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Old March 24th, 2020, 01:33 PM   #1
Bullzi
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BACnet Protocol

Hi Everyone,

Woking on a job where I will be interacting with a heating controller that uses BACnet. I have never dealt with BACnet before so I have a couple of questions.

1. How does BACnet work? Is is a Master/Slave protocol like Modbus?
2. What is the Database structure of a BACnet controller? Tag? Address? or numeric like Modbus?
3. I plan on using the Red Lion CR3000 HMI as a converter from BACnet to EIP. How do I set up Crimson for BACnet?

Thanks for the help!!
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Old March 24th, 2020, 05:04 PM   #2
ASF
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I've used a little bit of BacNet, prosoft make some modules to interface to Ethernet/IP, and I've set a couple of them up.

From memory, they use an alpha-numeric type addressing scheme, e.g.
BI123 = Binary Input 123 - a digital input
AO456 = Analog Output 456 - an analog output
BV321 = Binary Value 321 - an internal bool
AV654 = Analog Value 654 - an internal analog value (I think all analog values are floating point, but don't quote me on it)

There are other more complicated data types, but for your purposes I don't suspect you'd need to get too far into that.
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Old March 24th, 2020, 06:41 PM   #3
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If the Red Lion has an interface to your PLC you just select that on one side and BACnet on the other side (of the type required - there are several forms of BACnet) and you map the I/O. Additionally you may have to scale and select different types of values - eg kilowatts, volts, hertz etc true and false for the BACnet people. They just extract everything from the Red Lion device. There are several types of inputs and outputs as above and there is a word type that is 16 bits as well so you can map 16 bits into a word in the PLC and the Red Lion device will bust it up into bits for the BACnet people. Just finished a job with an Anybus Modbus to BACnet converter.
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Old March 25th, 2020, 06:57 AM   #4
saultgeorge
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Hi, if it's any help, I just got through with a 2 year project with air handlers and BACnet. I worked for an integrator and we contracted a company that did all the BACnet stuff. The company we were doing the project for wanted all A-B PLC processors and I/O. The way we worked with the BACnet and the building automation system was we used a Real Time automation gateway to talk to the JACE controller, which is the BACnet hardware. It uses software called Niagra I believe. So the BAS was linked directly to the JACE, which I could see through the gateway. We just made a template for the BACnet tags in logic. The HMI was a real POS and had the ASHRAE type buttons on it, as well as the graphics. They were really bad. The BAS system had the same thing on a computer. The operator could change setpoints, override valves, settings, etc and get statuses back from the PLC. It was really cool. If you're interested I can send you a screenshot of the template we used in logic to set up the tags. (RS 5000) Hope this helps.
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Old March 26th, 2020, 11:34 AM   #5
Bullzi
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Thanks for the info everyone!! saultgeorge, I would grateful if you would share that template with me.
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Old March 26th, 2020, 01:34 PM   #6
saultgeorge
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Bullzi
OK, so here's the scoop. This is working well for us when I did a bunch of air handlers for a new office building/lab at Ford the last 2 years. I wrote all these programs from scratch, BTW. So you may think something is weird, but everyone programs differently.
The snip shows UDT's which will be as follows: Bacnet_in is AHU control and AHU setpoints, Bacnet_out is AHU alarms and AHU status. So those AHU UDT's are nested in Bacnet in and Bacnet out. Bacnet "in" means an operation from either BAS or the operator OR from the HMI will go through the BACnet software in the JACE controller and then into the gateway and into logic. BACnet "out" is reversed. A readback, for instance, from a setpoint would go the other way and show up in the HMI at the unit or the operator console at BAS. Lastly, the RTA gateway is where the real template comes in. Those gateways are like anything else, the tags have to match exactly or it won't send or receive a value and just throw an error for that point. The first few units I did in '18 I had the PLC tags in the gateway, and had a lot of problems with this--syntax, data type etc. So my boss invented this template for these last 3 units.
So the way this works is your BACnet integrator will assign points to his program. An example in the snip is Outside air temp. It comes into BACnet from the BAS. He assigned it to a point in his program, which is irrelevant to me. I then had him assign that point to BNET.AO_44, which is in the RTA Gateway UDT. He can see this. His system doesn't care what my tag name is, only what point I want it assigned to in the gateway. Now I took that gateway tag, BNET.AO_44 and used it in logic, for which now I can assign that analog value of Outside air temp anywhere in logic. So the BACnet out is going into the gateway (RTA_in.AHU_Control.Outside_Air_Temp.) and I moved it to a tag which I use in logic. Actually OAT is important for heating and cooling mode changes/permissives.
So then, an AI would be like supply air temp which comes into my PLC from a sensor in the unit to an AI card in the rack. I send that value up the "chain" as I described above in reverse to the gateway, JACE, HMI and BAS console/operator so they can see it. Hope this helps you, let me know if I can be of further confusion--I mean assistance. Stay healthy and safe.
Attached Images
File Type: png BNET_Gateway routine.PNG (74.0 KB, 8 views)
File Type: png Binary.PNG (40.2 KB, 7 views)
File Type: png UDT'S.PNG (25.8 KB, 7 views)
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