The GSD8 Digital DC Drives can be set up as a master follower so you can synchronize two
or more motors.
This is great for blending and batching feeders; chemical pumps where maybe you need to inject
additives into waste water at some percentage rate; web systems where you need tensioning, take-up/take-off;
laminating two sheets pressed together; liquid gel forming, etc.
There are lots of applications for a master follower pair.
So let’s do a quick example.
This master is set up in Rate mode, exactly like we did in the first video of this series
and we don’t need to modify it, so I’m not going to repeat that here and just focus
this video on the follower.
Suppose we have some kind of feeder system or blending system where we need one motor
pumping at one feed rate and another motor pumping at some ratio of that rate.
The key point is no matter how fast the main feeder system is running, we want the second
system to keep up, so a constant percentage or ratio mix is maintained.
This is the wiring we did for the Rate mode demo in a previous video.
That will be our master and it requires NO changes.
To add a follower, we do an almost identical setup.
Add a motor.
Attach an encoder – or whatever sensor you are using – and wire the sensor to the drive.
The only difference is we are going to take the sensor signal from the master and wire
it to S2 on the follower.
I also wired the inhibit switch to the follower, so I can shut them both down at the same time.
That’s it for wiring.
I chose to use a 5-amp drive and a 1 horse power motor for the follower just to show
you that you CAN mix and match these things.
Of course, you would want to choose the type and size devices you need for your application.
These are the parameters we will need for the follower drive.
Let’s do a factory reset to make sure we are starting in the same place.
Hold the enter key to get into parameter mode.
Go to parameter 95.
Enter a 5 and hit enter.
Press the up arrow to confirm and we are now at the factory default state.
Ok, we want this drive to be in Follower mode, so I’ll drop into parameter entry, scroll
to parameter 10 and enter a 3 for Follower mode.
Enter to accept.
For the Display mode in parameter 12, let’s start with it in leader speed mode, which
is 3.
That will show us the MASTER’s encoder value so we know we are getting the correct sensor
signal.
Once we see that’s working, we’ll change this to show the follower speed as a ratio
of the master in percent, so we can easily dial up any ratio we want.
S2 defaults to Jog signal, so we need to change that to a 1 so the drive can use S2
as a follower signal.
Let’s go to parameter 37 and make sure it is set to the 20 pulses per revolution that
our encoder is generating.
It is … so we are good there.
Well, that’s it for parameter entry, but don’t forget .. mode changes require a power
cycle, so I’ll power down … wait a couple seconds … and then power back up.
Let’s try it.
I’ll disable the inhibit and we see the master ramp up to speed.
But the follower isn’t doing anything.
We see in the follower display that it is getting the pulses from the master so what’s
going on?
Well, we haven’t told the follower what ratio to use.
Now that we know we are getting the master's pulses, let’s go back into parameter entry
mode, go to parameter 12 and change the display to show us the percent speed that we want
the follower to match the master at by entering a 1.
And I’ll scroll to parameter zero and hit enter to get out of parameter entry mode.
Ahh, look!
The follower is being told to run at 0 percent of the master’s speed!
Let’s change that to match the master’s speed or go to 100% of the master’s speed.
There is an implied decimal point here, so we need to go to 1000.
You can see the follower motor starting to rotate as I scroll up to 100%.
It’s moving, but is it really tracking?
I’ll bring up a strobe light and dial it up to this RPM and sure enough, we see the
follower tracking the master.
Cool.
If I change the percentage, we see the follower losing track of the master.
If I go back to 100%, it locks in.
Perfect.
I’m going to go back into parameter mode one more time and change the display mode
in parameter 12 to a 2.
This will show us the real time tach value of this drive’s motor but it allows us to
flip over to the percent value and adjust that.
Scroll down to zero to exit.
OK, the master is at 1300 RPM which we see in both displays, so let’s take the follower
down to 50% of the master’s speed, and the display reverts to tach mode and we see the
follower motor is now running at 650 RPM.
Exactly what we expect.
And since it’s an even multiple, the strobe shows us both that motors are still in sync.
Cool.
And really all we did was connect the two drives via one wire and change a couple parameters
in the follower and we were up and running.
Not bad at all.
Wouldn’t it be cool if you could do this with ANY DC drive – even an analog drive
that is normally controlled with an analog speed pot and doesn’t have feedback?
Well, guess what?
The GSD8 series of DC Motor controllers has a digital speed pot that does exactly that.
It replaces the analog potentiometer with a digital one and adds a feedback path,
which means you can run the analog dc motor controller both open loop or closed loop.
And does this have to be a DC motor controller?
Nope.
You can use it with any controller that requires a voltage reference in.
Join me in the next video where we will do a quick example of how to use that digital
pot.
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