Introduction of cable performance, transmission parameters and related test elements

Table of Contents

Performance certification

Performance certification is mainly aimed at transmission performance, items are usually: conductor DC resistance, resistance imbalance, working capacitance, ground capacitance imbalance, characteristic impedance, attenuation, crosstalk (near end and far end), attenuation crosstalk ratio (far end crosstalk defense), echo loss, delay, delay difference, wavelength shortening (wave velocity ratio) and so on.

Security authentication

There are mainly structural testing, specific gravity, tensile test before and after aging, thermal deformation, cold bending, flexure, migration test, insulation resistance, voltage test, combustion test and so on.

Cable Classification

CM (communication), MP (multi-purpose), CL2 or 3 (current limiting), CATV (common TV antenna), etc.

Laying mode and combustion grade 

CMP– is laid in the ceiling interlayer and other places of forced ventilation, the fire resistance of the cable is the most stringent.

UL test method: UL910.

CMR– is laid in vertical shafts or elevators.

UL test method: UL1666.

CM (CMG)-all occasions except plenum and riser mainly refer to vertical bundle laying.

UL test method: 1160 of UL1581.

CMX– is laid vertically, which is equivalent to VW-1.

UL test method: 1080 of UL1581.

CMH– is laid horizontally.

Product Certification Mark

Usually, the icon can be used after it has been approved by a certification body.

Such as UL icon, C-UL icon, CSA icon, CCC logo, T-MARK, F-MARK and so on.

Characteristic impedance (wave impedance) 

The ratio of voltage to current at any point in an ideal circuit without reflection.

Uniform lines have inherent impedance.

It is determined by the primary parameters of the line and the frequency of the signal sent, and has nothing to do with the length of the line, the voltage and current transmitted and the connected load or equipment.

The characteristic impedance of the cable is very important for the impedance matching in the system.

The unit is “Ω”.

Attenuation

Attenuation characterizes the signal loss caused by the material of the circuit and so on.

It consists of two parts, one is the dielectric loss caused by the orientation motion of the dipole caused by the alternating electric field, and the other is the energy loss caused by the thermal magnetic eddy current on the conductor and the heating of the conductor.

Unit is “dB/m”.

After the sensitivity of the transmitting equipment and the receiving equipment is determined, the allowable attenuation of the line is confirmed.

The lower the line attenuation, the longer the communication distance.

Carrier communication can extend the communication distance by setting up a sound amplification station.

However, the communication distance is limited by the signal transmission time, so as not to affect the communication quality.

Reflection attenuation (echo loss)

Due to the influence of material, structural size and manufacturing process (uneven insulation discharge, eccentric traction wheel, uneven rotation of take-up and release wire) and other defects and dispersion, the distribution of impedance along the length is uneven.

When the electromagnetic wave is transmitted on the line, it will produce multiple reflections when it meets the uneven point. When the odd reflected wave returns to the transmitter, it will cause the change of the input impedance, the power change of the main wave signal, the fluctuation of the attenuation frequency characteristic and the signal distortion.

The even reflected waves form wake, lag and superimpose on the main wave, causing interference, especially when the pulse signal is transmitted, it will cause waveform distortion and signal distortion.

Especially when there is periodic non-uniformity, the impact is the most serious.

Far end crosstalk attenuation

The ratio of the transmission power of the main serial loop to the remote power of the serial loop is taken as the logarithm * 10 times as the unit of “dB”.

Attenuation crosstalk ratio (remote crosstalk defense)

The difference between the signal level received by the remote end of the serial loop and the crosstalk level strung to the receiving end.

When the main string is the same as the stranded circuit, it can be simplified to the difference between far-end crosstalk attenuation and attenuation.

It directly affects the error degree of the signal.

The influence of crosstalk depends on the relative magnitude of the received active signal and crosstalk power. Because the far-end signal is attenuated and the signal is relatively small at the near end, the crosstalk defense degree in communication engineering refers to the far-end crosstalk defense degree.

Influencing factors of interference parameters

For short cables (manufacturing length) below tens of KHz, the primary parameters are used to study; in high frequency or long cables, the primary parameters are difficult to determine, so the secondary parameters are used to measure the degree of crosstalk.

