Learn how to control GS Series VFDs with simple local I/O reads and writes and how to avoid dealing with ModBus using the new GSREGRD and GSREGWR instructions.
The GS Series VFDs from AutomationDirect are already pretty easy to use with a DoMore PLC. You can either connect them via multi-drop RS485 OR use the EDRV100 Ethernet to serial converter so you can talk to the drives via an Ethernet network. In both cases you would use the DoMore Modbus commands to read and write to the drives. Thatís pretty easy, but every time you want to do anything with the drive you have to go through the whole send a command, wait for the command to finish, verify the command ritual, to ensure robust drive control, right? Wouldnít it be great if you could just control the drive with some reads and writes to local memory and have the DoMore take care of all the tedious stuff for you? Weíll, guess what, thatís exactly what the Ethernet I/O does! You just enable the Ethernet I/O feature and now you control the drive as if it were simple local I/O by reading and writing to a built in GS Drive Structure. Letís take a look. Were using the same hardware we had in the quick start video: A DoMore Base, an EBC100 Slave, a Terminator Slave and the EDRV100/GS drive combo that we want to talk to in this video. Check out the Quick start video to see how to set things up, but really all you do is enable the Ethernet I/O feature here ñ by checking that check box ñ Click on Ethernet I/O master, automatically scan the network for available hardware, and select the items you want to talk to. My system is already setup, so weíll just say OK. And thatís it! My GS Drive now appears to my program as just another local device. If I look at my memory tree over here, I can see under GS eDrive a GS-Drive structure ñ thatís for the new GS Drive I just added. If I had eight drives out there, I would see 8 structures. If I want to see all themembers of that data structure I just click on this plus sign and you can see all the things you can access on that GS Drive. You can set the speed of the drive, run the drive, you can set the direction of the drive, you can use some of these block transfers, watch the output current, the output frequency, all kinds of things. Well, accessing that is as simple as bringing up a dataview, and typing it in down here. The name of that guy was dollar sign GS 120, and suppose I want to monitor the output frequency. Well, there it is. Suppose I want to be able to run and stop the drive. Well, same thing. I get my structure, dot, RunCommand. Suppose I want to set the speed of the drive. Well, same thing. GS Drive, dot, and if I want to scan down the list I can do that, and thereís my speed reference right there. What if I want to set the direction of the drive? Same thing: GS Drive, dot, Direction. Well, letís try it. Letís go ahead and put the PLC in RUN mode. Iím gonna set my new speed to 50 Hz. Thereís an implied decimal, so I need to put 500 in there. And I want the drive to start running. So I just put a 1 here and write it out and sure enough, I see my output frequency slowly ramping up to 50 Hz Ö I have a long acceleration time setup right now so you can see this ramp up. If I put a zero I here, that says stop the drive, and sure enough the drive ramps down to zero. So think about it Ö weíre actually controlling a remote drive via local reads and writes to the elements of this data structure, which we can also see in our memory tree up here. The DoMore takes those values and does all the cumbersome Modbus stuff in the background for us ñ how cool is that? Iím doing this via the Dataview just to show you all of this stuff is sitting there ready for your ladder program to use however it wants. By the way, side note here ñ if you donít see the GS Drive structure under the memory category in yur tree over here? That means you have it sorted differently than I do. If you click the button here you can sort the memory lots of different ways ñ Iím using this method right here. If you pick one of these other ones, the GS Drive structure is still there, But you may have to dig a little deeper to find it. Now one thing to keep in mind is this structure right here only has the commands that you commonly need quick access to. Like RUN, STOP, Setting the frequency, monitoring the frequency, all those things. Well, what if we want to change a parameter that isnít in this data structure like the acceleration time for example? Normally we would do a mod bus write or just enter it directly into the drive via the front panel buttons right? And since we usually set lots of parameters just to ensure everything is exactly the way we want it, that equals lots of Modbus reads and writes and/or lots of manual entries. Wouldnít it be great if you could do you drive initialization with just one command? Well, guess what, Ethernet I/O has dedicated GS Drive commands that do exactly that. For simple example letís just setup the basic drive parameters for this drive. Well, thatís easy. Come over here, and I want the GS register write command. If I double click on row 1 here, Look at this ñ hereís a listing of all the possible drive commands you might want to use. Itís a great handy reference, but it also helps fill in the blanks for you. So, weíre going to do these parameters right here. The nameplate voltage ñ if I click on that, look what happens. It tells me the range of possible values for that parameter, a description of the parameter, a place to put my data, which I want that to be 230 volts, and what parameter thatís going to go in. There are no implied decimal places and the default value for this is 240. Awesome. Letís do another parameter. Double Click on the row. I want to do the motor base frequency. Well, I can see thatís 50, 60 or 400 Hz. I know I want mine to be 60 hz. Thatís going to go into parameter 2, the motor base frequency. There are no implied decimal places ñ thatís good. And my default value is 60. Great. Letís do another one. Letís do the amps factor this time. I can see the rated amps can go from .3 to 1.0. I see the name of the parameter. But look here, the implied decimal palces ñ thereís one implied decimal place. So if I want to set this to 1.0, that means I need to put a 10 here. So how cool is that? All the information you need to correctly set a drive parameter is right here in front of you. And if you are still not sure, look at this, there are two buttons here that will take you directly to the specs or the GS drive manual. I can pop up the manual directly from the Automation Direct website, Look up the AC drive parameters, and find out everything I want to know. Keep in mind ñ thatís a direct link to the AutomationDirect website. So these only work if you have access to the internet. But regardless, how easy is this? All the parameters are right in front of you. Just click on the one you want, fill in the blanks and say OK. And I can keep on going. You can add up to 50 parameters in a single instruction. The instruction will execute all of those parameters, take care of all of the modbus reads and writes for you, and when itís done, it will set a bit which Iím using C0 for. On error it will set a different bit - which my personal preference is C99 ñ and I say OK. Well, thatís it ñ in one instruction I can configure my Drive. And look at this, becasue this instruction is edge triggered, I donít even really need a contact here, right? The first time the program runs, this will see the rising edge. It will execute that and it will never execute it again. Or I could put a contact here and say only do this on first scan. Or I could even drop this into an initialization routine that has a bunch of these for all of my different drives. Lots of things I could do, but it is all setup to make it easy for you. The main thing is, you can do your drive configuration with one line of ladder code and then operate the drive doing local reads and writes to this data structure. No modbus reads or writes anywhere. How about that? Well, that should be enough to get you started with using GS Drives via Ethernet IO on the DoMore. Be sure to check out the other videos in this series for more tips on using the DoMore PLC. And donít forget ñ Automation Directs tech support is always FREE and you will talk to a real live person here in the US within minutes. Got a question? You can call, e-mail, or even do on-line chat during regular business hours. Whatever you prefer. Spend LESS. Do MORE. From Automation Direct.