-----------------Extended reading
Choose industrial communication cable, first meet the impedance (Z=12Ω) matching, and then according to.
Many people use cables with PVC insulation media such as RVVPS, RVVP, RVSP and KVVP to transmit digital signals, which is wrong! Explain by letter:
rvv-copper conductor PVC insulated and sheathed flexible cable without shielding.
rvvps-copper conductor PVC insulated and sheathed copper wire braided total shielded flexible cable.
rvsp-copper conductor PVC insulated stranded copper wire braided shielded wire without sheath.
kvvp-copper conductor PVC insulated and sheathed copper wire braided total shielded control cable.
as we all know, although the price is low, PVC is a high attenuation material. In addition, the cable itself only considers the primary parameters such as resistance, withstand voltage and current carrying capacity, so if it is considered according to the transmission line equation, these can not meet the communication requirements. Low speed and short distance may be possible, but high speed, long line and multi-node bus communication is difficult. At this time, field bus cables with impedance matching should be used.
Fieldbus cable is designed according to the transmission line equation, and has transmission elements with secondary parameters such as characteristic impedance and attenuation value.
※ Universal Fieldbus Series Cable
(PatentNo.: 21 2 559128.9 Beware of counterfeiting)
twisted-pair shielded cables with characteristic impedance of 12Ω are widely used in RS485/422, CANBUS and other buses. There are many specifications of this series of cables. Please provide cable laying environment, communication rate, maximum relay-free transmission distance and other parameters, and we will recommend the most appropriate products according to the specific situation. General recommendations are as follows:
unshielded twisted pair shielded cable STP-12Ω (for RS485 &; CAN) one pair 2 AWG, cable outer diameter about 7.7mm, blue sheath. Suitable for indoor, pipeline and general industrial environment. When in use, one end of the shielding layer is grounded!
unshielded twisted pair shielded cable STP-12Ω (for RS485 &; CAN) one pair 18 AWG, cable outer diameter is about 8.2mm, with gray sheath. Suitable for indoor, pipeline and general industrial environment. When in use, one end of the shielding layer is grounded!
armored twisted pair shielded cable ASTP-12Ω(for RS485 &: CAN) one pair 18 AWG, cable outer diameter is about 12.3mm, with black sheath. It can be used in places with serious interference, frequent rodent damage and lightning protection and explosion protection requirements. When in use, it is recommended that both ends of the armor layer are grounded, and one end of the innermost shield is grounded!
Frequency converters, power cables, transformers, high-power motors, etc. are often accompanied by low-frequency interference, which cannot be solved by cables with high conductivity materials as shielding layers, including original imported cables. Only the shielding layer made of high permeability materials (such as steel strip and steel wire) can effectively suppress low frequency interference.
the most common method is to put a steel tube on the cable or directly use an armored cable made of high magnetic permeability material-astp-12ω (for RS485 &: CAN) one pair 18 AWG, with an outer diameter of about 12.3mm. It can be used in places with serious interference, frequent rodent damage and lightning protection and explosion protection requirements. When in use, it is recommended that both ends of the armor layer are grounded, and one end of the innermost shield is grounded!
it is very important to lay cables outdoors for lightning protection! The equivalent interference frequency of lightning is about 1k, which also belongs to low frequency interference.
article 6.3.1 of code for lightning protection design of buildings (GB 557-94): ...........................................................................................................................................
GB 5217-27 Cable Design Code has a similar expression. Search for "Industrial Automation Series Integrated Cable Solution" and enter the China Industrial Control Network Forum for viewing and communication.