CN110345887B - Network cable length measuring method based on TDR technology adaptive range - Google Patents
Network cable length measuring method based on TDR technology adaptive range Download PDFInfo
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- CN110345887B CN110345887B CN201910013895.5A CN201910013895A CN110345887B CN 110345887 B CN110345887 B CN 110345887B CN 201910013895 A CN201910013895 A CN 201910013895A CN 110345887 B CN110345887 B CN 110345887B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B15/00—Measuring arrangements characterised by the use of electromagnetic waves or particle radiation, e.g. by the use of microwaves, X-rays, gamma rays or electrons
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
Abstract
The invention discloses a network cable length measuring method based on a TDR (time domain reflectometry) technology adaptive range, which is characterized in that a narrow pulse wave is sent from one end of a cable, the signal is reflected when reaching the opposite end of the network cable, the time for receiving the reflected pulse is calculated, and the transmission speed of the narrow pulse wave is multiplied by the time for receiving the reflected pulse, so that the length of the network cable is obtained. The invention can give consideration to the length measurement in a wider range by adopting a cyclic measurement mode of a plurality of emission pulse width grades, and can well solve the problems of large blind area and small measuring range caused by only adopting a single emission pulse width grade in the existing products on the market.
Description
Technical Field
The invention discloses a network cable length measuring method, in particular to a self-adaptive measuring range based on a TDR (time domain reflectometry) technology
The network cable length measuring method belongs to the technical field of Time Domain Reflectometry (TDR) measurement.
Background
With the use of the internet becoming more and more widespread, the usage amount of the network cable also becomes larger and larger, and for network cable manufacturers, sellers or engineering construction, the network cable needs to be frequently communicated with the network cable, and besides the specification, quality and on-off condition of the wire, the length of the cable used by the network cable also needs to be known sometimes. The simplest mode of measuring the length of the network cable is to adopt a measuring tape to measure, and the mode efficiency of measuring by adopting an original measuring tape is very low, so that the method is temporary emergency, can not be applied to engineering construction on a large scale, and at the moment, an electronic product is required to carry out automatic measurement, thereby improving the working efficiency.
Early electronic network cable length measuring equipment adopts a resistance principle to measure, and the hardware cost and the software cost of the mode are low, but the biggest disadvantage is that a user needs to know the wire resistance of unit length (namely the resistance of a unit length of an electric wire) of each wire type in advance, and needs to find the other end to connect a connecting receiver to realize the measurement, and the two obviously are inconvenient for practical operation; at present, a plurality of measuring instruments are also arranged on the market to measure by using the capacitance principle, and the method has the advantages that the measurement can be carried out without finding the other end of the cable, but the influence of the cable material and the use environment (temperature, humidity and the like) is great, and the short-circuit position point cannot be accurately measured.
Disclosure of Invention
Aiming at the defect that the network cable measurement in the prior art is not convenient and accurate enough, the invention provides a network cable length measurement method based on the TDR technology adaptive range.
The technical scheme adopted by the invention for solving the technical problems is as follows: a network cable length measuring method based on a TDR technology self-adaptive range is characterized in that a narrow pulse wave is sent out from one end of a cable, the signal is reflected when reaching the opposite end of the network cable, the time for receiving the reflected pulse is calculated, the transmission speed of the narrow pulse wave is multiplied by the time for receiving the reflected pulse to obtain 2 times of the length of the network cable, and the length is divided by 2 to obtain the length of the network cable.
The technical scheme adopted by the invention for solving the technical problem further comprises the following steps:
the waveform period of the narrow pulse wave is 20 ns-200 ns.
The narrow pulse wave is a fast edge signal sent by a step source.
