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Student Spotlight continued
Prototype Board vs PLC
There have been other recently-produced “emergency ventilators” using prototype controller boards like the Arduino, and it would be reasonable to wonder why the Auburn team replaced their Arduino with a PLC. Prototype boards are perfect for education and proof-of-concept: they are quick to procure, cost-effective, easy to program and modify, and ready for I/O out of the box. However, they are commonly mistaken to be suitable for all applications. For critical applications, however,
the hardware and software simply do not offer the needed reliability.
PLCs, from a hardware standpoint, are built
to withstand large variations in temperature, high-vibration, and other harsh environmental factors. As far as software goes, PLCs run real-time operating systems (RTOSs) that execute all logic and scan inputs and outputs hundreds of times per second. AutomationDirect CLICK PLCs provide cost-effectiveness and ease of configuration in addition to the robust hardware and RTOS qualities of PLCs.
Prototype boards, by comparison, are not manufactured to endure harsh environments. From
a software-standpoint, they operate primarily as cyclic execution systems, requiring received or output commands to fully complete prior to moving to the next line of logic. While there may be workarounds to reduce the risk of these systems “hanging” in
the event of an error, these factors make prototype boards unfit for use in critical systems.
Design Details
Auburn University’s RE-INVENT integrates an unmodified CPAP machine with the following elements:
• Oxygen-blending valve
• Actuated valves
• Viral filter
• Hoses
• Pressure transmitter
• AutomationDirect CLICK PLC
• AutomationDirect C-More HMI
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Student Spotlight
CPAPs RE-INVENT ed into Ventilators Using PLCs & HMIs
Break Room
The team sourced many of the COTS automation components through AutomationDirect. Excluding the CPAP machine, each RE-INVENT unit utilizes about $950 worth of parts, coming in well over the Hack- a-Vent’s constraint but still a very reasonable cost (Figure 3).
Figure 3: Excluding the CPAP machine itself, the RE-INVENT ventilator assembly is configured from less than $1,000 of commercial off-the- shelf parts.
When Chapman came on board, he quickly specified the AutomationDirect CLICK PLC
and C-More HMI as the perfect candidates for RE-INVENT, citing their ease of use and reliability. For many years he had used CLICK PLCs under harsh environmental circumstances without failure, so had no hesitation recommending their use in a life-critical application. Additionally, their ready availability, quick procurement, and reasonable cost made it an easy choice for the application’s PLC.
Chapman used the AutomationDirect free PLC software to program the control logic and the low- cost HMI software to configure the user interface.
In Chapman’s experience, the AutomationDirect products are also effective as a teaching tool because the new programmers can immediately begin creating ladder logic without user-interface distraction or an excess of prerequisites to configure.
In addition to the PLC and HMI, the Auburn
team purchased power supplies, circuit breakers, zero-cross relays, terminal blocks, DIN rail,
wire, and cables directly from AutomationDirect. AutomationDirect also provided world-class customer
Student Spotlight www.automationnotebook.com | Issue 44
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