RU2439597C1 - Apparatus for measuring characteristics of radiation receivers - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: apparatus has a collimator with a test object in its focal plane, the output of which is connected to the input of the radiation receiver, a video viewing device, an oscilloscope and a synchronisation and control panel. The oscilloscope is a double-beam oscilloscope. The output of the radiation receiver is connected to the input of the synchronisation and control panel and the input of the first channel of the oscilloscope. The first output of the synchronisation and control panel is connected to the input of the video viewing device. The second output of the synchronisation and control panel is connected to the input of the second channel of the oscilloscope.

EFFECT: high reliability of measurements, high information content and accuracy of controlling and cutting time for measuring parameters of radiation receivers.

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Description

The invention relates to instrumentation and is intended for measuring the parameters of television-type radiation receivers.

A well-known installation for determining the characteristics of radiation receivers (thermal), described in the article "Installation for measuring the characteristics of thermal imaging devices" in the journal "Questions of defense technology" 1986, ser. 10, issue 6, authors V.A. Lening, M.I. .Gudnyak, V.O.Shigin and others. The installation consists of a collimator that generates signals of a test object and background with a given temperature difference, a tested radiation receiver, an infrared radiometer, a video viewing device - APU (TV), a microphotometer, and a temperature difference controller between test volume project and background, recorder and photometer control panel. A disk with worlds is placed in the focal plane of the collimator, behind which there is a background emitter. The installation is used to determine the characteristics:

- the minimum allowable temperature difference ΔT _Mr ;

- the minimum detectable temperature difference ΔT _mo ;

- temperature-frequency characteristic;

- gradation characteristic.

In this setup, additional errors are introduced by the APU and the microphotometer due to the noise and scattered light that occur both on the APU screen and in the measuring circuit of the microphotometer. In addition, the measurement errors still depend on the level of nonlinear distortion of the APU raster and the subjective error of the operator when combining the microphotometer slit with the world lines on the APU screen during the measurement of the minimum resolved temperature difference and the minimum detectable temperature difference.

Closest to the proposed technical solution is the installation for measuring the resolution and dynamic range of the radiation receiver (camera module), described by V. M. Smelkov in the article "Methodology for assessing the dynamic range of a television system" in the journal "Special equipment" 2007, No. 4. The installation consists of a signal generator of a test object, which includes a light cabinet, an illumination measurement unit, a test table, and a pipe (all this together is an analog of the collimator); the tested radiation receiver (camera module), a video monitor (video viewing device - APU), a weighing filter, an oscilloscope and a computer. The test object consists of two parts in A4 format, each of these parts consists of ten groups of vertical lines with a constant step along the horizontal direction. Each group of vertical lines occupies the entire width of the A4 format and differs from neighboring groups in the step size of vertical lines.

The optical signal of the test object from the output of the collimator is fed to the input of the camera module, from the output of which the video signal is fed to the input of the APU, and then through the weighting filter is fed to the input of the oscilloscope and computer. To assess the resolution, the concept of modulation depth (modulation coefficient - m _x ) of the video signal obtained on the oscilloscope screen with highlighting the line is used. The value of the modulation coefficient - m _x is determined by the formula

Where

A - the highest point of the video signal formed from the bands of the worlds;

In - the lowest point of the video signal formed from the bands of the worlds.

This assessment is considered accepted if the modulation coefficient m _{x of the} video signal corresponding to a specific group of vertical lines of the test object is at least 5%.

The dynamic range D is defined as the ratio of the limiting illuminances of objects within a single observed scene, and it is expressed in decibels

Where

E _max - maximum illumination of the test table, which ensures the maximum resolution of the television module;

E _min is the minimum illumination of the test table, taken according to two criteria, namely, the threshold signal-to-noise ratio at the output of the television module, which should be at least 10, and the threshold resolution, the value of which is taken 3 times less than the resolution, obtained by determining E _max .

Images observed during measurements of the dynamic range of the camera module were recorded on a computer.

The advantages of this technical solution include the lack of subjective error in measuring resolution and dynamic range. This is explained by the fact that direct participation of the eye-brain link is excluded in the system of evaluating the measured parameters, and photometric (light meter) and electric (oscilloscope) meters are used directly for evaluation.

