Wiring the Factory of the Future: Passive or Active?

The Internet of Things (IoT) is bringing smarter production processes to the factory floor and simultaneously driving data volume and diversity up -- quickly. While automation networks have historically employed passive wiring in the field, leveraging IoT to improve manufacturing automation is critical to be competitive in today's global market and demands a more agile wiring policy: active wiring.

Considered the fourth industrial revolution, the desire for everything to be connected has blurred the boundaries between digital and physical in industrial settings. Interconnected systems are supporting activities across the entire supply chain and require customizable solutions for a diverse range of markets.

Understanding the nuances of your wiring options and choosing an optimal solution that caters to your network needs require a careful examination of the particular application requirements.

Passive Wiring: Where It Works and Why

Passive wiring is formed when every sensor and actuator is connected directly to the PLC without fieldbus. Discrete wiring, or hardwiring, is a form of passive wiring that does not use connectors. Rather, wire-and-conduit or cable is connected from the sensors and actuators to the PLC. Passive wiring with connectors has some advantages over hardwiring, specifically in terms of reduced installation and repair times.

There are two approaches to passive wiring. With traditional hardwiring, also known as the central variant method, the sensors and actuators can be connected directly to the control system by separate cables and are controlled by a programmable logic controller. Running and terminating the wires is very labor intensive, and the factory floor can be a challenging environment to work in. Connectors can be used to streamline the process so that the cables can simply be plugged in, and engineers can build the system in a temperature-controlled workshop.

Passive input/output (I/O) modules are another approach, where sensors and actuators are connected decentrally by means of I/O modules and common power lines and thus make installation a little easier. Digital or analog signals can be transmitted and read in both cases. Cables can be pre-assembled with standardized M12 or M8 connectors, so there is no longer a need to remove insulation from cable ends or attach ferrules.

The central variant method is time- and cost-intensive for users and poses the risk of wiring errors because terminal blocks and cable glands have to be installed.

The biggest limitation of passive wiring is that as a system gets larger, the wiring becomes exponentially complicated. A large system can have many cables connected to the cabinet, making it very time intensive to install and therefore expensive. For small systems, passive wiring is generally effective, and deciding between the two types comes down to evaluating the cost of active modules versus installation time. If the goal is to take advantage of higher technology devices and IoT, active wiring is the best approach to take.

Active Wiring: Why It Makes Sense

IoT makes passive wiring all but obsolete. Instead, high-speed bidirectional data communication is required, allowing information, such as status messages on the contamination level of sensors and actuators, their operating temperature, and the number of switching cycles, to be transmitted and evaluated.

Any system that communicates with the sensors and actuators with some type of digital communication method is considered active wiring. This includes (but is not limited to) DeviceNet, ProfiBus, CanOpen, ASi, ModBus, and even old serial communication schemes. Active wiring delivers sensors with more capabilities; these sensors can monitor themselves, store data, and alert you of possible failure points.

There are two approaches to active wiring: stand-alone modules, where each module has an Ethernet connection and can support up to 16 inputs or outputs, and a distributed system, where a LioN-Link system can be connected to Ethernet with only one module and transfer digital information over links further into the system. This allows you to create a standard product and customize the bus coupler according to customer needs.