Digital Outputs on the GS4 Variable Frequency Drive (VFD) from AutomationDirect

All GS4 Drives come with 2 digital outputs and 2 relay outputs standard. You can add more discrete outputs or relay outputs with the optional I/O cards for a total of 8 possible outputs. The drive can use the outputs to indicate all the items in this list including: if the drive is running, if it’s at frequency, Torque status, Dynamic braking active, forward and reverse, etc … And to use it you just put the number of the function you want in the drives output terminal’s parameter. For example, let’s put the “At Frequency Set Point” – which is a 2 - in output 1 which is parameter 3.19. Now, when the drive reaches speed this LED I connected to Output 1 lights up. Perfect. That’s all there is to it, but there are some things you do need to be aware of when using the outputs on a GS4 Drive. The two built-in relay outputs are in parameters 3.17 and 3.18 and the two built in digital outputs are in parameters 3.19 and 20. The six option card outputs drive either the 2 digital outputs on the combo card or the 6 outputs on the relay card. So you get either two additional discrete outputs or 6 additional relay outputs, not both. And look at this – there are 5 Virtual outputs. Those are just additional bits the PLC can use for whatever it wants. They are used by the PLC just like regular coils, they just don’t physically drive anything. These are particularly helpful if you need to set a status bit for an external device to monitor via the comm cards, for example. All discrete outputs default to no function, but the relays default to error status and drive running status. You may have noticed earlier that when I enabled the drive this LED turned on. It is connected to Relay 2 which was still set to the default Drive running status. Parameter 3.43 lets you set the behavior of the outputs – do you want them to act as normally open or normally closed contacts? The default is normally open. Parameter 3.47 shows you graphically which outputs are active – that’s really handy when you are trying to debug your system. And parameter 3.49 shows you which outputs are used by the drive and which are used by the PLC. That’s really important to understand. If the PLC side of the drive uses an output, then that output is automatically owned by the PLC – and whatever drive related function you assigned it in the parameters is overridden. So for example, suppose we tell output 1- which is parameter 3.19 – that we want it to indicate when we have an under-voltage condition by entering a 10 into 3.19. Well, in this case, it won’t work because we see that digital output 1 – which is the 4th bit location - is in use by the PLC. It doesn’t matter if the PLC is in RUN or STOP mode, if the output is referenced in the ladder code then the drive functionality we specified for that output is overridden. Which is why parameter 3.49 is so important – you can see at a glance which outputs are owned by the PLC which means if you try to use them for a drive function – the drive function will be ignored. So be sure to keep an eye on that. The PLC numbers the outputs differently than the Drive. The good news is you don’t have to remember that because the ladder instructions show both the PLC’s designation and the Drives terminal numbers. Section 2 of the user manual has a great graphic that shows you exactly how the outputs are wired and even includes the specs for each output. If you use a digital output to drive an external relay, PLEASE do yourself a favor and add a surge absorber across the relay’s coil. Check out these videos if you want to know why it is so important to protect your digital outputs – and I’ll give you a hint – the couple bucks you spend on a surge absorber will save you a lot of time and money. Check out this handy table in Appendix C. It has everything we just covered in one easy to reference place so you don’t have to memorize any of this. The terminal numbers vs the PLC names for those terminals. Which drive parameter controls which output and what their default settings are. How to define the normally open vs normally closed state of the output. How to monitor the output status and how to tell if the PLC is controlling an output. And a complete list of all the possible drive functions you can use if the PLC is not controlling the output. There is another chart for the option card outputs which covers the two outputs on the combo card and the 6 relay outputs on that card. And one more table that covers the virtual outputs. These are only used by the PLC so you don’t see any drive functions listed here. Finally, if you remove these two screws, you can pull the I/O terminal board out so you can do your wiring where it is easier to work with outside of the drive. When done, just slide it back in and re-attach the screws. This slot 3 up here is where the optional I/O cards go. Just plug the one you need in, and screw it in place. Run your wires directly into the terminal blocks here. Click here to learn more about the GS4 Variable Frequency Drive, click here to learn about AutomationDirect’s free support options, and here to be notified when we publish new video content.