Abstract
As 10BASE-T1L Ethernet emerges across various industries, more applications come to light, each bringing new challenges to be addressed to successfully deploy the technology. A common requirement is to support a wide range of cable types. In some cases, these cables have been used in legacy communication systems and are often found in existing installations. The flexibility of the cable definition in the 10BASE-T1L standard creates an advantage over other technologies by allowing the reutilization of such cables. This flexibility brings common questions such as whether 1 km can be achieved with any cable or whether performance is the same independently of the type of cable. Link performance and reach depend on the cable’s characteristics, which in turn, depend on the construction of the cable. This article summarizes the cable characteristics relevant to this technology, describes the dependency of cable reach as a function of these characteristics, and provides a list of cables that have been tested.
Introduction
Advanced Physical Layer and 10BASE-T1L
The advanced physical layer (APL) specification and the IEEE 802.3cg 10BASE-T1L specification are two different standards that are related but should not be used interchangeably. The IEEE 802.3cg standard defines the 10BASE-T1L physical layer for long reach Ethernet communication over single twisted pair independently of the application, while the APL standard adds extra specifications and definitions on top of the IEEE 802.3cg for the use of the same physical layer in process control applications in intrinsically safe environments. This means that any APL device is compliant with the 10BASE-T1L standard (the data layer, but not the power delivery over the data line), but not every 10BASE-T1L device is APL compliant.
The APL document comprises specifications for the data layer and system defini- tions, covering aspects such as electromagnetic compatibility (EMC) performance, cable shield connection, and network topology. For example, as shown in Figure 1, the APL specification defines two types of data links within the same network: the spur and the trunk. The spur links directly connect to the field devices and cannot exceed 200 m in length, operating at 1.0 V p-p transmission levels due to the intrinsically safe environments of the field devices. The trunk, which links field switches or connects upstream to the nearest power switch, can extend up to 1000 m and operates at 2.4 V p-p transmission levels.
In other 10BASE-T1L applications, such as those in building automation technolo- gies, APL compliance is not required. Thus, the concepts of spur and trunk are not relevant. In fact, network topologies in this technology can vary from star to line to ring or a combination of these. The transmission level may be chosen based on power limitations or noise immunity independently of where the sensor or network switch is placed. This allows more flexibility in the use of cables, as the 2.4 V p-p transmission level can be used independently of where the link is located, allowing higher tolerance for signal losses in the cable and a less strict nominal cable impedance. This will be explored in more detail in the following sections.
