of T e , the radiation power density emitted in the bremsstrahlung radiation process per unit volume, within a frequency interval of f is:

[0081]

[0082] In the formula, N e and N i are the electron and ion densities respectively; is the correction factor caused by quantum mechanical effects, the Gaunt factor; Z is the atomic number; k is the Boltzmann constant; h is the Planck constant.

[0083] The radiation power density of the plasma per unit volume, per unit solid angle, within a frequency interval of f is:

[0084]

[0085] For a plasma with an electron temperature of T eThe radiation power density emitted by the plasma during the recombination radiation process per unit volume within the frequency interval of f is:

[0086]

[0087] where n is the principal quantum number of the energy level, and its value is related to the frequency; E n is the electron energy level.

[0088] The radiation power density of the plasma per unit volume, per unit solid angle, within the frequency interval of f is:

[0089]

[0090] Using the radiation power in the recombination radiation and bremsstrahlung processes of the arc plasma, calculate the radiation power I 1 and I 2 received by the camera sensor at the central frequencies f h1 and I h2 ;

[0091]

[0092]

[0093] where K gf = K g ·K f .

[0094] where Ω is the solid angle subtended by the measured point with respect to the lens; S is the area of the measured point corresponding to the pixel; W is the arc thickness in the observation direction; K g (f) is the spectral characteristic of the photodiode; K f (f) is the spectral characteristic of the filter; f L1 and f H1 are respectively the frequencies at which the low-frequency response and high-frequency response of the filter with a central frequency of f 1 are zero; f L2 and f H2 are respectively the frequencies at which the low-frequency response and high-frequency response of the filter with a central frequency of f 2 are zero;

[0095] and are the power densities. When calculating, integrate with respect to f, which is essentially summing up continuous phenomena. The upper and lower limits of the integral in the numerator are f H1 and f L1 , representing that the f in the integral ranges from f L1 to f H1 including f 1 .

[0096] Similarly, the upper and lower limits of the denominator integral are f H2 and f L2 , representing that the integration of f ranges from f L2 to f H2 including f 2 .

[0097] The light radiation density in the frequency range of f H1 and f L1 , f H2 and f L2 is collected through the filter. It can be considered that the characteristics of the filter and the spectral characteristics of the photodiode are rectangular, and their values are constant within the measured range. The electron density in the plasma is equal to the ion density. The diameter of the measured point is very small relative to the distance to the lens, so the solid angle subtended by the measured point diameter at the lens can be regarded as a constant. At the same time, the area of the measured point is very small, and the light intensity and the arc thickness in the observation direction within this area can also be regarded as constants.

[0098] Then, the radiation power I h1 received by the photodiode and I h2 are used to calculate the digital quantities DT 1 and DT 2 after passing through the filter, being sensed by the camera, and A / D conversion respectively;

[0099] DT 1 = I h1 η 1 R 1 K 1

[0100] DT 2 = I h2 η 2 B 2 K 2

[0101] Step 5: Based on the colorimetric temperature measurement method, take the ratio of the digital quantities DT 1 and DT 2 after passing through the filter, being sensed by the camera, and A / D conversion to eliminate the unknown quantities that cannot be directly calculated in the radiation power calculation formula, and obtain the temperature of the arc plasma;

[0102] First, rewrite the digital quantities DT 1 and DT 2 as:

[0103]

[0104]

[0105] In the formula,

[0106] T e is the arc plasma temperature; Z is the atomic number; n is the principal quantum number of the energy level, and its value is related to the central frequency f; E n is the electron energy level; N e is the electron density; is the correction factor caused by quantum mechanical effects, the Gaunt factor;

[0107] When f 1 and f 2 are respectively selected as a certain frequency in the red region and a certain frequency in the blue region:

[0108] R = DT 1

[0109] B = DT 2

[0110] Based on the colorimetric temperature measurement method to calculate the arc plasma temperature, the calculation formula is:

[0111]

[0112] In the formula,

[0113] Example:

[0114] Using a color CCD camera and a double-peak narrow-band filter as shown in Figure 2 to build an optical acquisition system, calibrate the optical system through a temperature standard radiation source, and take pictures of the arc plasma; the specific process is as follows: First, calibrate the optical system using a temperature standard radiation source, and use a color CCD high-speed camera in cooperation with double-peak narrow-band filters with central frequencies of f 1 and f 2 to measure the arc image; then, the radiation powers I h1 , I h2 at two central frequencies and the relationship between the R, G, and B color values are obtained by the CCD high-speed camera storing files; then, according to the radiation powers in the processes of arc plasma recombination radiation and bremsstrahlung radiation, calculate the radiation power received by the photodiode and the digital quantities DT 1 , DT 2 ; finally, to avoid the situation where the absolute light intensity of the arc plasma cannot be solved due to multiple unknown parameters in the formula, through the relative light intensity of the arc plasma, the arc plasma temperature can be obtained, that is, calculate the arc plasma temperature based on the colorimetric temperature measurement method.