The network cable length measuring method comprises the following steps:
step S1, transmitting by using the transmitting wave of transmitting pulse width level 1, and acquiring the acquired data after the receiving end finishes acquiring the signal;
step S2, calculating an average value: skipping the transmitting wave part of the transmitting pulse width grade, and averaging the subsequent wave forms to obtain an AVG (average voltage regulator) which is used as an analysis threshold value;
step S3, finding out a rising point TD1, a peak point TD2 and a falling point TD3 of the emission wave according to the comparison with the mean AVG;
step S4, presetting an open-circuit threshold multiplying factor R as a basis for judging the effectiveness of the reflected wave;
step S5, according to the comparison between the reflected wave and the average value AVG, finding out the rising point RD1, the peak point RD2 and the falling point RD3 of the reflected wave;
step S6, comparing the peak value RD2 of the reflected wave with a set threshold value, if the former is larger than the latter, the emission pulse width grade is considered to be effective, at the moment, the total time used for signal transmission back and forth is obtained according to (RD 1-TD 1), and then whether the time accords with the effective measurement range of the emission pulse width grade is judged, if the time accords with the report result, if the time does not accord with the effective measurement range, the measurement is retested for 3 times, and if the time fails for 3 times, the measurement is determined to fail; if the former is smaller than the latter, the transmission pulse width level is considered to be not consistent with 3, the next transmission pulse width level is replaced, the step S1 is skipped to be repeatedly executed, and the measurement is considered to be failed until the last level fails, which indicates that the situation is possible that no wire is connected or the cable exceeds the maximum measurement range.
The preset open circuit threshold multiplying power R is 1.25.
The network cable length measuring method further comprises a step S0, wherein the step S0 comprises the following sub-steps:
step S0-1, measurement of alignment: carrying out on-off test of the line sequence, finding out the connection relation of each line core, respectively finding out two conditions of short circuit and open circuit, recording the on-off condition, and preparing for later length measurement and reflection waveform analysis;
step S0-2, initializing length measuring environment: acquiring the number of wire cores of the wire according to the type of the wire, acquiring the corresponding relation between the hardware channel number and the wire core number, and opening a length measurement control end signal;
step S0-3, the process proceeds to step S1, and length calculation is performed.
The step S0-1 is followed by the following steps:
step S0-1', according to the judgment of the line alignment result of the step S0-1, the lengths of the short circuit condition and the open circuit condition are respectively measured;
step S0-1 ″, if the line 1 is open-circuited, the line 1 is selected as the transmitting channel, the line 2 is selected as the receiving channel, the lines 1 and 2 are a set of twisted pair lines, and one-to-one differential signal measurement is performed, if the line 1 is short-circuited, the line 1 is selected as the transmitting channel, and the short-circuited line is selected as the receiving channel for length measurement.
The invention has the beneficial effects that: the invention can give consideration to the length measurement in a wider range by adopting a cyclic measurement mode of a plurality of emission pulse width grades, and can well solve the problems of large blind area and small measuring range caused by only adopting a single emission pulse width grade in the existing products on the market.
The invention will be further described with reference to the accompanying drawings and specific embodiments.
Drawings
FIG. 1 is a schematic diagram of impedance discontinuity measured by TDR according to the present invention.
FIG. 2 is a diagram of a TDR signal transmission model according to the present invention.
FIG. 3 is a TDR waveform illustrating the actual open circuit condition of the present invention.
FIG. 4 is a TDR waveform illustrating the short circuit condition of the present invention.
FIG. 5 is a flow chart illustrating the operation of the present invention to measure the length of a channel cable.
Fig. 6 is a schematic diagram of a non-differential signal waveform.
Fig. 7 is a schematic diagram of differential signal waveforms.
Detailed Description
This embodiment is a preferred embodiment of the present invention, and other principles and basic structures are similar to the embodiment
The same or similar, are within the scope of the invention.
TDR is the abbreviation of english Time Domain Reflectometry, and the chinese name is Time Domain reflectometer, is the main instrument of measuring transmission line characteristic impedance, and TDR mainly comprises the triplex: when impedance changes (namely differential mode impedance discontinuity) occur in a transmission path, part of energy can be reflected, and the rest of energy can continue to be transmitted.
