In part I we configured a Variable Frequency Drive - or VFD – so we could control it
over the network.
There may be installs where you want to do configuration and status over the network,
but prefer to do the actual drive control via external inputs.
How do you do that?
It’s easy.
Just go up here to the hardware configuration, select the VFD, and go to the Digital Tab.
Parameter 3.00 selects the source of control: a zero says use the digital keypad on the
drive, 1 and 2 say use the external inputs on the drive which you can control with manual
switches or even digital I/O from the controller if you want to, and 3 and 4 say to take all
commands from the network like we have been doing.
The STOP in here is referring to the stop button on the key pad – you can enable or
disable the keypad stop button.
If you select an external source, let’s say number 1 right here, which says use the
external source with the STOP button on the keypad enabled.
Now you have to tell it how to configure the IO’s.
Do that with parameter 3.01.
Do we want separate FWD and REV control or do we want a RUN switch with a separate switch
that controls forward and reverse?
Or do we want a RUN switch with a Forward/Reverse switch with a stop switch.
Let’s select number 1: Forward and reverse on two separate switches.
That’s all there is to manually controlling the GS Series Motor drive.
Now you can configure and monitor the drive over the network, but control it via external
inputs.
And of course, if you are controlling via external inputs you no longer need your GS
Drive Write because you are not controlling it from the network.
The nice thing about controlling the drive over the network is you only have two possible
failure points: the network connection between the controller and the GS-EDRIVE and the 485
connection between the GS-EDRIVE and the VFD – and the Productivity3000 makes it easy
to monitor, diagnose and gracefully control the motor shutdown should either of them fail.
How do you monitor the health of the connection with discrete wiring?
You can’t until the failure actually occurs.
With the network connection, that link can be constantly monitored so you know if there
is an issue before it is needed!
Here’s how.
One way is to simply monitor the status bits in each GS Read and Write instruction.
For example, if you setup a TAG to monitor the timeout status right here, and you get
a time out error, you can react accordingly in your ladder code.
The other method is to use the Communications Heartbeat.
To get this setup you have to configure the drive by setting parameters 9.03 to determine
how the drive will react, 9.04 to enable the feature and 9.05 to set the time out.
If we go over here and look at our hardware configuration, you will notice that parameter
set 9 – 6, 7, 8 .. Doesn’t exist.
You actually have to do that on the drive itself.
You can’t do it from the configuration menu here.
So again, setup parameters nine oh 3, 4 and 5 to determine how the drive will react in
the event of a timeout.
Next, you need to make sure your GS_WRITE or GS_READ are setup with a polling time that
is faster than the timeout you just set in parameter 9.05.
It’s this poling that the drive is looking for.
If it doesn’t see this within that timeout that you set in parameter 9.05, then it will
react accordingly.
Finally, you want to use a GS_READ to monitor parameter P22.01 right here.
Define a TAG for that and watch that in your ladder code and that will tell you if the
link between the GS_EDRIVE and the VFD is solid or not.
By using these features you can assure yourself of a solid robust install that will tell you
when there is a problem and help you diagnose it.
In the previous video we set the RUN and JOG commands to constants.
Fifty Five hertz and 10 hertz.
You can also use tags here.
I’ve created a TAG called RUN Frequency – let me put that in here.
So now, in my ladder code, if I change the value of RUN Frequency and this instruction
is enabled via the auto run then the drive will react accordingly on the very next polling
cycle.
It will ramp up or down to the new frequency per the ramp rate defined in my configuration.
These Mode tables that you see in the GS Drive Read and Write instructions give you a convenient
place to change GS Drive parameters on the fly.
If you enable Run Mode Data, then any parameter that is defined anywhere in this run mode
table, with either a TAG or a constant over here, will be written to the drive.
Parameters that are not defined will not be written.
This is great because it means you can update just a few parameters anytime you want without
having to send the whole table.
Note that this is an edge triggered thing, so only one set gets sent each time this rung
is turned on.
Note that the RUN mode table only has parameters that can be used while the motor is running
and the stop mode table only has parameters that can be used while the motor is stopped.
This makes things easy for you – no more guessing.
You set the rate at which drives get updates while a GS Drive Read or Write is active here.
This Polling Offset allows you to space out communications to different drives to help
improve performance and minimize congestion on the network.
For example, suppose you have 5 drives and are polling them every 100ms, consider having
the first drive delay at 0, the next one at 20ms, the next one at 40ms, 60ms and 80ms.
That way they are evenly spaced out and it will help reduce congestion of your network
traffic.
Well, we hope you find the tid-bits in this video helpful as you use VFD’s with the
Productivity3000.
As you can see the Productivity3000 is setup to help make your job easy.
Be sure to check out the other videos in this series for more ways to get up and running
quickly with this controller.
And as always, please send us any comments you may have, we appreciate the feedback.
Performance plus Value … That’s Productivity.
From AutomationDirect.