plc controlling a vfd

Hi,
I've just been give a task of controlling a bul. 160 ssc controller with a AB plc/5. I've never done anything like this before. I need to ramp the motor up based on the encoder output the higher the encoder count the higher the speed of the motor and vice versa.I will be using an analog card to give the motor a 4-20 ma signal.My question is how can I control the output signal to the motor and what kind of command set should I use? and where could I find a sample program to control a vfd? I have used a Mitsubishi plc FX1S-14-MT and use the high speed pulse output to control a servo drive, but I have never used an AB plc to do motion control. Any help would be very much appreciated.
Thanxs in advance
Lab

Im not an AB user but this is not as daunting as it may seem. However your approch will greatly depend on your spicific application needs, and what your drive can do.

Basicly (very basicly) you select a target speed and increment or decrement your output value to the analog unit until your encoder speed value matches the target speed value. How much to increase the analog output over how much time will depend on your application and the type (shape) output you want..depending on the application...

So...what's the application??

Thanxs for your reply elevmike,
My application is just a test stand for my self, I'm just trying to learn how to control motion via a plc.You refer to setting the increment and decrement values, is that the PTO command? or is there another?
Thanxs in advance
Lab

lab,

I'm not familliar with the instruction set for AB PLCs. By incrementing and decrementing I maybe should have stated increasing and decreasing the Drive Refrence aka analog output value. How you do that on what you want your waveform to look like. Such as a porabla, or trapizoid etc.. This is an intresting exercise but most drives these days are smarter, and will do this on their own via a drive paramater setup. The last time I controlled a drive with an analog referance generated by a PLC was more then 10 years ago..

The encoder will use a high speed counter, naturally. What you "can" do is take the encoder counts and scale them to match the 4-20ma output...depending on resolution this could be 4.000 to 20.000

I am not sure about you explanation on the encoder...the encoder can not run faster than the motor/drive. What you have to do is start the drive to ramp to a preset speed which should allow the encoder counts to equal the 4ma analog output, then you can ramp up using time or...whatever till you get to your desired speed.

You will need to look at SCP, SCL, HSC.

I am not an AB programmer, but this is how I would have done it , I use a high speed counter and count pulses from the rotery encoder, its in RPM,(do some search on this forum, if you wanna learn how to get RPM from incremental encoder), take the value of RPM and make some math , then send the value to the analog output.


for more help, you need to give more details of what are you exactly trying to achieve..


regards.

I don't know if you already solve your problem but here is a suggestion; my understanding is that the vfd is a variable frecuency drive(http://www.joliettech.com/what_is_a_variable_frequency_drive.htm) and I'm not sure if you want to make the vfd by software; there's a lot of brands out there that already do it!!! so you don't have to worry about to make the ramps, you just have to worry to start and stop the vfd. You have to program the VFD to make the ramps that you want, so you just need to program a plc output to start and stop the vfd; I already did this using a micrologix 1500 and the vfd from altivar ATV58 D54N4 (http://www.schneider-electric.ca/www/en/products/acdrives/html/atv58.htm), my application was to control a motor working at 440 VAC, 60hp so that's why we choose this vfd but it would depend from your application. Hope this give you an idea. Regards.

I don't know if you already solve your problem but here is a suggestion; my understanding is that the vfd is a variable frecuency drive(http://www.joliettech.com/what_is_a...uency_drive.htm) and I'm not sure if you want to make the vfd by software; there's a lot of brands out there that already do it!!! so you don't have to worry about to make the ramps, you just have to worry to start and stop the vfd. You have to program the VFD to make the ramps that you want, so you just need to program a plc output to start and stop the vfd; I already did this using a micrologix 1500 and the vfd from altivar ATV58 D54N4 (http://www.schneider-electric.ca/ww.../html/atv58.htm), my application was to control a motor working at 440 VAC, 60hp so that's why we choose this vfd but it would depend from your application. Hope this give you an idea. Regards

Click to expand...

mortiz, what was your first step to do a vfd to control a induction motor 3phase, ac? i m doing an assignment that requires me to control a 3phase acmotor, can you advice me where to start, as previously.. i only did ladder programming, and hasn't been so real application before.

please suggest, which aspect should i start, at . HSC? or does it requires timers and counters? i r using logicmaster 90 by gefanuc


my application is to control a motor, to brake , stop, start, as well as reverse n forward motion of the IM motor, no feedback. just a crude control over it.
p;lease advice. thank u

If you step back and just look at the AC drive input requirements, or, to look at it another way, the PLC output requirements, then I gather from your posts above that you will need the following:

A PLC relay output that closes for motor RUN and opens for motor STOP

A PLC relay output that closes for REVERSE direction and is open for FORWARD direction.

A PLC analog output, either 0-10VDC or 4-20maDC, that represents the desired motor speed.