In the invention, the method for measuring the length of the network cable based on the TDR technology adaptive range mainly comprises the steps that a line measuring instrument sends out a narrow pulse wave from one end of a cable (in the embodiment, the narrow pulse wave is in ns level, usually 20 ns-200 ns), when the signal reaches the opposite end of the network cable, because an opposite end open circuit (impedance is suddenly changed to infinity), the signal is reflected back, the instrument calculates the time for receiving the reflected pulse, and the longer the network cable is, the longer the pulse is, the longer the time of one round trip is, and therefore the length of the network cable can be calculated. In the implementation, a fast edge signal (i.e. a narrow pulse signal, a pulse with a pulse width of 20 ns-200 ns and an amplitude of 3.3 v) emitted by a step source (i.e. a signal generator) is injected into a transmission line to be tested, if the transmission line impedance is continuous, this fast edge step signal propagates forward along the transmission line, and when the transmission line experiences an impedance change (i.e., the end is open, the impedance suddenly changes to infinity, or the other end is connected with a resistor or inductor that does not match the cable resistance), a part of the fast edge signal sent by the step source is reflected back, and a part of the fast edge signal continues to propagate forward (in this embodiment, the fast edge signal is partially transmitted as long as the cable is in midway impedance mismatch, and if the cable is in an open circuit condition, the fast edge signal also includes impedance mismatch in an extreme condition, the transmitted signal is totally reflected back), the reflected signal is superposed to the injected step signal, and an oscilloscope (i.e., a signal sampler) can acquire the signal. Because the reflected signal and the injected signal have a certain time difference, the edge of the superposed signal acquired by the oscilloscope is stepped (namely, the reflected signal is superposed by the emitted signal to cause the step of the detected signal), and the step reflects the time relation of signal propagation and reflection and corresponds to the length of the transmission wire.
In this embodiment, the cable loaded with the narrow pulse wave is defined as a transmitting channel, i.e. a narrow pulse wave (ns level, time t1, i.e. duration of the narrow pulse wave t 1) is actively emitted from the transmitting channel, and an electrical signal is transmitted through the conducting wire and is reflected back to the transmitting end when the impedance on the wire is discontinuous. The time elapsed at this time is recorded as t2, the distance traveled by the signal can be calculated according to the propagation speed of the electrical signal on the conductor and the propagation time t2 (obtaining the length of 2 times of the network cable, and then dividing the length by 2 to obtain the length of the network cable), in order to accurately measure t2, the invention adopts the scheme that the FPGA is matched with the high-speed ADC for measurement, thereby improving the resolution of the measurement.
According to the characteristics of transmitting echo transmitted by a wire by a narrow pulse width electric wave signal (20 ns-200 ns), and the pulse
At a wire propagation speed of 100M/us (i.e., 1M/10 ns), if a sampling frequency of 300M is used (i.e., 3.33 ns)
Sampling an AD value), so theoretically its resolution is ± 0.33m, so it has a small measurement blind spot, within 33cm, i.e. it can measure the length of the network cable greater than 33cm using the invention), setting the measurable length range 2000m according to the slowest propagation speed 100m/us calculation, then AD sampling takes place: (2000/100) × 2=40 us.
