Rate mode allows you to control a dc motor using engineering units like rpm, gallons per minute, inches per second, etc. And the Ironhorse Digital DC Drive from AutomationDirect makes it super easy to do. Join us in this brief tutorial where we walk you through how to setup up and use Rate Mode in a GSD8 Ditigital DC Motor Drive.
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Let’s do a quick example using a GSD8 Digital DC Drive in Rate mode. I connected this digital DC drive to this motor. I then mounted this encoder to the end of the shaft. Beware that you may have to enlarge the hole in the fan shroud to do this. I then wired the encoder back to the drive and added a jog and inhibit switch. This encoder comes with 3 pulse rate discs for 1, 10 and 20 pulses per revolution. I’m using the #40 disc since that’s what comes pre-installed and is what you will want to use most of the time to get the most resolution and accuracy. In fact, the only time you would use the others is for very high seed applications where the pulse rate was too fast for the drive to handle them. My motor can only do 2000 RPM and the encoder has 20 pulses per revolution so that’s a max pulse rate of 40,000 pulses per minute, which is way under the drive's max input pulse rate of 600,000 PPM. Now beware the smaller 5 amp drives can only do 50,000 pulses per minute, but it is still better than the 40,000 PPM we need so we are good no matter which drive we use. This drive has over 100 parameters we can set. The good news is, for this simple demo we don’t need to change any – the factory defaults will work just fine. So, before we do anything, let’s reset the drive to factory default to make sure we are all on the same page. Hold down the ENTER key for 3 seconds – or until the Parameter LED lights up. Scroll to parameter 95 and press enter. The Value LED lights up to tell us we are changing a value. Change it to a 5 and press ENTER. The display tells us to press the up button to confirm and the down button to exit. I’ll press the up button and we are now factory fresh. By the way, this parameter entry method is exactly the same for the 5-amp drives but they don’t have the LEDs to tell you what mode you are in. Instead, you’ll see a P for parameter entry and blinking dots for value entry. Also beware that the 5-amp model parameter numbers can be different, so don’t assume the parameter numbers I am using on this 10-amp model drive will be the same for the 5-amp drives Some are, some aren’t. I’ll put the 5-amp model parameter number in brackets to remind you. Ok, let’s scroll up to ... how about … 360 RPM. I’ll grab my hand-held tach and sure enough we are right at 360 RPM. Perfect. The JOG speed defaults to 1000. So if we enable JOG, sure enough the motor goes immediately to 1000 RPM. Note that it does that immediately. It doesn’t wait for the acceleration or deceleration times. I’ll release the JOG and it resumes the speed we had before. OK, well, it’s great that it worked right out of the box, but we didn’t actually learn anything about how to configure the drive. So, let’s mess with some of the parameters so we can get a better feel for how this GSD8 Digital DC Drive works. Do you want the drive to automatically run when the power is applied or do you want to manually ramp it up to speed like we just did? You actually have three options via parameter 16. Always start at zero RPM. Always use whatever is in parameter 17. Or use the last entered value. The drive defaults to use the last entered value, so if I power down, give it a second, and bring it back up, sure enough it picked up right were we left off. Let’s change that to use the value in parameter 17. I’ll hold the enter button down for 3 seconds – the parameter LED lights up telling us we are in parameter mode. Scroll up to parameter 16 and hit enter. Let’s change it to use whatever we put in parameter 17, which according to the user manual is a 2. Enter to accept. Scroll up to 17, press enter, and let’s have the drive always start at 1000 RPM. Enter to accept. We don’t have to exit the parameter settings – as soon as we hit enter to accept the value, it was done. We are currently at 360 RPM, so if I power down the drive, give it a second or two, and then bring it back up again, it goes directly to 1000 RPM. Exactly what we asked for. Ok, we got our rate set, how about the acceleration and deceleration? Those are in parameters 23 and 24. Again, hold down the enter button for 3 seconds. Scroll to parameter 23. Hit enter. This is in engineering units per second, which for us is RPM. The 9999 says to ramp up as fast as possible. We are running the motor at 1000 RPM, so if we say we want to accelerate at a rate of 100 RPM per second, it should take 10 seconds to ramp up to speed, right? Enter to accept that. I’ll power down, give it a second, and power back up. Briefly pressing the enter button shows you the current tach value while the tach LED is lit. I’ll press it a couple more times and sure enough it takes 10 seconds to ramp up to speed. Pressing enter over and over to see the actual motor RPM is a pain. Can we tell the display to show that all the time? Sure! The number we see in the display by default is the target speed. Let’s change that to the actual speed so we don’t have to press the enter key to see the tach. Hold the enter key for three seconds. Scroll to parameter 12. Press Enter – we see we are now in value entry mode. Change that to a 2. Notice that you can also display the master’s RPM if this drive is a follower – that’s great for debugging master follower configurations because you can see if the follower is getting pulses from the master. Ok. This time lets scroll to parameter zero and hit enter to get out of parameter entry mode. Now if I inhibit the motor and wait for it to stop, then remove the inhibit, sure enough, our display is now showing us the actual speed of the motor. What if instead of an encoder, you have some other pickup sensor generating the feedback pulses coming back into the drive? Maybe you have a flow meter that sends out pulses representing gallons per minute or a gear tooth sensor counting the number of teeth passing by. You can use any sensor you want as long as it is generating a digital waveform between zero and 5 to 24 volts DC. Just enter that sensors PPR in parameter 32. One thing to be careful of. The 10-amp drive defaults to 20 PPR which is convenient because that’s what the default for the GSD8 encoders is. But, the 5-amp drives default to 1 PPR, so you may have to change that if you use one of the GSD8 encoders. By the way, I love that the drive has a convenient 5-volt output for me to use with my sensors. There’s lots of parameters for you to use to customize the drive for your application so now that you know how, go experiment with them! And, there are a bunch of optional modules and other units you can use to extend the capabilities of these drives. 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