It sounds like the encoder you mention is on some other piece of equipment and the idea is to get the VFD/motor system to follow the encoder signal. When you are operating in this way, normally you will set up the VFD accel/decel ramps very short and let the speed signal from the PLC govern the accel/decel ramp times. If you don't do that, then, on very fast speed change instructions, the VFD will use its own slower accel/decel ramps and lag behind the PLC speed instruction. That's usually unacceptable for follower applications.

If you don't have an analog output card in your PLC and don't want to add one, there is a VFD control scheme that has no analog input but rather uses one relay contact output to increase speed and another to decrease speed. This is commonly called "MOP" or "floating point" speed control. It's a little harder to set up in the drive but might be useful in your situation.

You mention braking. This capability usually requires an additional module or at least a braking resistor added to the drive. Standard drives are not normally capable of much braking. Your PLC will not have to do anything special to use the braking feature. Braking will occur automatically when the VFD tells the motor to slow down at a steeper rate than the load will naturally coast down. If you get a fault on the drive that is named "Overvoltage" or "High DC Bus", that is a sure sign that you have exceeded the braking capacity of the drive and will either have to increase the braking capacity or lengthen the decel ramp to reduce the braking energy.

HOpe this helps you get started.

If you step back and just look at the AC drive input requirements, or, to look at it another way, the PLC output requirements, then I gather from your posts above that you will need the following:

A PLC relay output that closes for motor RUN and opens for motor STOP

A PLC relay output that closes for REVERSE direction and is open for FORWARD direction.

A PLC analog output, either 0-10VDC or 4-20maDC, that represents the desired motor speed.

It sounds like the encoder you mention is on some other piece of equipment and the idea is to get the VFD/motor system to follow the encoder signal. When you are operating in this way, normally you will set up the VFD accel/decel ramps very short and let the speed signal from the PLC govern the accel/decel ramp times. If you don't do that, then, on very fast speed change instructions, the VFD will use its own slower accel/decel ramps and lag behind the PLC speed instruction. That's usually unacceptable for follower applications.

If you don't have an analog output card in your PLC and don't want to add one, there is a VFD control scheme that has no analog input but rather uses one relay contact output to increase speed and another to decrease speed. This is commonly called "MOP" or "floating point" speed control. It's a little harder to set up in the drive but might be useful in your situation.

You mention braking. This capability usually requires an additional module or at least a braking resistor added to the drive. Standard drives are not normally capable of much braking. Your PLC will not have to do anything special to use the braking feature. Braking will occur automatically when the VFD tells the motor to slow down at a steeper rate than the load will naturally coast down. If you get a fault on the drive that is named "Overvoltage" or "High DC Bus", that is a sure sign that you have exceeded the braking capacity of the drive and will either have to increase the braking capacity or lengthen the decel ramp to reduce the braking energy.

HOpe this helps you get started.

Click to expand...

thanks . it is useful

dicky, the plc controller i r using now is
http://www.geindustrial.com/cwc/gefanuc/support/ControllersIO/s90micro.htm

if i r going to get a vfd, does vfd's is PLC selective? can i use aany vfd module on this PLC i m currently using? sori if i ask'd ireelevent question but i it is my first time, if it goes well, i going to purchase a vfd, not yet decided, for my project,

thanks plz advice plz

i m using the upper module, yes, the longer 1.

crying_baby:

A VFD is a box. It is a piece of hardware. At the most basic level, it has terminals to connect to line power, terminals to connect to a motor, terminals to connect a RUN contact (from ANY PLC), and terminals to connect a SPEED REFERENCE (an analog signal source).

It is not a 'Module' for any specific PLC.

With what you described in your other post, you don't even NEED a PLC to control it. Just hook up Power, Motor, Start Switch, Reverse Switch, and a Potentiometer. Bingo. Project DONE.

A VFD is a box. It is a piece of hardware. At the most basic level, it has terminals to connect to line power, terminals to connect to a motor, terminals to connect a RUN contact (from ANY PLC), and terminals to connect a SPEED REFERENCE (an analog signal source).

It is not a 'Module' for any specific PLC.

With what you described in your other post, you don't even NEED a PLC to control it. Just hook up Power, Motor, Start Switch, Reverse Switch, and a Potentiometer. Bingo. Project DONE.

Click to expand...

everything makes sense now. thank u rash

but then, vfd can acept ladder programm from a plc still rite

Crying Baby I have provided this information already but will do it once again...read it this time.
http://www.patchn.com/what_is_a_drive.html

http://www.patchn.com/vfd.html

http://www.patchn.com/mtrwhtpaper.htm

This thread refered to AB 160 SSC:
http://www.ab.com/drives/160c/index.html
This is what it looks like

This is the manual: http://literature.rockwellautomation.com/idc/groups/literature/documents/um/160-um005_-en-p.pdf

This some of the terminal options

crying_baby said:

everything makes sense now. thank u rash

but then, vfd can acept ladder programm from a plc still rite

Click to expand...

The PLC is programed to produce output signals which you must connect/wire to the AC drive inputs to tell the drive what to do.

Your not doing the reading as I had requested.
If you had, you wouldnt be asking these questions.