Power cords are wires that carry electrical current. Usually, the way of current transmission is the point-to-point transmission. Power cords can be divided into AC power cords and DC power cords according to their uses. Usually, AC power cords pass through high-voltage alternating current wires. Due to the high voltage, such wires require a unified standard to obtain safety certification before they can be officially produced. The DC line basically passes direct current with lower voltage, so the safety requirements are not as strict as the AC line, but for safety reasons, countries still require unified safety certification.
Performance index of twisted pair in the power cord
For twisted pairs, users are most concerned about several indicators that characterize their performance. These indicators include attenuation, near-end crosstalk, impedance characteristics, distributed capacitance, DC resistance, etc.
What are the specifications of the power cord
(1) Attenuation
Attenuation is a measure of signal loss along with a link. The attenuation is related to the length of the cable, and as the length increases, the signal attenuation also increases. Attenuation uses "DB" as the unit and represents the ratio of the signal strength of the signal at the source transmitting end to the signal strength at the receiving end. Since attenuation varies with frequency, attenuation should be measured at all frequencies within the application range.
(2) Near-end crosstalk
Crosstalk is divided into near-end crosstalk and far-end crosstalk (FEXT). The tester mainly measures NEXT. Due to the existence of line loss, the influence of the magnitude of FEXT is small. Near-end crosstalk (NEXT) loss is a measure of signal coupling from one pair of wires to another in a UTP link. For UTP links, NEXT is a key performance indicator, and it is also one of the most difficult to measure accurately. As the signal frequency increases, its measurement difficulty will increase. NEXT does not indicate the crosstalk value produced at the near endpoint, it just indicates the crosstalk value measured at the near endpoint. This value varies with the length of the cable, the longer the cable, the smaller the value becomes. At the same time, the signal at the transmitting end will also be attenuated, and the crosstalk to other wire pairs will be relatively small. Experiments show that only the NEXT measured within 40 meters is more real. If the other end is an information socket farther than 40 meters, then it will generate a certain degree of crosstalk, but the tester may not be able to measure this crosstalk value. Therefore, it is best to perform NEXT measurements at both endpoints. Today's testers are equipped with corresponding equipment so that the NEXT value at both ends can be measured at one end of the link.
(3) DC resistance
TSB67 does not have this parameter. The DC loop resistance dissipates a portion of the signal and turns it into heat. It refers to the sum of the resistances of a pair of wires,
The DC resistance of the twisted pair of 11801 specifications shall not be greater than 19.2 ohms. The difference between each pair should not be too large (less than 0.1 ohms), otherwise, it indicates poor contact and the connection point must be checked.
(4) Characteristic impedance
Different from the loop DC resistance, the characteristic impedance includes resistance, inductive impedance, and capacitive impedance with a frequency of 1 to 100 MHz, which is related to the distance between a pair of wires and the electrical properties of the insulator.
Various cables have different characteristic impedances, while twisted pair cables are available in 100 ohms, 120 ohms, and 150 ohms.
(5) Attenuation Crosstalk Ratio (ACR)
In certain frequency ranges, the proportional relationship between crosstalk and attenuation is another important parameter that reflects cable performance. ACR is sometimes expressed as a signal-to-noise ratio (SNR: Signal-Noice ratio),
It is calculated from the difference between the worst attenuation amount and the NEXT amount. The larger the ACR value, the stronger the anti-interference ability. General system requirements are at least greater than 10 decibels.
(6) Cable characteristics
The quality of a communication channel is described by its cable characteristics. SNR is a measure of the strength of the data signal taking into account the interference signal. If the SNR is too low,
When the data signal is received, the receiver cannot distinguish between the data signal and the noise signal, which will eventually cause data errors. Therefore, in order to limit data errors to a certain range,
A minimum acceptable SNR must be defined.
Commonly used wire specifications for home improvement are: 1, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240, 300, 400, 500 square millimeters.
In addition: such as VV4X16MM2 is PVC insulated, PVC sheathed copper core cable, 4 cores, 16 square meters per core. BV1X95MM is a PVC insulated copper core wire with a cross-section of 95 square meters. RVV3X2.5MM2---Generally, R added at the back represents "multi-core flexible wire", and generally added in front is "ZR", which means flame retardant. VV is PVC insulated, PVC sheathed cable, BV is flat PVC sheathed cable, RVV is PVC insulated, and PVC sheathed flexible cable. The latter represents the extreme cross-sectional area of several copper wires.
Usually, the copper core wire can pass 4~6A current according to 1mm2, that is, 1mm2 can pass 5A current, that is, 1.1 kW, and so on; generally, 2.5 is used for air conditioners, 4 is used for cabinets, and 1 is used for lighting.