Additional errors of this setting depend on the accuracy of inscribing the test table into the raster of the television module, on the correct identification of the video signal measured on the oscilloscope screen with the corresponding group of vertical lines of the test table on the video monitor screen, which takes additional time. However, it should be noted the small functionality of the considered circuit in terms of determining other parameters of radiation receivers such as vertical resolution, gradation characteristic, etc.

The challenge posed to the proposed technical solution is to increase the operational characteristics of the installation.

The technical result is an increase in the reliability of measurements, an increase in the information content and accuracy of control, and a reduction in time for measuring parameters of radiation receivers.

This is achieved by the fact that the installation for measuring the characteristics of radiation receivers, containing a collimator with a test object in its focal plane, the output of which is connected to the input of the radiation receiver, a video viewing device, and an oscilloscope, in contrast to the known one, contains a synchronization and control panel. The oscilloscope is double-beam. The output of the radiation receiver is connected to the input of the synchronization and control panel and to the input of the first channel of the oscilloscope. The first output of the synchronization and control panel is connected to the input of the video viewing device. The second output of the synchronization and control panel is connected to the input of the second channel of the oscilloscope.

The technical solution is illustrated by drawings, where in Fig.1 shows a block diagram of the installation, and Fig.2 shows a test object.

Installation for measuring the characteristics of radiation receivers (figure 1) consists of a collimator 1, in the focal plane of which is a test object. The output of the collimator is connected to the input of the radiation receiver 2. Depending on the type of radiation receiver 2, which is determined by its spectral operating range, and this can be, for example, a thermal imaging or television module, the type of collimator 1 is also determined. The output of the radiation receiver 2 is connected to the input of the first channel a two-beam oscilloscope 3 and with the input of the synchronization and control panel 4. The first output of the synchronization and control 4 is connected to the input of the video viewing device (APU) 5, and the second output is connected to the input of the second channel of the two-beam oscillograph 3.

All devices included in the installation (Fig. 1), except for the synchronization and control panel (UCS) 4, are typical and are used for their intended purpose. UCS 4, introduced into the installation block diagram, allows generating a backlight pulse for the line selected by the operator on the APU screen 5, inputting it into the output video signal of the radiation receiver, and simultaneously synchronizing the two-beam oscilloscope 3 with the same backlight pulse.

Figure 2 shows the test object in the form of worlds, consisting of several groups of vertical and horizontal stripes, with different spacing of these bands between the groups, and within each group the stripe pitch is constant. The magnitude of the stripe step can be determined both by the resolution of the radiation detector being tested, and by the boundary frequency of the passband of its amplification path.

This installation works as follows. The collimator 1 generates an optical signal of the test object, which is fed to the input of the radiation detector 2. The radiation receiver 2 from the optical signal generates a video signal of the image of the test object, which is simultaneously fed to the input of UCS 4 and the input of the first channel of the oscilloscope 3. To synchronize the oscilloscope 3 to the input its second channel from the output of UCS4, a backlight pulse is received for the line highlighted by the operator on the screen of the APU 5. From the first output of the UCS 4, the video signal is input to the APU 5. This video signal is different from the video signal at the output of the receiver ka radiation 2 only in that it entered the selected row pulse illumination. The selection of the highlighted line is carried out by the operator by switching three dial switches located on the front panel of the UCS 4.

To illustrate the application of the measuring installation (figure 1) below, methods of measuring a number of parameters of radiation receivers are discussed.

The resolution measurement along the lines of the radiation receiver is as follows. On the collimator 1, set the set temperature difference (illumination), select on the APU 5 screen a line passing through the image of the worlds with vertical lines (Fig. 2), and receive on the oscilloscope 3 screen, for example, "Tektronix" video signals of the selected line one below the other and pulse backlight. In the "Cursor" mode measure the maximum - A and minimum - B of the video signal value of the selected line belonging to a specific group of vertical lines of the test object. Using formula (1), determine the modulation coefficient m _{x of the} video signal.

This assessment of resolution for a given temperature contrast (illumination) is considered acceptable if the modulation coefficient m _{x of the} video signal corresponding to a particular group of vertical lines of the test object is at least 5%.

