Hobbyist Platforms for Powerful Edge Controllers - but what Control Language?

George Thomas, President, Contemporary Controls

I have been asked to express my opinion on the above subject but having once said that you would never see an IBM PC on the plant floor I need to be careful as to what I say.  I have also learned over the years never to discount the impact of a computer hobbyist movement such as we are experiencing with the Raspberry Pi.  This $35 platform certainly has educational appeal and will gain acceptance in other industries including the HVAC industry – possibly as an edge controller.  Its price is far lower than the cost of a single software license demanded by HVAC suppliers.  As a device manufacturer, we are sometimes challenged as to why our products cost more than $35?  So the Raspberry Pi has created a hardware-cost benchmark as well.
 
I feel platforms such as the Raspberry Pi and BeagleBone are best used as benchmarking platforms facilitating product design by allowing your software engineers the opportunity to begin development before hardware design is completed.  You can also verify the intended performance of the proposed design on one of these platforms to ensure design goals will be met.  I agree that if you want to use one of these platforms in your final design, it would be cheaper to purchase the assembly versus using their BOM and making it yourself.  If your product is to be a head-end supervisor, gateway or router you could probably use one of these platforms.  If it is to be a field controller I question the decision.  Here are some of the challenges:

• There is either limited or no analog I/O provisions with these platforms so this needs to be extended from the platform.
  

• You still need to deal with field signals such as 0-10 VDC and 4-20 mA so signal conditioning is needed.
  

• The HVAC industry still relies upon serial protocols such as Modbus RTU and BACnet MS/TP both using the EIA-485 physical layer so properly conditioned serial ports are needed.
  

• 24 VAC input power is expected so you need a power supply design and not just a wall wart.
  

• You need a panel-mounted or DIN-rail mounted enclosure to house your product.
  

• Can your application tolerate the 30 second boot-up time of Linux?
  

• Finally, you need regulatory compliance for your product including EMC compliance and UL safety compliance.  Can you maintain compliance with the frequent platform revisions that are out of your control?

[an error occurred while processing this directive]I am not saying it cannot be done – some HVAC suppliers are doing it now – I am just pointing out the issues if the intent is to make a powerful edge controller.
 
This concept of having a much more powerful edge controller because hardware costs are dropping – and indeed they are – assumes that software costs are dropping as well.  I am not sure that this is the case unless you want to do control using Python scripts in your Linux platform.  An open building automation protocol such as BACnet exists but proprietary control languages and proprietary programming tools remain common in the industry.  The edge controller needs to do control so where is this no-cost, open control language that will be used in this new powerful low-cost edge controller?  In BASSG’s EAC controller there is an answer and that is Sedona Framework which is open, freely-available without license, with a freely-available tool called the Sedona Application Editor (SAE) that is available from Contemporary Controls’ website https://www.ccontrols.com/basautomation/sae.htm.  Sedona has the same drag-and-drop look-and-feel as Niagara and a Sedona Virtual Machine (SVM) can be made to run on any hardware platform including Raspberry Pi.  To prove the point that hobbyist platforms are useful as benchmark platforms, Contemporary Controls has created SVMs and custom I/O kits for the GrovePi and the PiFace.  So if you want to benchmark Sedona’s performance on a close to one Gig platform you can contact us on how to install either SVM.  You can also learn more about Sedona at https://www.ccontrols.com/tech/sedona.htm.  Our position is that that Sedona Framework represents the best opportunity for creating a truly open controller that all can use.  Even powerful edge controllers can use it.