Let’s setup a WEG CFW300 drive with three digital inputs to control 8 different reference
frequencies.
Maybe you have a drill press and depending on the material that you are drilling or the
bit style you are using, you want to be able to select with a switch which spindle speed
you want without having to dial in the correct speed manually.
Well … that’s what this Multi Speed option is for.
Given 1 to three digital inputs you can select up to 8 possible predetermined frequencies.
It’s easy to do, but there are a couple things you need to be aware of when implementing
multispeed so let’s do a couple quick examples, so you can see what to watch out for.
Before we get started though, let’s reset the drive to factory default so we are all
starting in the same place.
I’ll set this up using the free WEG WPS software because it’s easier for you to
follow along.
My PC is connected to the drive via the optional USB module.
You don’t need the free software or the optional module – you can do all of this
from the drive’s built in HMI keypad.
I’ll even give you a summary list of parameters at the end, so you don’t have to remember
all of this.
I’ve already created a configuration and a resource, and I’m connected to the drive.
For this demo, we’ll operate multi speed in local mode, so I’ll search for local
and we see that the local reference frequency source is set by parameter 221 and it defaults
to being controlled by the HMI.
So, we’ll change the local reference frequency to being controlled by the multispeed function.
Now we just need to assign digital inputs to control the multispeed.
This is where it gets a little tricky.
This chart in section 7.2.3 of the user manual is your best friend because it tells you everything
you need to know.
These parameters hold the 8 possible reference frequencies that we will be able to select
from.
If I search on Multi I see the default values are these, so I’ll add those to the chart
here as a reminder.
These default values are for the 60 Hz factory reset we just did.
They will be different if you reset the drive to 50 Hz factory default.
So just be aware of that.
The key thing to note here though, is only these digital inputs can be used for bit zero.
These digital inputs can be used for bit1 and these digital inputs can only be used
for bit 2 - the most significant bit.
For our first example, let’s use these to control multi speed.
I’ll search on DI and set DI1 to multi speed, DI3 to multi-speed and DI4 to multi-speed.
Again, because they are predefined, the drive already knows which one is gonna control which bit.
That’s it, except it looks like we have a configuration error.
Hmmm .. what is going on?
Remember, whenever you get a configuration error, go to parameter 47 – it’ll give
you a pretty good idea what’s going on.
Looks like this is telling us that either parameter 224 – that’s the local mode
run stop - or 227 the Remote Mode Run/Stop, are trying to use the digital inputs we are
using for multispeed.
If we search on local – it’s not using any digital I/O except the multi-speed stuff,
we are using.
That’s ok.
So, let’s go look at remote.
Ahh ... remote is expecting digital inputs to control the forward and reverse and the
Run Stop.
There’s the issue.
We’re using DI1 for multi-speed, but remote mode is expecting it for run stop.
So let’s make the remote run stop controlled by the HMI for this demo … wait for the
change to take effect – that can take several seconds depending on how busy the drive is,
there we go, the screen just updated, AND look, the Drive no longer has a configuration
error.
Perfect.
So, if we turn all three bits off, and hit run, the drive runs at this speed.
If we enable bit 0, then the drive runs at this speed.
Turn that off and enable bit 1, we get this speed.
Enable bit 0 and 1 and we get this speed, etc.
We can now select one of 8 preset frequencies.
Cool.
And by the way, don’t forget, you can monitor the digital I/O either through this parameter
– that number appears in HEX, OR via one of the wizards.
Now, we used the default speed values in this demo which if I search on multi we can see
those here - but you can change these to any of thee to any value you want, and the minus
sign indicates direction.
Let’s change the value one to a minus 3 Hz.
Wait for the screen to update … again that can take several seconds … there it is.
Now when I flip bit 0, the motor runs in the opposite direction.
Perfect.
The WEG Drives have a secondary multi speed feature.
We set our Digital I/O’s to Multi Speed.
If instead, you had set them to this 2nd ramp multi speed, then multispeed would use the
use first set of ramp parameters to control the drive during startup and shut down, and
the second set of ramp parameters to control how the drive changes between frequencies
while the drive is running.
It’s just one more way you can refine how multi-speed operates.
Be careful, when using this feature, don’t set parameter 105 to a 1 – that will force
the second set of ramp rates at all times – which isn’t what we want here.
I used these discrete switches in this demo, so you could see which bit I was controlling.
Would you do it like this in your setup?
Probably not.
Most of the time you would use a PLC or some other kind of controller to control those
bits, perhaps even with an HMI.
Here is a summary of the parameters we used in this video.
And really all we did was tell local mode it’s frequency will be controlled by multispeed,
we setup the 8 present frequencies and we configured the three digital inputs to configure
which of those frequencies we want to use.
Click here to learn more about the WEG CFW300 variable frequency drive.
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