For sensor and actuator applications, A-coded M12 circular connectors are preferred. Whether it is transmitting signals, data or power, the M12 connector has become an indispensable interface as an interface for device networking.
The M12 circular connector has become the universal standard for industrial plug connections. Many manufacturers offer this compact, standardized interface, which makes it attractive for industrial applications ranging from signal and data transmission to power transmission. The robust, mechanically and environmentally resistant M12 connector is named for its locking thread with a nominal diameter of 12 mm. The wide range of applications of the M12 connectors is reflected in the number of mechanical codings (unique application-specific mechanical housing contours) that comply with the standards for the respective application area.
Dust and liquids will not damage the M12-A circular connectors from Würth Elektronik eiSos. The connectors are IP67 and IP68 rated for use in harsh environments.
The A-code mechanical shape is the origin of all M12 codes; all other mechanical locking systems are developed from it, which is why there are different codes (A, D, L, X, S, etc.), each with Different number of contacts available. Although M12 interfaces can have from 2 to 17 contacts, in practice 3, 4, 5, 8 or 12 pins are most commonly used. The number of pins depends on various requirements. For example, sensor and power applications require 3 and 4 pins, while Profinet and Ethernet applications require 4 and 8 pins, and Fieldbus, CAN Bus, and DeviceNet typically require 4 and 5 pins. 12 pins are required for complex signaling. Table 1 outlines the protocols and connector pin count required at the physical level.
Table 1: Physical layer overview of M12-A encoding. Würth Elektronik offers M12-A coded circular connectors with 4, 5 or 8 pins.
Sophisticated connection system
M12-A represents the signal with DC power option and is particularly suitable for fieldbus applications in industrial automation. The WR-CIRCM12 series features screw lock housings and cable assemblies, available in 4, 5 or 8 pin. Areas of application include industrial environments, especially automation and robotics, as well as the fields of renewable energy, communication technology and mechanical engineering. Additionally, panel and field-wireable versions of the M12 connector are cULus certified (UL2238). All M12 connectors offer a minimum protection of IP67 or IP68 against dust, dirt and water ingress.
Ensure reliable Ethernet communications
Sensor and actuator applications rely on fast, error-free transmission of digital signals via cables. The basis is Ethernet Twisted Pair (EOTP), which is considered one of the most important physical layers of Ethernet. It is the basis for the EtherCAT, EtherNet/IP, Profinet, CC-Link IE, Powerlink, Sercos III and Modbus TCP protocols.
Although M12A is not the original connector for which the EOTP interface was developed, the connector can still be used in various ways. For example, the 8-pin M12 circular connector can be used as a replacement for RJ45 in ANSI/TIA-568 Category 3 cabling systems for the 10BASE-T Ethernet interface at 10 Mb/s. Cat 3 cable consists of four twisted pairs with a typical differential impedance of 100 ohms. Figure 1 shows the recommended assignment when wiring RJ45 (8P8C modular plug) using M12 A-coded circular connectors. On the other hand, when wiring an M12 A-coded circular connector to an M12 A-coded circular connector, it is recommended to use the pin assignment shown in Figure 2.
This pin assignment minimizes delay skew between the same pair of contacts. This wiring is a widely used configuration for A-coded M12 EOTP wiring. Although 10BASE-T uses only two pairs for signaling, it is not recommended to have only two pairs in the cable or to use four-pole A-coded circular connectors, as this may cause confusion with other widely used applications. On the other hand, it is recommended to use D-coded connectors for two pairs of EOTP cabling M12. Other Fast Ethernet variants are also possible, notably 100Base-T for applications up to 100 Mb/s that require D-coded circular connectors with two pairs of cables, or higher for Base-T for data rates up to 10 Gb/s. However, for the latter, an X-coded circular connector with four pairs of cables is required.
Is it possible to alternately implement a higher clocked EOTP standard using M12-A encoding without compromising speed and signal integrity? For the 100 Mbit/s EOTP standard, an interface with an A-coded circular connector can be created with the same pin assignment as for 10-BASE-T. Signal integrity must be considered when designing such interfaces. The entire cable assembly, including connectors, must comply with ANSI/TIA-568 standards. Each plug/socket pair and the cable itself has a loss and crosstalk budget that cannot be exceeded. It is recommended to test the S-parameters of this interface, mainly depending on the cable category and cable length. Even at data rates up to 10 Gb/s, it is possible to create M12 circles with A coding by implementing the same pin assignments and applying the same signal integrity considerations as 10-BASE-T and 100-BASE-T connector interface. The cable length for this type of interface is usually much shorter.
Wide range of applications
This is by no means the end of the range of applications for the rugged M12-A circular connector. For example, the IO-Link communication system can be used to elegantly connect smart sensors and actuators to automation systems in accordance with IEC 61131-9 - using a 5-pin A-coded M12 circular connector connected to a three-core or five-core 20 meter cable . Connections on three-wire cables are called "Class A" and connections to five-wire cables are called "Class B." Device connections can be fixed cables or 4- or 5-pin M12 A-coded, depending on the required cross-compatibility.
The M12-A can also handle USB connections. With USB version 2.0, it can be used as both a power source and a high-speed data bus. M12-A circular connectors are suitable for making rugged USB cable assemblies. In the cable assembly for USB 2.0, you must consider two power connections for V-bus and GND, as well as a twisted pair with a differential impedance of 90 ohms for the USB signal. If the connection is a mini or micro-USB plug, the ID pins can be connected like this to a five-pin M12 A-coded round plug. The connector is shielded with the cable's shield braid. USB cable lengths are typically between 1 m and 3 m.
M12 connection technology is ideally suited as an intermediate link in industrial bus systems, in particular CANbus, RS-485, Profibus and the physical layers RS-422, RS-423 and RS-232. Although CANbus was originally designed for use with small D-SUB connectors, the five-pin M12-A coded circular connector is the common interface for CANbus. Only the CAN_H and CAN_L signal pairs connected to pins 4 and 5 are required. In this configuration, the device can provide power. Twisted wire pairs with a nominal impedance of 120 ohms are used for electrical transmission.
The RS-485 physical layer is commonly used for the industrial protocols Modbus, OSDP, SSCP, SCSI-2, SCSI-3, Profibus, Nanoréseau, DMX 512 and AES 3. Figure 3 shows the typical RS-485 pinout for a 5-pole A-coded cable. Alternatively, four-core shielded cable can be used. The wiring depends heavily on the power required, but always include at least symmetrical TxD/RxD pairs in positions 2 and 4 to minimize latency.
Profibus supports the decentralized concept. The fact that Profibus can be adapted to different applications using modular principles also makes this technology attractive in production automation and process industries. M12 connection technology is essential here. The A-coded variant is used for power supplies, while the B-coded circular connector is dedicated to Profibus signal transmission (Figure 4).
Other industrial bus systems using M12-A circular connectors include RS-411, RS-423 and RS-232. 8-pin, 5-pin and 4-pin connectors are suitable for this purpose. Wiring depends primarily on the required signals, power, and required grounding.