BACnet: How to Setup and Use on the GS4 Variable Frequency Drive (VFD)

GS4 Drives have BACnet built-in. That’s right – there is no extra charge for BACnet. And it’s so easy. You just go to parameter 9.86 and switch the RS485 com port to BACnet mode instead of Modbus mode. You will want to make sure the BACnet address and Device ID’s are unique on your BACnet network. Let’s change our ID from the default 10 to 37 and the address to 99 just so it’s obvious we found THIS device. Make sure the baud rate is what you need. Our USB to 485 converter we’ll be using is set to 38.4 K Baud, so this is correct. The com port parameters default to N-8-1, but you can change that in parameter 9.02 if you need to. And of course to control and monitor the drive via BACnet, we need to make sure parameter 3.0 is set to accept commands via RS485, parameter 4.0 is set to accept frequency values via RS485, and the drive is in Remote Mode. Great! Now that we’ve configured the drive for BACnet, and configured it for our network, any BACnet controller can now talk to our device. Let’s do an example. I’ll plug my USB to RS485 converter into my PC – this is the one I’m using – and plug the other end of the cable into this drive we just configured for BACnet. I don’t have a master BACnet controller handy, but there are lots of free apps out there on the internet that act like a master controller and allow you to test your BACnet system. Pick whichever one you like. For this video, we’ll use this one. Please don’t call AutomationDirect’s tech support about this app – it’s not an AutomationDirect product so they couldn’t support it even if they wanted to. When you launch this app you get a blank screen. First we have to tell it which transport protocol we are going to use. So right click and add a device. The GS4 drive uses the MS/TP passing transport protocol. I see in my windows device manager that my USB to 485 converter is on com port 11, so that goes here. The baud rate is exactly what we want. And, we’ll have it start at address 0 and search for devices through address 127 – remember – we just set ours to address 99, ID 37 a minute ago - right? Click ADD and the app automatically searches for all possible devices on this BACnet network and sure enough it finds our device at address 37, ID 99. Perfect. If we click on our device, this app automatically polls the device for all available BACnet objects defined on the device. Here are the analog value objects and here are the binary value objects. I can right click on the device and ask the app to query each object and ask it for it name. And just like that, we have all of the objects names. If I click on one of the analog value objects, then over here I can see everything there is to know about that object. Let’s click on one of the discrete objects. Again, there’s everything we need to know about that object. Analog Value 1 sets the drives frequency so let’s change that to 45 hz. Binary Value 7 enables the drive, so we’ll set that to a 1. And Binary Value 0 is the run command and sure enough the drive ramps up to speed. Binary Value 1 is the direction, so entering a 1 reverses the direction of the motor … and setting it back to a 0 changes it back to the forward direction. Analog Value 31 displays the current. frequency of the drive, and sure enough we see it is running at 45 Hz Well, that’s about it. We now have a quick way to verify BACnet. Chapter 5 of the GS4 User Manual has everything you need to know to connect a GS4 drive to your BACnet system. One side note: We said that the GS4 Drive supports the MS/TP protocol. – that’s Master-Slave/Token Passing over the RS-485 network. All that means is you have a bunch of BACnet controllers – or Master Devices and a bunch of slave devices on your RS-484 network. The lowest address master queries any devices he wants to talk to. When he is done he passes control to the next highest addressed master. When that one is done, he passes control to the next master. Etc. Only masters can initiate conversations on the network and only the currently active master – or the one with the “token” – can speak. Slave Devices can only respond to requests. They can’t generate them. The GS4 Drive is a slave on the BACnet MS/TP network. Click here to learn more about GS4 Drives. Click here to learn about AutomationDirect’s free support and click here to be notified when we publish new videos.