To measure the resolution in the direction perpendicular to the lines of the raster (along the frame), you must select a line in front of the top line of the group of horizontal stripes, which determines the resolution (figure 2). Given the relative position of the waveforms of the selected line pulse and the video signals from the selected group of horizontal lines of the test object, determine the group of lines along which the video signals of these lines have one period of change. In one of these periods, measure the video signal in the line with the maximum value - A and the video signal in the line with the minimum value - B and using formula (1) determine the modulation coefficient of the video signal along the frame - m _y for the selected group of horizontal stripes of the test object (Fig. 2 ) An assessment of the resolution of the radiation receiver along the frame is considered acceptable if the modulation coefficient m of _the video signal belonging to a specific group of horizontal lines of the test object for a given temperature contrast is not less than 5%. To measure the dynamic range of the radiation receiver, set the collimator 1 to the minimum temperature difference (illumination) at which the image of the worlds of the test object is visible on the screen of the APU 5 (figure 2), and select the line passing through the groups of vertical lines. To increase the temperature contrast (illumination) to a value at which, according to the criterion m _x greater than or equal to 5%, a group of vertical lines with a maximum step is allowed. This value of temperature contrast (illumination) is designated ΔT _min (E _min ). In the process of a further increase in ΔT (E), taking into account the same criterion, ΔT _min (E _min ) should be determined. For all other groups of vertical lines of the test object, as well as the maximum value of the temperature contrast ΔT _max (E _max ) for each group of vertical lines of the test object, at which the criterion m _x is satisfied. The resulting family of ΔT _min (E _min ) and ΔT _max (E _max ) values allows us to determine, according to formula (2), the dynamic range of the radiation receiver both for a specific resolution value and for the resolution range of the device under test, as well as construct for a thermal imaging receiver radiation temperature-frequency characteristic.

The measurement of the amplitude-frequency characteristic (AFC) of the radiation receiver is measured at a constant temperature difference ΔT = const (illumination E = const), which is equal to the middle of the dynamic range obtained by determining the maximum resolution for the tested radiation receiver. To measure the frequency response, select the line passing through the image of groups of vertical lines (figure 2). On the oscilloscope 3 screen, receive video signals of the highlighted line and the backlight pulse of this line, which should be located one below the other. In the "Cursor" mode, measure the amplitude U and frequency F. The frequency response is plotted from the measured values of U and F, which allows you to determine the end-to-end bandwidth of the channel of the radiation detector under test.

To measure the gradation characteristics of the radiation receiver, set the temperature difference ΔТ = 0K on the collimator, measure the magnitude of the video signal of the selected line (background level) on the left border of the image of the rectangle of the test object (Fig. 2). After each increase in the contrast temperature difference ΔT by 1K, measure the video signal of the highlighted line on the oscilloscope screen. Using the data obtained, construct the gradation characteristic of the thermal imaging device - U = f (ΔТ). To measure the gradation characteristics of a sensitive radiation receiver in the visible spectral range, you need to get a clear image, for example, television test table 0249, select a line passing through a horizontal gradation wedge, and measure the video signal of each gradation of brightness on the oscillogram of the gradation wedge. Build the gradation characteristic of the tested radiation receiver.

Thus, the introduction of PSK 4 into the measuring circuit allows us to quickly and unambiguously solve the problem of identifying the video signal observed on the screen of the oscilloscope 3 with the video signal of the highlighted line on the APU 5, which significantly reduces the time it takes to measure each parameter of thermal imaging (television) devices and increases the accuracy and reliability obtained results and at the same time allows to increase the number of measured parameters of television-type radiation receivers, to exclude subjective error in measurements due to the fact that In the system of evaluating these parameters, the direct participation of the operator’s eye-brain link is excluded; photometric and electrical meters are used directly to evaluate the parameters.

Claims (1)

Installation for measuring the characteristics of radiation receivers, containing a collimator with a test object in its focal plane, the output of which is connected to the input of the radiation receiver, a video inspection device and an oscilloscope, characterized in that a synchronization and control panel is introduced into the installation, and the oscilloscope is double-beam, while the output of the radiation receiver is connected to the input of the synchronization and control panel and to the input of the first channel of the oscilloscope, the first output of the synchronization and control panel is connected to the input of the video viewing device and the second output of the synchronization and control panel is connected to the input of the second channel of the oscilloscope.

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