The primary interference parameters / secondary interference parameters are related to the relative position and structure of the loops, the communication mode, the structural uniformity, the quality of the material used, the loop length and the transmission frequency of the signal.

Delay / delay difference

The unit of time required for electromagnetic wave propagation under certain line length is “ns/m”.

For the core wires within or between wire pairs, the difference of electromagnetic wave propagation delay.

Wave velocity ratio

The ratio of the propagation velocity of electromagnetic waves in the medium of a cable to that in a vacuum. 

Conductor resistance

The length and size of the sample are specified, and the resistance is measured by DC bridge, which is converted into 20℃ DC resistance by the relationship of temperature coefficient.

Working capacitance

It was tested by LCR tester.

Delay

It can be tested by TDR or Network Analyzer.

Crosstalk, Characteristic impedance, Echo loss, Wavelength shortening

They can be tested by Network Analyzer.

Conductor tensile test

Specified sample length and size; marking line; tensile speed; calculated elongation.

Insulation resistance

The use of high resistance meter to test.

(with shielding) directly measure the insulation resistance between the conductor and shield of the core wire; (without shielding) the insulated core wire should be immersed in a water and the water bath is used as the electrode to test.

Voltage test

The voltage tester is used to test.

(with shielding) directly measure the insulation resistance between the conductor and shield of the core wire; (without shielding) the insulated core wire should be immersed in a water and the water bath is used as the electrode to test.

Aging test

Specified sample length and size, placement mode in the aging box, aging temperature and time, air exchange requirements of the aging box, storage time at room temperature.

Stretch / cold stretch

Specified sample length and size; (cooling temperature and time), tensile speed; calculated elongation.

Tensile strength test

Specified sample length and size; tensile speed; breaking force, nominal cross-section; calculation of tensile strength.

Heating deformation test

Preheating temperature and time, load weight, aging temperature and time, cooling mode, measuring deformation; calculating relative deformation.

Thermogravimetric test

Specified sample length and size; drying time at room temperature, measuring weight; aging temperature and time; drying time at room temperature, measuring weight again; calculating relative weight loss.

Thermal stability test

Incubator temperature and time, weight; test PH constant time; test PH change to the specified value time.

Thermal shrinkage test

Specified sample length and size; aging temperature and time; maximum allowable shrinkage length.

Low temperature shock / thermal shock

Specified sample length and size; mandrel diameter, winding coil number, winding speed, (low temperature or aging) temperature and time; directly judge whether the sample has cracks or do voltage test to determine.

Low temperature / hot winding test

Specified sample length and size; temperature and time; mandrel diameter, winding mode, winding coil number; directly judge whether the sample has cracks or do voltage test to determine.

Cold bending test

Low temperature temperature and time, winding speed and number of laps.

Bending test

Bending radius, load, swing angle, swing speed.

Hardness test

Shore A for soft materials, Shore D for semi-hard materials, Brinell hardness method for hard materials).

Migration resistance test

Specified sample length and size, ABS or PS absorption plate size; sample sandwiched between absorption plates, bearing weight on the absorption plate; aging temperature and time; observe traces and discoloration on the absorption plate.

Adhesion test

Specified sample length and size, tensile speed.

Oil resistance test

Specified sample length and size; temperature and time of immersion in specified type of test oil; storage time at room temperature; test tensile strength and elongation; calculation of residual rate.

Color check

Natural light or light box (cold white fluorescence, sunlight, horizontal sunlight, ultraviolet light) or with a line sequence detector.

Specific gravity test, foaming test

Weigh the weight of the sample suspended by copper wire in air, weight in water (including copper wire), weight in water of copper wire; use the equal volume formula to calculate the specific gravity.

Horizontal / vertical / vertical bracket combustion test

Different test devices, different test methods, different judgment methods.

There are the following related factors:

That is, the specified length and size of the sample;

Sample prevention mode, distance from flame;

Layout marks on the sample or cotton requirements under the sample;

Flame height temperature requirements, combustion angle, combustion time; combustion time interval, combustion times;

Through the flame burning speed or the degree of damage to the Mark and whether to ignite cotton to determine whether it is passed or not.

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