Start Stop VFD via Speed Reference 2

[powersoff]

I would like to start and stop a PowerFlex 40 with a 4/20ma signal.
Can this be done?
Is it a bad (stupid/won't work/troubleshooting nightmare )idea to use the PowerFlex40 24vdc internal power to source transducer?

Thanks

 

[Skogsgurra]

Yes, it can be done. But your drive will not be stopped, just running with around 0 RPM, which can be all you need or it can be totally unacceptable. Mostly, it is not acceptable.

I would check very carefully before using the internal 24 V supply. It can not deliver more than 100 mA and part of that current will be used for the digital I/O. Also, most 4-20 loops are supposed to be floating - taking the supply from the drive itself means that it isn't floating anymore.

Could work, but you need to do some checking on your own.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[powersoff]

I would like the drive to stop when reference is <12mA(30hz) and restart when the reference is >16mA(45hz).

 

[jraef]

Some drives allow that, some do not. Some also have a feature often referred to as "Sleep Mode" because essentially the drive will go in a partial shutdown when the speed reference drops below a specified threshold.

As to whether or not the PowerFlex40 has those capabilities, A-B should be able to tell you. But be prepared to give them a credit card for an answer.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[ScottyUK]

The Powerflex 70 definitely has that feature, but it doesn't seem to be available on the Powerflex 40 according to the parameter lists on AB's website.

You could use an external 'trip amplifier' to give you a relay contact which opens at 12mA and recloses at 16mA and use that to control the drive start input.


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If we learn from our mistakes I'm getting a great education!

 

[waross]

A 4-20 ma alarm relay with adjustable dead band may work.

Bill
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"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Hi Bill,

Over here that's what we know as a 'trip amp'. Guess it's a British name.


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If we learn from our mistakes I'm getting a great education!

 

[waross]

I'm feeling a little redundant just now. grin.
On the other hand it looks like two votes for the same device by whatever name.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Divided by a common language.


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If we learn from our mistakes I'm getting a great education!

 

[DickDV]

Some drives have level detection capabilities on their output relays. If yours does, set the relay to input reference and set the level to 12ma. Then connect the relay contacts to the run input on the drive.

I am sure the ABB drives have that feature. Not sure about AB.

 

[powersoff]

For future reference A055"Above Freq 6" and A056 (Relay Out Level).

Thanks DickDV.

 

[Compositepro]

Most analog servo drives I've used have a "zero speed relay" which will basically activates the "stop' function when the speed reference drops below a certain voltage.

 

[toygasm4u]

Wow.. this is one of those rare occasions when I actually have an answer to a question on this forum!

On the PF 4, 40 and 4M, you have a 4-20mA and 0-10VDC input. Since your analog signal is 4-20mA, you would naturally want to use the 4-20mA input on the drive, but that's not necessary. Drop your 4-20mA signal across a 500 ohm resistor to develop 2.0-10.0 VDC. Then use your drive's 0-10VDC analog input for speed reference. (This will be thrown off just a tad; the drive's input impedance is around 11k). By now you're asking "why?".

Dig into the PF drive's Advanced parameter group and look at A055 [Relay Out Select]. Option 10 - "Above Anlg V". Using this option, you can set up a threshold switch using your analog as a trigger. Your threshold is then adjustable via A056 [Relay Out Level].

Once you've got the threshold switch setup, you can drop the Relay's NO contacts across Digital input 1 for 2-wire start stop. With a little trimming on the Analog offsets, scaling values, etc, you can nail it down to perform very accurately.

*Poof*. Now you've got a legit start/stop and speed reference using just a 4-20mA. I've done this several times on various projects; works like a charm.

 

[powersoff]

Thanks for the replies.

I still am not sure why people intentionally use AB stuff.
Yaskawa P7, IQpump Controllers(a awesome drive for pump applications) and even the lowly Altivar 21 have this functionality built in without all the hurdles.