SU911371A1 - Method of measuring delay time - Google Patents

Description

(54) METHOD OF MEASURING DELAY TIMES

.,.

The invention relates to a measurement technique and can be used to measure a delay, for example in electrical, ultrasonic delay lines, to measure the speed of propagation of ultrasonic oscillations in various media, etc.

Methods are known for measuring the delay time based on measuring the transit time of a video or radio pulse signal P.

The disadvantage of these methods is their limited accuracy, especially when measuring short delay times, when the magnitude of the latter becomes comparable with the pulse duration, and also due to the instability of the leading edge of the pulse.

Methods based on the use of amplitude-modulated continuous oscillations are also known. The parameter recorded is the phase shift of the envelope of the detected, e.g. ultrasonic signal, relative to the electrical excitation voltage 21.

The disadvantage of these methods is low accuracy due to low sensitivity.

The closest technical solution is as follows. Two sequences of phase-coherent high-frequency radio pulses are applied to the input of the delay line. The delay between the sequences is chosen so that the arrival time at the receiving transducer (output of the delay line) of the first reflected pulse of the second sequence coincides with the moment of arrival of the second reflected pulse of the first sequence. Then, re-tuning the master oscillator in frequency (Meng filling frequency

20 radio pulses /, you can find a whole series of such frequency points, in which all, except for the first pulse of the first sequence, will be 3 rrrhfsr on the receiving center-ishagele imiulmis, 1 pogl / IITgeliost IlpoitcjiH measuring a number of such null lacTOTinitx points, the number - the value of the delay is 3, if the iipniniMaeNtbiri signal of the second reflected pulse of the second and subsequent IKI of the entireness is written in the form U rcis niuii + dL), Cl) then the incoming) 1st signal of the second reflected pulse of the first sequence will be (excluding attenuation and losses due to reflection and, cs nIviJtto.l) + mp4dL,) where t is the time, W is the circular frequency of filling of the radio pulse, f is the delay time, the phase shift when the pulse is reflected from the sample interface to converter, and the amplitude of the signal at the receiving JOU-d converter is + Q dL cOЕCu) t-). , W From the last relation it can be seen that Under the condition -.- v - - -, the received signal will be equal to zero. Determining several values, and considering 4 (t is independent of frequency, you can then calculate the delay time T., Signal amplitude in the ratio Sz) is u -lcjcosCuj -V (5 The error in determining the frequency satisfying condition (4), is determined by the sensitivity the signal amplitude meter U. You can write tf and IdCOS () where the sensitivity of the signal meter and, (the corresponding error in determining circular purity. Thus, the ratio (b) puts a fundamental accuracy on the accuracy of the time) 1I delay ki.Ishk -.tvit "lr but cHDianoB is fully quenched ich-ria 101 i, wht 4 they always exhibit distortion and are never completely and phase or antiphased relative to each other. Emissions remain due to inaccurate coincidence of the shape of pulse fronts. It is necessary to know the magnitude of the phase shift M At each of the operating frequencies, but practically when operating at high frequencies and in a wide frequency band, this is difficult to achieve. The purpose of the invention is to improve the accuracy of the measurement of the delay time. This goal is achieved by the fact that, according to the method of measuring the delay time, which consists in modulating a continuous high-frequency generator systole, feeding a delay line to the input, modulating a continuous signal in phase with a variable frequency, measuring the frequency of the phase modulation before and after the delay, they coincide, and the delay time is determined by its vespers. The delay LOTSHI input, the KOTopofi delay time needs to be measured, the signal is given%) + dl, (} where (t) is the phase of the modulated signal, cL is the initial phase. The signal at the output of the delay line, (t-1)) cL3, (} where T is the delay time. The phase difference of the signals at the output and input of the delay line is .u C lt-r) .Ч9) Considering that the difference frequency is climatic, the difference is hours, oscillations at the output and input of the delay line is determined by this m ratios 1 liuM azg di. m) Achsh1, 0) UI I 3i cjT i From this it can be seen that if the function Lf (t) is a periodic n period, it is associated with a chaggard time so it is damping. Tr-L,, g: / ;, /.V

then the frequency offset is zero. This circumstance lies at the basis of the conversion method.

Comparison of two close frequencies can be performed with great accuracy. For example, using the principle of multiplying the frequency from the input of the delay line by a factor of 9, and from the output of the delay line by a factor of IO, by their subsequent supply to bias, the difference frequency is multiplied by 10 times. Applying such an operation and once, we get a frequency shift multiplication of 4 to 10 times. This means that with the same sensitivity of the meter at the output, for example, frequency detector 6, the error in the definitions of the frequency corresponding to condition (P) will decrease by 10 times.

The advantage of the proposed method is that the type of the phase modulation signal, i.e. type of function

l (t), may not necessarily be harmonic, but any periodic function. This circumstance is of great importance in practical implementation from the point of view of simplification and

reduce the cost of the corresponding measuring device.

Claims (3)

1. Bergman L. Ultrasound. M., Ed. Foreign Literature, 1956, pp.216-225. 2. Brazhnikov N.I. Ultrasonic phase meter. M., Energie, 1968, pp. 125-129. 3.Williams J., Lamb.J.Journ. Acoust. Soc.Amer.30, 308, 1938 , (prototype).