Hard wiring the PLC

HEY!!

Anyone notice? We haven't heard from Doug H. since his OP. Just stirred up the hornet's nest and is sitting back watching.

Hope he's having as much fun as I am.

: )

Stationmaster
 
PeterW said:
Small ones are inexpensive.

When you have 22 motors driving the same thing, then its cost effective to have a single inverter (or grouped motors, 8 per inverter for example).

Also sometimes if you have two things that run at the same time and you want same speed that variable, then again you may have just one.

OK. I have politics put VFD/Motor with fieldbus control. Nothing else not needed, no digital i/o etc. VDF protect itself and the motor, so smallones (VFD) can be after common circuit braker.

After common VFD I can't be sure have the motors same split and equal loading. VFD itself can control split or I can do it by PLC software.
 
seppoalanen said:
OK. I have politics put VFD/Motor with fieldbus control. Nothing else not needed, no digital i/o etc. VDF protect itself and the motor, so smallones (VFD) can be after common circuit braker.

After common VFD I can't be sure have the motors same split and equal loading. VFD itself can control split or I can do it by PLC software.

control word using Fieldbus or Digital I/O, both OK, I'm used to using Profibus myself.

VFD will protect the motor and to an extent itself, but would still need infeed protection.

A Safety contactor wold be needed, as you cannot guarantee the VFD will not develope a fault.

For multiple drives the VFD will supply the same to all drives, the PLC cannot do anything.
 
A Safety contactor wold be needed, as you cannot guarantee the VFD will not develope a fault.
This statement has been made a few times, you use fuses or CB in front of a drive, this does not seem to me to apply as a safety factor to me. If you have power quality issues those should be addressed but I guess there may be situations where you have multiple VFD's in a panel where certain ones should be OFF while others left on.

For multiple drives the VFD will supply the same to all drives, the PLC cannot do anything.

Multiple motors the VFD will supply the same too all.
 
Last edited:
Stationmaster said:
uh............What??

Stationmaster

Sorry I was answering

'After common VFD I can't be sure have the motors same split and equal loading. VFD itself can control split or I can do it by PLC software.'

Pointing out the PLC cannot influence the loading between drives after the PLC.

rsdoran said:
This statement has been made a few times, you use fuses or CB in front of a drive, this does not seem to me to apply as a safety factor to me. If you have power quality issues those should be addressed but I guess there may be situations where you have multiple VFD's in a panel where certain ones should be OFF while others left on.
Stationmaster

By safety I mean, someone pressing an E-Stop or openning a guard.
 
PeterW said:
Sorry I was answering

'After common VFD I can't be sure have the motors same split and equal loading. VFD itself can control split or I can do it by PLC software.'

Pointing out the PLC cannot influence the loading between drives after the PLC.

I think my UK translator may be malfunctioning.

: )

If I may wax "pedantic" for a moment,

Are you trying to say "the PLC cannot influence the loading between 'motors' after the 'VFD'? (which I understand and agree)

Or am I missing out on some concept that may add to my "bag of tricks"?

Stationmaster
 
Last edited:
Thats not a UK flag for seppo, its Finland.

I do not necessarily see a safety advantage by removing power from a Drive, same as a PLC, but it all depends on the application.
 
rsdoran said:
Thats not a UK flag for seppo, its Finland.

Yeah, I was actually referring to PeterW, HIM I'm supposed to be able to follow. And yes I know his flag is Canada, but I thought I remembered him saying he came from UK. I could be wrong. So many members, can't really keep track.

I think he got my drift :)

Stationmaster
 
rsdoran said:
Thats not a UK flag for seppo, its Finland.

I think he maybe referring to me as I'm not long in my 'adopted' country. 🍺

rsdoran said:
I do not necessarily see a safety advantage by removing power from a Drive, same as a PLC, but it all depends on the application.

I cannot see the advantage on the PLC either, as a matter of fact you risk creating a problem in the PLC by powering it down all the time. You don't power down the PLC, just motive force, which means dropping the power to the motors.

For an inverter, now this is different, the output of the inverter is the motive force.

Therefore unlike the PLC, where a programming, setting or hardware fault will not cause injury or death on an E-Stop being pressed or a guard opened as the power is dropped externally, an inverter with a problem can continue to drive the motor.

Therefore, the power has to be removed to enure safe operation for someone to access the equipment.
 
Stationmaster said:
Are you trying to say "the PLC cannot influence the loading between 'motors' after the 'VFD'? (which I understand and agree)
Stationmaster

Sorry my finglish..

Maybe I miss-understand your point, but anyhow we can get power, torque, current, frquence, DC-volt etc. via fieldbus from VFD to PLC.
Secondly we know nominal split of motor in nominal power. So we have many calculating tools for motor split correction with current power and current frequence.
We have 2 way control the Speed, Frequence ref or Speed ref.
With frequence ref split must correct by PLC-program.
With speed ref 'good' VFD do it itself ('cheapones' can not).
This is important f.e. for paper roll conveyors. Outermost paper 'teares' when paper roll moves from conveyor to conveyor and conveyors have different speeds.
Main point is that 'squirrel gage motor' runs with same parameters allways in the same speed, this is physical fact!

Interlocking signaals between PLCs.
There are "2 kind of air", via f.e. Ethernet or via digital-I/O. Both are hard-wired in my mind. In Ethernet world we can make multicast groups and control that messages comes from senders enough often.

Seppo
 
seppoalanen said:
Sorry my finglish..
It is unfortunate, but I do not understand the fine points of most of what you are trying to say.

seppoalanen said:
Maybe I miss-understand your point,
The "point" that you quoted was to intended to try to clarify a point made by PeterW.

seppoalanen said:
Main point is that 'squirrel gage motor' runs with same parameters allways in the same speed, this is physical fact!

The one "main" point I think I understand - I disagree, (a little). Don't forget "slip". Different motors can have different slip. Identical motors with different loads can have different slip, maybe different enough to tear paper.

Best Regards,

Stationmaster
 
Regarding the removal of power for safety purposes:


PeterW said:
I cannot see the advantage on the PLC either, as a matter of fact you risk creating a problem in the PLC by powering it down all the time. You don't power down the PLC, just motive force, which means dropping the power to the motors.

For an inverter, now this is different, the output of the inverter is the motive force.

Therefore unlike the PLC, where a programming, setting or hardware fault will not cause injury or death on an E-Stop being pressed or a guard opened as the power is dropped externally, an inverter with a problem can continue to drive the motor.

Therefore, the power has to be removed to ensure safe operation for someone to access the equipment.

Well put, I couldn't agree more.

Stationmaster
 

Similar Topics

Is it ever permissible to run I/O wiring in the same conduit as 480 volt 3 ph motor wiring? I have a dispute going right now.
Replies
40
Views
9,684
I was working with a licensed electrician in another state. He had a 220 contactor wired with the supply coming up through the bottom, and his...
Replies
13
Views
4,190
Hi - I'm a newbie to the PLC world but was recently asked if we could store more than the 2G that the CompactLogix 5370 allows by its max size SD...
Replies
13
Views
1,249
It's Saturday, so I thought it would be amusing to look at times gone by, imagine if you had to carry this to site "IBM 5mb Hard Disk 1950's.
Replies
16
Views
1,800
Any help appreciated, Proposed question: I need to track parts to count the rejects in a rotating machine but having no luck tracking proper...
Replies
7
Views
2,317
Back
Top Bottom