RU2032919C1 - Method of measurement of low altitudes and device for its realization - Google Patents

Abstract

FIELD: radiation instrumentation. SUBSTANCE: in compliance with method of measurement of low altitudes surface of reflector is irradiated with pulses with fixed repetition frequency and duration τ, reflected signals are registered, strobes of equal duration are formed and their position on time axis is determined. Information comb is formed from three strobes of same type adjacent to each other. Direction of movement of maximum of reflected signal is observed by position on time axis and comb is moved to one or other side over time axis by time equal to strobe duration. Altitude range is divided into virtual strobe. Number of pulses per accumulation period in m-th and m+1 strobe of comb is calculated, is multiplied by weight coefficients and value of altitude is computed. Device for realization of method has X-ray transmitter 1, detector 2, strobe former 3, two delay lines 4,5, three coincidence circuits 6,7,8, three counters 9,10,11 and computer 12. EFFECT: enhanced reliability of measurement. 2 cl, 6 dwg

Description

 The invention relates to radiation instrumentation, namely to controlled pulsed x-ray devices.

Known methods for measuring small heights and x-ray altimeters of small heights (WWW), developed in the USA and described in [1]
The height measurement in them is based on the active location of the reflection surface by the generator and the reception of the reflected pulse by a scintillation detector. Altimeters contain a transmitter-generator of x-ray pulses with a triode tube type, a plastic scintillator receiver with a fast PMT, and a device for controlling the duration and pulse repetition rate.

 Their disadvantages are: a small range of measured heights, the requirement of mandatory stabilization of the receive-transmit path for primary radiation, and also the dependence on the type of reflective surface.

 The closest in technical essence to the proposed technical solutions is a method for measuring low heights and a device for its implementation [2] A method for measuring low heights is based on the allocation of the maximum backscattered quanta recorded by the detector. To do this, the reflector surface is irradiated with X-ray pulses of 10 ns duration, the reflected quanta are recorded, amplify them, and strobe pulses of 10 ns duration shifted by 15 ns relative to each other are formed from probing radiation pulses. Next, determine the number of reflected x-ray quanta that arrived during the action of the strobe pulse, and equalize the statistics of quanta scattered by air at different distances from the detector, adjusting the level of background pulses.

 At the same time, the position of the pair of strobe pulses on the time axis and the maximum of the X-ray pulse signal from the reflector are determined. When this signal decreases, the gates stop and change the geometry, i.e. distance to reflective surface. Next, the measurement process is repeated until the maximum reflected x-ray pulse in the new geometry. Thus, in the known method, a narrow gate synchronized by the frequency of operation of the x-ray generator, sequentially "look through" the localized volume of air and the surface of the reflector, identifying the quanta scattered by the reflector and the air.

 This method is implemented in the device described in / 2 / and which is closest to the proposed technical solution. The device contains an X-ray transmitter RP consisting of a power source, a modulator, and an X-ray tube, a detector (a DB detection unit) connected to an amplifier, the first inputs of keys K1 and K2 are connected to its output. The device also includes a gate generator, the outputs of which are connected to the second key inputs: directly to the key K1, and to the key K2 through the delay line, as a result of which the strobe pulses are shifted relative to each other by 15 ns. Thus, the signal from the gate driver controls both keys, the outputs of which are connected to the integrators one and two, respectively. The outputs of the first integrator through a parallel circuit from the discriminator of the upper level and the discriminator of the lower level, is connected to the level controller, the output of which is connected to the modulator. The output of the second integrator is connected to the 1st input of the comparison circuit and through a threshold former with the second input of the comparison circuit.

 The output of the comparison circuit is connected to a sawtooth generator connected to the first input of the adjustable delay line, the second input of which is connected to the modulator, and the output to the gate former.

The disadvantages of the known method and device are:
significant probability of missing the surface of the reflector;
the probability of failure to follow the surface of the reflector, leading to the need for repeated "viewing" of the entire measurement range;
low accuracy of height measurement due to a systematic error associated with the shape of the reflected signal, since the peak maximum of this signal is extracted and the “reflector” surface is “viewed” using only one strobe, in which the center of gravity of the peak of the reflected signal does not correspond to the height value, which connected to the front of this peak of the reflected signal.