In other words, the length of the network cable is calculated to be 2000m, namely the time t2 is 40 us.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The method comprises the following specific implementation steps:
step S1, pair line measurement:
the on-off test of the line sequence is carried out by utilizing a sampling mode of the resistor array (in specific implementation, a line sequence and an on-off test mode commonly used in the prior art can also be adopted), the connection relation of each line core is found out, two conditions of short circuit and open circuit (namely no short circuit) are respectively found out, the on-off conditions of the two conditions are recorded, and preparation is made for the following length measurement analysis of the reflection waveform;
step S2, initializing length measurement environment:
acquiring the number of wire cores of the wire according to the type of the wire, acquiring the corresponding relation between the hardware channel number and the wire core number, and opening a length measurement control end signal;
step S3, calculating the length, in this embodiment, step S3 includes the following sub-steps:
s300: according to the judgment of the line aligning result of the step S1, respectively measuring the lengths of the short circuit condition and the open circuit condition;
s301: selecting a transmitting channel and a receiving channel according to the characteristics of the network cable; in this embodiment, taking a twisted pair as an example, if the line 1 is in an open circuit state (i.e. they are not short-circuited), the line 1 is selected as a transmitting channel, the line 2 is selected as a receiving channel (the line 1 and the line 2 are a set of twisted pair, and the line 2 is used as a reference signal, i.e. V-) of the differential signal to perform one-to-one differential signal measurement (here, the differential signal is not a differential signal in a strict sense, please refer to fig. 6 and fig. 7), and if the line 1 is in a short circuit state, the line 1 is selected as a transmitting channel, and the short-circuited line thereof is selected as a receiving channel;
s302: according to the fact that reflected energy of transmitted waves with different widths in the same wire length is different, measurement is carried out by sampling different transmitted pulse width grade principles, firstly, transmitted waves with the transmitted pulse width grade 1 (namely the narrowest transmitted pulse width grade, in the embodiment, the transmitted pulse width grade adopts 3 transmitted pulse width grades which are respectively 20ns, 100ns and 200ns, wherein the narrowest pulse width refers to the transmitted waves of 20 ns) are transmitted, acquired data are obtained after the FPGA finishes signal acquisition, and then, waveform analysis is carried out in a step S303 or a step S304;
s303: and (3) analyzing an open circuit waveform, and if the line 1 is in an open circuit state, analyzing the open circuit waveform:
A. calculating the mean value: skipping the transmitting wave part of the transmitting pulse width grade, and averaging the subsequent wave forms to obtain an AVG (average voltage regulator) which is used as an analysis threshold value;
B. finding a rising point TD1 (the amplitude of the emission wave is the same as the average value AVG), a peak point TD2 and a falling point TD3 (the amplitude of the emission wave is the same as the average value AVG) of the emission wave according to comparison with the average value AVG;
C. presetting an open-circuit threshold multiplying power R (in the embodiment, an empirical value of 1.25 is adopted) as a basis for judging the effectiveness of the reflected wave;
D. according to the comparison between the reflected wave and the average value AVG, finding out an ascending point RD1 (the reflected wave amplitude is the same as the average value AVG), a peak point RD2 and a descending point RD3 (the reflected wave amplitude is the same as the average value AVG) of the reflected wave;
E. comparing the value of the peak point RD2 of the reflected wave with a set threshold (i.e. the product of the average AVG and the threshold multiplying factor R), if the former is larger than the latter, the emitting pulse width grade is considered to be valid, at this time, the total time used by the signal transmission back and forth is obtained according to (RD 1-TD 1), and then whether the time is in accordance with the effective measuring range of the emitting pulse width grade is judged (in the embodiment, in the 1 st grade, 20ns, because the emitting pulse width is small, the corresponding energy is also small, the measurable range is also small, the theoretically effective measuring range is 5 m-50 m, if the 1 st grade measuring result is used, the measuring result is considered to be normal, if the effective measuring range is exceeded, if 100m is detected, the actual situation is obviously violated, the retest is required, the 2 nd effective measuring range is 30-250 m, the 3 RD effective measuring range is 200-950 m, the measuring range can refer to the effective measuring distance of the TDR technology), if the result is in line with the upper layer result, the upper layer result is informed, otherwise, the test is repeated for 3 times; if the former is smaller than the latter, the emission pulse width grade is considered not to be consistent, the next emission pulse width grade is replaced, the step S301 is skipped to and repeatedly executed until the last grade fails, the measurement is considered to fail, and the situation is that no wire is connected or the cable exceeds the maximum measurement range possibly;
s304: if the line 1 and the line 2 are in a short-circuit state, identifying according to the TDR waveform characteristics of the short-circuit condition, and analyzing reflected waves in the negative direction of the waveform mean value;
s305: analyzing a short circuit waveform, wherein the analysis process is basically similar to the analysis process of the open circuit condition of S303, but a preset threshold line is arranged below a mean value line;
according to the calculation principle of L = v.t, wherein v is the propagation speed of the electric signal in the conductor, t is the propagation time, and L is 2 times of the length of the network cable, the length of each cable can be calculated respectively.
