In the final part of the series, we discuss I/O devices in edge computing. As previously mentioned, the edge computing device gathers input from sensors. The gathered data is then sent through algorithms running on the edge computing device, and the device then gives corrective output via the output devices.
To gain context on edge computing, as well as the software and hardware components click on the links below:
- Process Automation: An Introduction to Edge Computing
- Process Automation: Edge Computing Hardware
- Process Automation: Edge Computing Software
Data acquisition from a process and corrective output
Computing devices work in the digital domain. Industrial Processes are on the other hand creating analog information. This can be temperature, pH, conductivity, etc. Sensors are used to measure this analog information, which is converted to a digital form and cached. This cached data is then fetched on the edge computing device. The edge computing device might employ multiple means of collecting the cached data from the sensor. MODBUS over RS485 or Ethernet are a couple of popular means.
Once the data from the sensors is sent over to the edge device and the algorithms running on it have calculated the corrective data, the next step is to translate the corrective data into real-world output. Output devices might include motors, valves, pumps, alarms, etc. The output from these brings about changes in the process. The change is then sensed by the sensors. The sensors, the edge device, and the output devices together form the feedback loop that controls the process.
Human Machine Interface
Human Machine Interface (HMI) is an input-output device. An HMI is used to control and monitor any software, hardware, or process. The screen on an ATM is an example of an HMI device.
In the industrial setup, you can expect an HMI to show you various process parameters like temperature, pH, conductivity, turbidity, etc. The HMI can also be used to show tank levels, and show a map of functional elements like pumps, valves, and their status.
An HMI can either be a touchscreen or a screen with various function buttons. The touchscreen or the buttons are how the operator provides input to the system for controlling it. The programmer who programs the software for the HMI and the edge device has to make sure that the information received from the process is correctly represented on the screen. The programmer also has to make sure that the input provided by the operator is registered and used to change the appropriate parameters.
Depending on what the product is intended to do, the software can be written in a way that the edge device can monitor not just a single process, but the entire plant.
On the hardware side of things, some key specifications of an HMI device are its screen size, the display panel technology, the display resolution, the aspect ratio, brightness, contrast ratio, and Ingress Protection (IP) rating amongst many others. The IP rating is especially important depending on the industrial environment in which the HMI is going to be used. The IP rating is indicative of how well a device can protect its inner electronics against the ingress of dust and water. While selecting the HMI screen you need to be cognizant of whether your edge computing device supports the display interface of the HMI and whether the HMI screen vendor provides Operating System Driver support.