 The aim of the proposed technical solutions is to eliminate these drawbacks using a new dynamic gating scheme that eliminates information skipping and improves the accuracy of height measurement. In addition, the proposed solutions make it possible to obtain additional information about the instantaneous value of the vertical speed (rate of change of height).

Figure 1 presents the structural electrical diagram of a device that implements the proposed method; figure 2 time spectra of reflected radiation for ten different heights in the region of low heights; on figa schematically shows three strobe information comb with a recorded number of reflected pulses N _II , N _III at the upper boundary of the range of measured heights N1; figure 3, b histogram of the account N _I , N _II , N _III , figure 3, in the histogram of the account taking into account the weight coefficients K _I , K _II , K _III ; in Fig. 4, the time spectra of reflected radiation for different heights, three gates of the information comb and the ratio of the count in the gates, the shift of the information comb when moving down 4 a, b, c and up 4 g, d; in Fig.5 calibration curve "g _m " and its angle лона in Fig.6 time diagrams explaining the operation of the device.

 The device (Fig. 1) contains an X-ray transmitter 1, a detection unit 2, a gate driver 3, a controlled delay line 4, a multi-tap delay line 5, three matching schemes 6, 7, 8, three counters 9, 10, 11 and a calculator 12.

The proposed method for measuring small heights is that using the x-ray transmitter, the reflector surface is irradiated with probe pulses with a fixed repetition rate and duration τ The x-ray quanta reflected by the environment (air) and the reflector surface are recorded by a scintillation detection unit. The time spectrum of these reflected quanta at different heights is presented in figure 2. Gates of the same duration are formed and their position on the time axis is determined. Three gates I, II, III adjacent to each other (see figure 3), rigidly attached to the moment of emission of the probe pulse and carrying information about the height, are combined into an information comb. The position of the information comb on the time axis monitors the direction of movement relative to the surface of the reflector and discretely shifts it in one direction or another along the axis, for a time equal to the duration of one strobe τ _p
In each of the three gates, the number of reflected quanta is recorded: N _I , N _II , N _III (see Fig. 3, a).

At heights exceeding the upper limit of height measurement, N> Nmax, where there is no useful signal and only quanta reflected from air are recorded, the relation
N _I > N _II > N _III (Fig. 3, b) i.e. the maximum number of pulses accumulates in the second gate. To give stability to the measurement system, the values of N _I , N _II and N _{III are} multiplied by a fixed weight coefficient K _I , K _II , K _III . The coefficients are selected so that on the upper boundary of the range of height measurement (Fig. 3, a) with a probability of not lower than the given one, the relation
K _II N _II > K _I N _I or N _III '> N _I '
K _II N _II > K _III N _III or N _II '> N _III ', where N _I 'K _I ˙N _I ; N _II 'K _II ˙N _II ˙N _II I' K _III ˙N _III (see Fig. 3, c), obviously, K _II > K _I and K _II > K _III
Thus, at heights beyond the upper limit of the measurement range, the reduced peak peak of the reflected signal is in the second gate.

In the case of movement to the reflector surface (down), the peak peak of the reflected signal is shifted to the region of the 1st gate (Fig. 4). After the center of gravity of the peak maximum crosses the boundary of the second and first gates, the ratio
N _II '<N _I '
This ratio serves as a signal along which the information comb is shifted towards lower heights by a time equal to the duration of one strobe of the information comb τ _pp. Therefore, the third gate as it were “disappears”, the second becomes III, the first becomes II and the new 1st gate appears again (Fig. 4, a, b). In this case, the ratios N _II '> N _I ' and N _II '> N _III ' are satisfied again. With further downward movement, the peak peak of the reflected signal will move into the gates of the information comb with lower numbers and then move the comb again for a time equal to the duration of one strobe toward lower heights (Fig. 4c).

If it is necessary to move upward, the peak peak of the reflected signal from the region of the second gate will be shifted to the region of the third gate. In this case, after the center of gravity passes the maximum peak of the boundary of the second and third gates, the account ratio changes and the ratio N _II '<N _III ' is established. According to this signal, the comb is shifted to a region of high altitudes, then the 1st gate will “disappear”, the 2nd gate will become the 1st, and the 3rd gate will become the 2nd, a new third gate will appear again, and then the ratio N _II '< N _III 'will become N _I '<N _II ', a N _II '> N _III '(Fig. 4, d, d).

