The complexity of the modern factory has brought intense demand for precision and efficiency in the machines, control systems and communications required for it to operate. The cost of error has driven more and more factories to automate as many of their processes as possible. With this push towards automation, microcontrollers (MCUs) play a key role — particularly in sensor communication networks, and equipment monitoring.

Consider sensors and transmitters throughout a factory – a typical sensor system will consist of the sensor element, a control block for processing sensor data and a communications interface (Figure 1). The microcontroller in this system is often responsible for amplifying and reading the value from the sensor element. This data is then processed and used to either take an immediate action, such as turning on a cooling system as temperature rises, or is transmitted back to a central node for overall system monitoring. This communication handled on the MCU can take several forms. It could involve wired protocols such as IO-Link or 4–20mA current loops, or could leverage a wireless transceiver to pass information throughout a factory. Even a basic system such as this presents challenges that must be addressed by microcontrollers in the system.

Figure 1: A typical industrial sensing system.

The challenges

Factory automation and process control in industrial systems bring unique sets of requirements and challenges for engineers:

• achieve more performance on a reduced power budget;

• collect more precise sensor data to make better decisions;

• operate in increasingly harsh environments;

• fit the entire design in a space-constrained location.

From a power perspective, developers are often constrained by the energy available, whether that energy comes from a battery, where replacement could mean high labor costs across thousands of sensor nodes, or operating from a current loop, where each node must consume under 3 mA of current to meet the overall specifications of the loop.

While working to minimize energy consumption, these developers are often faced with a need to capture above 16-bit resolution on sensor readings so that the system can distinguish between small changes in the environment and make the desired decisions. They also require high-performance analog for communicating on current loops. All of this is amplified by the need to operate at higher temperatures in cases such as those where sensors are located next to large motors. Finally the entire sensor node must fit within the communication wires connecting different parts of the overall automation system. These challenges are real, but the need to support multiple protocols such as IO-Link, 4–20mA and HART® creates software complexity as well (Figure 2). The MSP MCU portfolio offers chipsets to meet any and all of these challenges.
Protocol Description
4-20 mA Current Loop All components communicate on a single loop, using current to represent a value (like water level) – 4 mA represents min. value (0 meters), 20 mA represents max value (100 meters), 0 mA represents system failure.
HART Superimposes a small AC signal over the existing DC signal in a 4–20mA loop, and provides a “smart” digital interface, enables additional information (i.e., beyond just water level) to be transmitted, and allows for two-way communication in the system.
IO-Link Point-to-point digital serial communication ideal for communicating with sensors and/or actuators. Allows two-way exchange of process data, service data and events.