Smart Factories and the Challenges of the Proximity Network
3.1 Sensor / Actuator Interface
The sensor / actuator interface is the physical and logical interface between the sensor / actuator and the IIoT Edge Device. The following integration challenges have direct bearing on how this interface is chosen.
Powering the Edge Device – Wired-power devices allow for a much wider range of sensors and simpler hardware integration efforts. Battery-operated devices require tight control over sensor / actuator current draw.
Sensor / Actuator Integration- This consideration is extremely application-specific. Consider these three unique cases:
� The edge device reads an ADC value from a 4-20 mA temperature sensor. � The edge device samples a vibration sensor 1000 ' s of times per second and performs a fast Fourier transform( FFT). � The edge device must implement or at least transport a higher-order protocol such as
MODBUS.
The hardware( and resulting software) integration of the sensor often represents a significant portion of the development cost and time.
3.2 Proximity Network
There are a variety of connectivity options in the proximity network. We will focus on wired Ethernet, Wi-Fi and 802.15.4 technologies. We have seen these technologies cover various sets of integration challenges well, though there are certainly other technologies that could work in this environment.
Powering the Edge Device- If wired power is available, wired Ethernet, Wi-Fi and 802.15.4 are all viable technologies in the proximity network. The remainder of the integration challenges must be considered to make a good choice. However, if the edge devices are battery operated and the batteries need to last for a long time( measured in months or years) without replacement, then 802.15.4 is the better choice.
There are three primary power consumers on the edge device: Radio Frequency( RF) communication, the processor and the sensor / actuators. Power utilization is controlled by disabling the bulk of the power consumption in these three areas for extended periods of time. Typical battery-operated devices wake-up for a very short period of time to read a sensor, perform minimal processing and then transmit the data. Then they go into a low-power sleep mode. 802.15.4 is built for this particular low-power model due to its ability to very quickly transmit a single piece of data and then go to sleep. Wi-Fi takes time to lock onto an AP and typically runs an uncompressed Internet Protocol( IP) with additional RF overhead.
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