What kind of cable is used for communications such as RS485?

1. Search for answers on the Internet: First, ensure impedance matching (Z0=120Ω), and then select different model specifications based on the specific communication rate, transmission distance, wiring environment, and installation method. Many people use cables with polyvinyl chloride insulation such as RVVPS, RVVP, RVSP, and KVVP to transmit digital signals, which is incorrect! According to the letter designation: RVV refers to a flexible cable with copper conductors, polyvinyl chloride insulation and sheathing, and no shielding. RVVPS--Soft cable with copper core, polyvinyl chloride insulation and sheathing, and copper wire braided overall shielding. RVSP--Copper core, PVC insulated, stranded copper wire with braided shield; no sheath. As is well known, although it is inexpensive, polyvinyl chloride PVC is a material with high attenuation. In addition, for cables like these, only primary parameters such as resistance, voltage tolerance, and current-carrying capacity are taken into account; therefore, if the transmission line equations are applied, these parameters will not meet the communication requirements. It may work for low speeds and short distances, but it is unsuitable for high-speed, long-distance, multi-node bus communication; in such cases, fieldbus cables with impedance matching should be used. Fieldbus cables are designed based on transmission line equations; they are transmission components that require secondary parameters such as characteristic impedance and attenuation value. Using dedicated RS485 bus cables with impedance matching and low attenuation is more conducive to ensuring reliable communication. ※ The general-purpose field bus series of cables consist of twisted-shielded cables with a characteristic impedance of 120Ω, which are widely used in buses such as RS485/422 and CANBUS. There are many different specifications for these cables; please provide details such as the cable installation environment, communication speed, and maximum transmission distance without repeaters. We will then recommend the most suitable product based on these specific conditions. The following is generally recommended: unshielded twisted pair cable of the STP-120Ω type (for RS485 & CAN), with one pair of 20 AWG wires; the outer diameter of the cable is around 7.7 mm, and it has a blue jacket. Suitable for indoor, pipeline, and general industrial environments. When in use, one end of the shielding layer must be grounded! It is an unarmored twisted-shielded cable, STP-120Ω (for RS485 & CAN), with 1 pair of 18 AWG wires; the outer diameter of the cable is around 8.2 mm, and it has a gray jacket. Suitable for indoor, pipeline, and general industrial environments. When in use, one end of the shielding layer must be grounded! It is a armored twisted-pair shielded cable, ASTP-120Ω (for RS485 & CAN), with 1 pair of 18 AWG wires; the outer diameter of the cable is around 12.3 mm, and it has a black jacket. It can be used in areas with severe interference, frequent rodent problems, as well as those with requirements for lightning protection and explosion prevention. When in use, it is recommended to ground both ends of the armored layer, and one end of the innermost shielding layer as well! Devices such as frequency converters, power cables, transformers, and high-power motors often generate low-frequency interference, and this type of interference cannot be eliminated by using cables with shielding layers made of highly conductive materials – this includes even originally imported cables. Only shielding layers made of highly magnetic materials (such as steel strips or wires) can effectively suppress low-frequency interference. The most common method is to cover the cable with a steel tube, or to use armored cables made of materials with high magnetic permeability – ASTP-120Ω (for RS485 & CAN), 1 pair, 18 AWG; the outer diameter of such cables is around 12.3 mm. It can be used in areas with severe interference, frequent rodent problems, as well as those with requirements for lightning protection and explosion prevention. When in use, it is recommended to ground both ends of the armored layer, and ground one end of the innermost shielding layer! Terminal resistors (usually 120Ω) should be added if the transmission distance exceeds 300 meters. 2. In practice, for 485 communication cables used over short distances, at conventional baud rates, and in environments with low electromagnetic interference, ordinary shielded twisted pair cable is generally sufficient. 3. PROFIBUS consists of three compatible parts, namely PROFIBUS‑DP, PROFIBUS‑PA, and PROFIBUS-FMS. Among them, PROFIBUS‑DP/PROFIBUS-FMS uses RS485 transmission technology, with RS485 cables as the transmission medium ； PROFIBUS‑PA uses the IEC1158‑2 transmission technology, with a shielded twisted pair cable having a characteristic impedance of 100Ω as the transmission medium. The PROFIBUS-DP communication cable should be a twisted-shielded cable with a characteristic impedance of 150Ω; at a communication rate of 12 Mbps, the transmission distance can reach 90 meters. The physical layer of PROFIBUS—DP remains RS485; in practical use, most PROFIBUS—DP communication rates do not reach such high levels, and the transmission distance is well beyond 90 meters ； Therefore, a cable with a characteristic impedance of 120Ω can meet the requirements of PROFIBUS-DP communication in most cases. 4. Foundation Fieldbus is commonly referred to as FF Fieldbus; it is divided into two levels of buses: H1 and H2. H1 uses a fieldbus physical layer that complies with the IEC 61158‑2 standard ； H2 uses high-speed Ethernet for its physical layer. 　　The main electrical characteristics of the physical layer of the H1 fieldbus are as follows: it uses bit-synchronized digital transmission ； The transmission baud rate is 31.25 kb/s ； Driving voltage 9–32VDC ； Signal current ±9mA ； Cable type shielded twisted pair ； The wiring topology can be linear, tree-shaped, star-shaped, or hierarchical ； Cable length is less than or equal to 1900m (without a repeater) ； The length of the branch cable is 30–120 m ； The number of interface devices is 32 or less (when there are no repeaters) ； The number of available repeaters is 4 or less ； Applicable explosion protection methods include intrinsically safe explosion protection methods, etc. 　　The H1 fieldbus provides power to multiple field instruments and enables two-way digital communication over a shielded twisted pair cable. The H1 network cards installed in the control system are typically responsible only for bidirectional communication with the field instruments. The power supply for the bus must be provided by a dedicated FF distributor. The H1 bus is organized in segments; each H1 network card has two ports, with each port connected to one segment, and each segment requires an FF distributor. A termination resistor is also required at each end of the bus to eliminate echoes from high-frequency signals. A list of some simple explanations; nothing too elaborate. Just take a look – it might help you gain some insights.