The invention can give consideration to the length measurement in a wider range by adopting a cyclic measurement mode of a plurality of emission pulse width grades, and can well solve the problems of large blind area and small measuring range caused by only adopting a single emission pulse width grade in the existing products on the market.
Claims (6)
1. A network cable length measuring method based on TDR technology adaptive range is characterized in that: the method for measuring the length of the network cable is characterized in that a narrow pulse wave is emitted from one end of a cable, the signal is reflected when reaching the opposite end of the network cable, the time for receiving the reflected pulse is calculated, the transmission speed of the narrow pulse wave is multiplied by the time for receiving the reflected pulse to obtain 2 times of the length of the network cable, and the length of the network cable is obtained by dividing the length by 2, and the method for measuring the length of the network cable comprises the following steps:
step S1, transmitting by using the transmitting wave of transmitting pulse width level 1, and acquiring the acquired data after the receiving end finishes acquiring the signal;
step S2, calculating an average value: skipping the transmitting wave part of the transmitting pulse width grade, and averaging the subsequent wave forms to obtain an AVG (average voltage regulator) which is used as an analysis threshold value;
step S3, finding out a rising point TD1, a peak point TD2 and a falling point TD3 of the emission wave according to the comparison with the mean AVG;
step S4, presetting an open-circuit threshold multiplying factor R as a basis for judging the effectiveness of the reflected wave;
step S5, according to the comparison between the reflected wave and the average value AVG, finding out the rising point RD1, the peak point RD2 and the falling point RD3 of the reflected wave;
step S6, comparing the peak value RD2 of the reflected wave with a set threshold value, if the former is larger than the latter, the emission pulse width grade is considered to be effective, at the moment, the total time used for signal transmission back and forth is obtained according to (RD 1-TD 1), and then whether the time accords with the effective measurement range of the emission pulse width grade is judged, if the time accords with the report result, if not, the time is retested for 3 times, and if the time is failed for 3 times, the measurement is judged to be failed; if the former is smaller than the latter, the transmission pulse width grade is considered to be not consistent, the next transmission pulse width grade is replaced, the step S1 is skipped to be repeatedly executed, and the measurement is considered to be failed until the last grade fails, which indicates that the situation is possible to be that no wire is connected or the cable exceeds the maximum measurement range.
2. The network cable length measuring method based on the TDR technology adaptive range according to claim 1, wherein the waveform period of the narrow pulse wave is 20 ns-200 ns.
3. The network cable length measuring method based on TDR technology adaptive range according to claim 1, characterized by: the narrow pulse wave is a fast edge signal sent by a step source.
4. The network cable length measuring method based on TDR technology adaptive range according to claim 1, characterized by: the preset open circuit threshold multiplying power R is 1.25.
5. The network cable length measuring method based on TDR technology adaptive range according to claim 1, characterized by: the network cable length measuring method further comprises a step S0, wherein the step S0 comprises the following sub-steps:
step S0-1, measurement of alignment: carrying out on-off test of the line sequence, finding out the connection relation of each line core, respectively finding out two conditions of short circuit and open circuit, recording the on-off condition, and preparing for later length measurement and reflection waveform analysis;
step S0-2, initializing length measuring environment: acquiring the number of wire cores of the wire according to the type of the wire, acquiring the corresponding relation between the hardware channel number and the wire core number, and opening a length measurement control end signal;
step S0-3, the process proceeds to step S1, and length calculation is performed.
6. The method for measuring the length of the network cable based on the TDR technology adaptive range, according to claim 5, is characterized in that: the step S0-1 is followed by the following steps:
step S0-1', according to the judgment of the line alignment result of the step S0-1, the lengths of the short circuit condition and the open circuit condition are respectively measured;
step S0-1 ″, if the line 1 is in an open circuit state, the line 1 is selected as a transmitting channel, the line 2 is a receiving channel, the line 1 and the line 2 are a set of twisted pair lines, and one-to-one differential signal measurement is performed, and if the line 1 is in a short circuit state, the line 1 is selected as a transmitting channel, and the short circuit line is selected as a receiving channel for length measurement.
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