SU1418917A1 - Cable length measuring apparatus - Google Patents

Abstract

The invention relates to telecommunications technology. The purpose of the invention is a no-j increase in measurement accuracy. The device contains r-r 1 variable frequency, current amplifier 2, indicator 3, synchronous detector (.SD) 6, frequency meter 10, decoder 12, motor 13 and 13, sampling and storage unit 14, measured cable 15. Device a phase shifter 4, a phase controller 5, a r-7 reference signal, a band-pass filter 8, an LED 9, a voltage comparator II are introduced. In order to increase the noise immunity and simplify the device, the reference signal of the LED 6 is manipulated in phase by means of the manipulator 5. Filter 8 eliminates the influence of interference, which may be present in the cable 15, on the measurement result. The setting frequency of the filter 8 is equal to the frequency of Mr. 7. The change in the sign of the voltage at the output of the LED 6 is allocated to the LED 9 and the comparator II, and via block I 13 allows the block 14 to memorize the critical values. Frequency measured by frequency meter-I0. In order to avoid counting ambiguity, an approximate cable length of 15 db. a priori known. 1 il. (L

Description

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;about

The invention relates to telecommunications engineering and can be used in the construction and reconstruction of cable lines, for example, to measure the length of a cable in amplifying sections of high-frequency transmission systems.

The purpose of the invention is to increase the measurement accuracy.

The drawing shows a structural electrical circuit of the proposed device.

The device for measuring the cable length contains a variable frequency generator I, current amplifier 2, indicator 3, phase shifter 4, phase handler 5, first synchronous detector 6, reference generator 7, band pass filter 8, second synchronous detector 9, frequency meter 10, comparator II voltage, the decoder 12, the element And 13, block 14 sampling and storage, measurable cable 15.

The device works as follows.

The signal from the alternating frequency generator 1 through the current amplifier 2 enters the measured cable 15. In the inconsistent mode, due to reflection from the far end of the measured cable 15 at some frequencies, called critical, its input resistance reaches its max. the share of the extremal (maximum ip minimum) value, and in argument the value close to zero. For-1 mapno in the most commonly used idle mode of the far end, the input resistance of the measured cable 15 is described by the expression:

 in

g ,, cth

(7):

where ZP is the wave impedance of

nii;

1 - the length of the measured cable 15;

j4 vC i /} - distribution coefficient;

0 - attenuation coefficient; / 5 - Phase coefficient. The voltage of the signal at the output of the first synchronous detector 6 due to the phase shifter 4, shifting the phase of the signal of the variable frequency generator 1 by 90 °, is proportional to the sine of the input resistance argument of the measured cable I5

YU

t5 30 dO

I89I72

(when I / - o has the maximum slope J, and changes its frequency when passing through the critical value. 5 To increase the noise immunity and simplify the device implementation, the reference signal of the first synchronous detector 6 is phase-controlled using phase manipulator 5. The band-pass filter 8 allows There is no need to eliminate the influence of interference, which may be present in the measured cable 15, on the measurement result. The tuning frequency of the bandpass filter 8 is equal to the generator frequency 7. The change of the voltage sign at the output of the first synchronous part The borer 6 (i.e., a change by 180 of the phase of the modulating voltage) is allocated by the second synchronous detector 9 and the voltage comparator 11 and, through the element 13, allows the block 14 to store the sample and storage values of the critical frequency measured by frequency meter 10 calibrated in meters according to the formula

nv

Af,

20

25

1 kp, n

30 do

kp. P

35

0

45

five

where 1 - indicator reading 3; V - propagation velocity

on the measured cable 5;

nth critical value

frequencies;

p "1,2 .. number of the critical frequency. In order to avoid the ambiguity of the reference, the approximate length of the cable to be measured 15 must be known a priori. The decoder 12 imposes on the AND 13 blocking signal when the frequency of the oscillator 1 frequency of the varying frequency extends beyond the vicinity of the selected critical frequency limited by the adjacent critical frequencies.

Claims (1)

Invention Formula A device for measuring the length of the cable, containing a series-connected variable frequency generator, a current amplifier whose output is the input of the first synchronous detector measured by the cables, a frequency meter connected in series, the input of which is connected to the output of the variable frequency generator, decoder, element I, unit sampling 31418917 and storage, the second input of which is the co-rator of the reference signal and the second input with the output of the frequency meter, and the display of the first synchronous detector, a cator, characterized in that, connected in series with a strip, in order to improve the accuracy of a measuring filter, whose input is connected rheni, a generator of the reference output of the first synchronous detector signal, connected in series to the detector, the second synchronous detector, phase shifter, the input of which is connected; the second input of which is connected to the output of the generator with the change of the generator's reference signal frequency and phase switch, Q is the voltage comparator, the output of which is the second input and output of which is connected to the second input of the elelenene, respectively, with the output of the generator I.