Fieldbus cable, also known as bus cable. According to the International Electrotechnical Commission IEC61158 standard definition, fieldbus refers to a digital, serial, multi-point communication data bus between field devices installed in the manufacturing process area and automatic control devices in the control room. There are many types of communication media used to connect on-site devices, each with its own unique performance characteristics that have a significant impact on aspects such as data transmission rate, communication distance, reliability of data transmission, cost, and ease of installation and maintenance. The main communication media include bus cables, optical cables, microwave, infrared, etc. Among them, bus cables are commonly used.

Generally, control cables only need to consider Ohm's law, while fieldbus cables need to consider quadratic parameters according to the transmission line equation. In essence, bus cables should belong to the category of digital transmission cables, and the more common name is "twisted pair cables". For twisted pair cables, users are most concerned about several indicators that characterize their performance. These indicators include attenuation, near end crosstalk, impedance characteristics, distributed capacitance, and DC resistance.

Twisted pair cables are cables that are familiar to both users and manufacturers, and are classified into five different quality models. The five types of cables are introduced as follows:

Class 1: Mainly used for transmitting voice. Class 1 standards are mainly used for telephone cables before the early 1980s and are not used for data transmission.

Category 2: Transmission frequency of 1MHz, used for voice transmission and data transmission with a maximum transmission rate of 4Mbps, commonly found in old token networks that use the 4Mbps standard token passing protocol.

Category 3: Refers to the cables currently specified in ANSI and EIA/TIA568 standards. The transmission frequency of this cable is 16 MHz, used for voice transmission and data transmission with a maximum transmission rate of 10 Mbps, mainly for 10 base-T.

Category 4: This type of cable has a transmission frequency of 20 MHz and is used for voice transmission and data transmission with a maximum transmission rate of 16 Mbps. It is mainly used for token based LANs and 10 base-T/100base-T.

Category 5: This type of cable has increased winding density and is covered with a high-quality insulation material. It has a transmission frequency of 100 MHz and is used for voice transmission and data transmission with a maximum transmission rate of 100 Mbps. It is mainly used for 100 base-T and 10 base-T networks and is a commonly used Ethernet cable.

So bus cables should be said to have started from Class 3 and have now developed into Class 6 and Class 7. However, the transmission frequency of symmetrical twisted pair cables has a limit and is unlikely to continue to develop. As long as the cost-effectiveness is higher, fiber optic cables, microwave, infrared, and laser communication media will gradually become more efficient. Twisted pair cables are divided into two categories: shielded twisted pair cables and unshielded twisted pair cables. In these two categories, its impedance is divided into 100 ohm cables, dual body cables, large logarithmic cables, 150 ohm shielded cables, etc. There are various specific models available.