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

All GS4 drives have 8 Digital inputs standard and you can add more inputs using these option cards. What do you use digital inputs for? Well, they are called “Multi-Function” inputs for a reason. If you look at parameter group 3, you can see the 8 native inputs and the 6 inputs from the optional I/O card here. And in this column, there are 50 different functions you can assign to the inputs. You can use the inputs to control multi speed or PID set points, reset or jog the drive, switch between drive settings, determine if the drive speed is controlled by the analog inputs or not, Control Fire Mode, disable all motors or just one at a time, etc. All kinds of stuff. Let’s do an example. Let’s say we want Digital input 1 to act as a forward jog. We just go to Parameter 3.03 which is digital input 1 and we tell it that he is now the forward jog by entering a 24. If I toggle digital input 1 – uh-oh - the motor doesn’t start turning – why not? Well, digital inputs almost always depend on something else being set to use them. For example, we can assign a digital input to control PID, but if PID isn’t setup in the drive, it won’t do anything – right? Same thing here, we told digital input 1 to control the forward jog, but we also have to tell the drive to use external inputs for motor control. You can do that from parameter 3.0 or 3.1 – they tell the drive what to use for control: the keypad, an external terminal, RS485 – which would be a Modbus or BACnet, or should control come from a communications card. We want to use an external digital input terminal and let’s choose the version that allows us to stop the motor from the key pad if we need to. So now if we enable digital input 1, sure enough the motor starts to ramp up. Perfect. Well, in a nutshell that’s really all there is to it, but there are a couple other things to be aware of. All of the drive and option card inputs can be read by the PLC to use for whatever it wants. But, the PLC numbers the Inputs differently, because inputs 0 and 1 for the PLC are the Forward and Reverse. Also notice that the drive starts the option card inputs at number 10, so it skips 9 and the PLC starts the next sequence every 8 inputs, so it skips 8 and 9 in its numbering of the inputs. So just remember when going back and forth between the PLC and the drive – that the inputs are numbered differently. Parameter 3.42 lets you specify if the input should default to normally open or normally closed. The mask at parameter 3.48 is where you see which inputs are being used by the drive and which are being used by the PLC. An input can only be used by the drive as a multi-function input OR the PLC as a generic input, it can’t be used by both at the same time. In this example, we see Inputs 1, 3 and 4 are being used by the PLC because there is a 1 in those locations in the mask. And notice that those correspond to PLC inputs X2, X4 and X5 because as we mentioned earlier, the input numbering in the PLC is different. I’s important to understand that if the PLC uses an input – and the PLC is not disabled - it owns the input. It doesn’t matter what function you assigned it in the drive. The PLC ALWAYS wins if it uses the input in the ladder code and the PLC is no disabled is not disabled. And I love this – Parameter 3.46 shows you which inputs are active – this is a great way to visually test signals coming into the GS4 Drive. Parameter 3.41 allows you to change the response time of the digital inputs. That’s great for debouncing switches or ignoring intermittent noise you might get on the digital inputs. There is one exception – when digital Input 6 is set to a 23 – that is, it is setup to be a high-speed counter – then it uses parameter 3.40 to adjust its filtering. Input 6 Is a special case because it’s the only input that is specifically wired for high speed counting. And the best news is, you don’t have to remember any of this. There is a chart in appendix C that looks like this that tells you at a glance everything we just did. The terminal numbers, the PLC numbering, which parameter controls which I/O, what their default values are, how to select normally open or normally closed, how to set the response time of the input, how to view all the inputs and how to make the inputs active for the PLC. There is another chart just like it for the option card digital inputs. The only difference is the option cards don’t support filtering of the response time. And of course, it depends on which option card you use, the combo card with 4 inputs or the dedicated card with 6 inputs. This graphic in the manual shows you exactly how to wire up for Syncing or Sourcing whether you are using the internal or an external supply to power your digital inputs. Click here to learn more about the GS4 drive. Click here to learn about all of AutomationDirect’s free support options, and click here to subscribe to AutomationDirect’s YouTube Channel so be notified when we publish more videos.