I’ve learned quite a bit, but I still don’t know much about bus cables; I need to learn more in the future*. Current enterprises mainly use traditional methods for signal transmission, relying on control cables.

RS485 cables come in 2-core and 4-core versions, with several different wire diameters; they may also be shielded or armored

We are Shanghai Canshengte Cable, a manufacturer specialized in the production of special cables. The following is an introduction to RS485 communication cables: In applications such as motor control and actuation control, RS485 cables benefit from advantages including immunity to noise, a wide common-mode range, an appropriate data transmission rate, and the ability for multi-point transmission; these reasons have led to its widespread adoption in the industry. Other application areas also make use of this communication technology due to the advantages of RS-485, including process control networks, industrial automation, remote control, building automation, and security systems. Since these applications require stable data transmission over relatively long distances, they all use RS-485 technology. In industrial control applications, since the motor control system includes a mechanical brake for the motor that generates high electrical noise and operates at high current levels, safety and reliability must be taken into account when designing the communication paths for the controller. The RS485 cable is suitable for transmitting both audio signals and railway signals that are installed fixedly; it boasts excellent interference resistance. It can be used with a single pair or multiple pairs simultaneously, and it performs particularly well when transmitting multiple signals. It can also be used to transmit power to some extent. This describes the usage characteristics and structure of railway signal cables. For RS-485 communication cables, twisted pair is sufficient in general applications, but shielded twisted pair can be used in environments with higher requirements. The maximum transmission distance of an RS485 cable can reach 1200 meters, but in practical applications, the transmission distance varies depending on the transmission characteristics of the chips and the cables used.