 From the foregoing, it is clear that for any direction of movement (up or down), the maximum peak of the reflected signal will always be in the second (central) strobe of the information comb, which is the carrier of information about the height. The numerical value of the height is determined by the temporary position of the second gate of the information comb relative to the sync pulse of the x-ray transmitter. To do this, the entire range of heights (from 0 to 30-50 m) is divided into "virtual" gates from 1 to K numbers. Any position of the information comb gates on the “virtual” gates scale has a specific number: from 1 at the lower end of the range to “K” at the top, i.e. 1,2,3. (M-1), m, (m + 1). (K-2), (K-1) K.

 The initial position of the gates of the information comb has the maximum serial numbers (K-2) (K-1) K (figure 2, a).

где С скорость света.When the data comb is shifted, the sequence numbers on the virtual strobe scale are reduced. On the scale of virtual strobes, three constantly functioning strobes carrying height information, i.e. information comb with the maximum peak of the reflected signal in the second gate and notice the number of this gate on the scale of the viral gates, for example m. The strobe with this number is separated from the moment of radiation of the probe pulse by the time (m-1) τ _p which corresponds to the height:
H

where C is the speed of light.

+

tgθ где Θ угол наклона калибровочной кривой q_m;
q_m калибровочная кривая
q_m=

q_m=

(фиг.5)
Калибровочная кривая в пределах длительности одного строба имеет линейную зависимость. Кривую снимают экспериментально. При этом целесообразно середину m-го настроечного строба размещать под границей m-го и m+1-го "виртуальных" стробов.For a more accurate determination of the height, consider the number of pulses accumulated per accumulation cycle in the m-th gate N _m and in the adjacent enclosing strobe m + 1-N _{m + 1} , multiply them by correction factors K _m , K _{m + 1} and get N _m 'and N _{m + 1} '. The value of the height H 'is determined by the formula H' H˙ q _m tgΘ
H ′

+

tgθ where Θ angle of inclination of the calibration curve q _m ;
q _m calibration curve
q _m =

q _m =

(figure 5)
The calibration curve within the duration of one gate has a linear relationship. The curve is removed experimentally. In this case, it is advisable to place the middle of the mth tuning gate under the boundary of the mth and m + 1th “virtual” gates.

по формуле
V

где H(t_o) и H(t_o + τ_нак ) соседние значения измеренной высоты, отстоящие друг от друга по времени на такт накопления τ_нак
Устройство работает следующим образом.Using the proposed method, the instantaneous value of the vertical speed (rate of change of height) VV is also measured

according to the formula
V

where H (t _o ) and H (t _o + τ _nak ) are adjacent values of the measured height, spaced from each other in time by the accumulation cycle τ _nk
The device operates as follows.

В предлагаемом устройстве малых высот модулятор передатчика 1 обеспечивает его работу в импульсном режиме с частотой следования зондирующих импульсов 1 МГц и длительностью не более 10 нс на половине амплитуды интенсивности, при этом квантовый выход РП составляет 10¹²-10¹³ квантов в секунду, их средняя энергия 60 кэВ, максимальная до 100-120 кэВ. Диаграмма направленности передатчика 2Ψ 80^о.X-ray radio transmitter 1 irradiates with nanosecond probe pulses the reflection surface with a given frequency (T probe) (Fig.6, a). Quantums reflected from the surface and surrounding air layers are recorded in block 2 (Fig. 6, b). The sync pulse of the transmitter 1, rigidly attached to the moment of emission of the x-ray pulse, triggers the gate driver 3 (Fig. gates of the same duration and rigidly tied to the moment of emission of the transmitter clock (Fig.6, d, e, e). Gates enter the first inputs of coincidence circuits 6, 7, 8, the second inputs of which receive pulses from block 2. In coincidence circuits 6, 7, 8, temporary selection of pulses takes place, which are caused by the detected x-ray reflected quanta. Counters 9, 10, 11 connected to the outputs of coincidence circuits 6, 7, 8 count the pulses recorded in the gates. The computer 12 controls the operation of the device: polls and clears the counters 9, 10, 11, opens their inputs to the accumulation cycle, and processes the accumulated information. Depending on the result, the calculator controls the delay line LZ, 4, which shifts the information comb of the gates relative to the sync pulse of the transmitter 1 by a time equal to the duration of one gate τ _p in the direction of movement. The calculator 12 provides information about the current coordinate H 'and the instantaneous value of the vertical component of the speeds VV