Claims

1. A method for measuring the temperature of arc plasma considering composite radiation, characterized in that, the specific steps are as follows: First, calibrate the optical channel of the color CCD high-speed camera using a standard radiation source; Then, for the arc to be measured, use the calibrated color CCD high-speed camera, in cooperation with a double-peak narrowband filter, to measure the arc and obtain the.RAW file of the arc; and further calculate the relationship between the radiation power I 1 and f 2 received by the camera sensor at two center frequencies f h1 、I h2 and the RGB three-color values; Next, using the combined radiation and bremsstrahlung, calculate the radiation power I of the arc to be measured received by the camera sensor h1 and I h2 , and after passing through the filter, the camera senses light and undergoes A / D conversion, a digital quantity DT containing the temperature of the arc plasma is obtained 1 and DT 2 ; Finally, based on the colorimetric temperature measurement method, the ratio of DT 1 to DT 2 is taken to eliminate the unknown quantity in the radiation power formula, and the temperature of the arc plasma is obtained.

2. A method for measuring the temperature of arc plasma considering composite radiation according to claim 1, characterized in that, The calibration refers to calculating the analog-to-digital conversion proportionality coefficient K including the exposure time for each optical channel 10 and K 20 for their ratio; the process is as follows: First, calculate the monochromatic radiance I 1 corresponding to the standard radiation source at the center frequencies f 2 and f 1 respectively; 2 ​ where c is the speed of light, h is Planck's constant, k is Boltzmann's constant, and T is the temperature; Then, the red, green, and blue color values corresponding to a single pixel in the file stored by the CCD high-speed camera are utilized to calculate the analog-to-digital conversion proportionality coefficient K including the exposure time 10 and K 20 for their ratio; The calculation formula is: where R, G, and B are the R, G, and B color values corresponding to a single pixel, obtained from the ".RAW" format file stored by the CCD high-speed camera; η 1 is the transmittance of the filter at the center frequency f 1 ; η 2 is the transmittance of the filter at the center frequency f 2 ; {R 1 , R 2}, {G 1 , G 2}, {B 1 , B 2} are the photoelectric response coefficients of the radiation energy at the center frequencies f 1 and f 2 on the R, B, and G color pixels, and are known quantities; By combining any two equations in the above formula, we can get the A / D conversion ratio coefficient K. 10 and K 20 ratio.

3. A method for measuring the temperature of arc plasma considering composite radiation according to claim 1, characterized in that, The calculated radiation power I h1 、I h2 The simultaneous equations for the relationship with the RGB color values are as follows: K 1 and K 2 is the analog-to-digital conversion scale coefficient of the exposure time for each optical channel during camera calibration for capturing the arc image, K 1 / K 2 = K 10 / K 20 .

4. A method for measuring the temperature of arc plasma considering composite radiation according to claim 1, characterized in that, The calculated center frequency f 1 and f 2 of the radiation power I received by the camera sensor below h1 and I h2 , the formula is: Wherein, Ω is the solid angle subtended by the measured point with respect to the lens; S is the area of the measured point corresponding to the pixel; W is the arc thickness in the observation direction; K g (f) is the spectral characteristic of the photosensitive diode; K f (f) is the spectral characteristic of the filter; f L1 and f H1 are respectively the frequencies at which the low-frequency response and the high-frequency response of the filter with a center frequency of f 1 are zero; f L2 and f H2 are respectively the frequencies at which the low-frequency response and the high-frequency response of the filter with a center frequency of f 2 are zero; is the radiation power density emitted by plasma bremsstrahlung per unit volume, per unit solid angle, and within a frequency interval of f; is the radiation power density emitted by plasma recombination radiation per unit volume, per unit solid angle, and within a frequency interval of f; Then, the radiation power I h1 and I h2 are respectively used to calculate the digital quantity DT 1 after the light passes through the filter, the camera senses the light, and the A / D conversion, and 2 ; DT 1 = I h1 η 1 R 1 K 1 DT 2 = I h2 η 2 B 2 K 2 .

5. A method for measuring the temperature of arc plasma considering composite radiation according to claim 1, characterized in that, The colorimetric temperature measurement method for the digital quantity DT 1 and DT 2 to make a ratio, and the process of obtaining the temperature of the arc plasma is as follows: First, when f 1 and f 2 select a certain frequency in the red area and a certain frequency in the blue area respectively: R = DT 1 B = DT 2 calculate the temperature of the arc plasma based on the colorimetric temperature measurement method, and the calculation formula is: Wherein, T e is the arc plasma temperature; Z is the atomic number; n is the principal quantum number of the energy level, and its value is related to the central frequency f; E n is the electron energy level; N e is the electron density; is the correction factor caused by quantum mechanical effects.

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