In the proposed low-altitude device, the transmitter modulator 1 ensures its operation in a pulsed mode with a probe pulse repetition rate of 1 MHz and a duration of no more than 10 ns at half the amplitude of intensity, while the quantum yield of the radio frequency is 10 ¹² -10 ¹³ quanta per second, their average energy 60 keV, maximum up to 100-120 keV. The radiation pattern of the transmitter 2Ψ80 ^about .

 Impulses that have passed coincidence schemes arrive at programmable timers. After accumulation for a given time interval (accumulation cycle), the value corresponding to the number of incoming pulses is introduced into the microprocessor system via three independent channels. The work of the computer is controlled by a microprocessor. According to the program recorded in the ROM, the necessary calculations are performed with the output values. Depending on the result of the calculation, the control of the delay line is issued via a programmable parallel adapter. Through it, information about altitude and speed is transmitted to the control loop, or to a display or other device. The step of information accumulation is set depending on the requirements for the accuracy of measuring height and speed, and is 10-50 ms. This is due to the fact that when approaching aircraft, spacecraft, etc., as a rule, have a speed of 1-2, less often 3-5 m / s.

 Vertical speed measurement minimizes dynamic height error. The characteristics of the device allow collecting sufficient statistics for the accumulation cycle to implement the proposed algorithm without miscalculations. Current data values, as well as intermediate calculation results, are stored in RAM. The synchronization of all components of the calculator is carried out using a generator. The system controller for data and control buses generates signals that control the operation of the components of the calculator, and also increases the load capacity of the system data bus.

 In addition to eliminating the dynamic error of height measurement, the device allows you to obtain continuous information about the height, since a malfunction in the device is eliminated by using a bi-directional information comb, which is shifted, depending on the direction. Higher measurement accuracy is also achieved by eliminating the error associated with the position of the peak peak of the reflected signal inside the second strobe of the information comb, which takes into account the correction term of the calibration curve. An additional advantage of the device is the ability to measure the instantaneous value of the vertical component of the speed of movement.

Claims (2)

1. The method of measuring small heights, which consists in the fact that the reflector surface is irradiated with X-ray pulses, the reflected signals are recorded, characterized in that the entire range of measured heights is divided into K virtual gates of the same duration τ _page on a time scale and duration Cτ _p / 2 by the distance scale, where C is the speed of light, form an information comb of three strobes of the same type with a length of τ _p , adjacent to each other, rigidly tie them to the time axis and virtual gates, tracking the central strobe of the information comb and the corresponding number m, where m ≥ 2, on the virtual strobe scale so that the maximum of the reflected signal is in the central strobe of the information comb, determine the direction of movement to or from the reflector surface, calculate the number of pulses per cycle in each of the accumulation gates information comb N _{m - 1,} N _m, N _{m + 1} is multiplied by the empirical weighting coefficients K _{m - 1,} K _m, K _{m + 1} and at maximum displacement of tse tral comb strobe information in any of the extreme shift information comb scale strobes virtual _page by the value τ so that the maximum number of accumulated pulses strobes information comb considering weighting factors always located in the central gate, and calculating the current value of the height of the formula

where tgθ _{m is} the slope of the experimentally obtained calibration curves connecting the change in the number of accumulated pulses in two adjacent gates with an information comb m and m + 1 with a change in the distance to the reflector.  2. A device for measuring low altitudes, containing an x-ray transmitter, a detecting unit, a gate generator connected to one of two delay lines, characterized in that three coincidence schemes, three counters and a calculator are introduced, one of the delay lines is controllable, the other is multi-tap and connected to the first delay line, three outputs of the multi-tap delay line are connected to the first inputs of three matches, the second inputs of which are connected to the output of the detection unit, and the inputs of three matches connected respectively with three counters, each of which is connected to a computer, the output of which is connected to the control input of the controlled delay line.

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