PLC Sizing

Hi all,

i am planning to work on a project where 50-60 AC/DC motors are to be started on pre-determined time & sequence.

this is to be done with the help of a PLC ( + HMI optional)

Now can somebody provide me some help on the correct sizing of the PLC or suggest me the best PLC or Expansion modules which will accomplish the task.

secondly the PLC must be available ( or made available ) in INDIA.

earlier i have programmed the PLC for NC / CNC hydraulic machines....so programming is not a problem...!

any suggestion or help is appreciated.

thanks.

Hi, you will need one output per motor, total then 50 - 50 outputs.
If the program is not too sophisticated an Allen Bradley micrologix with two 32bit ouput expansion cards will do. Put into consideration an amount of inputs (overloads, emergency stop healthy, starts, stops, auto, manual, ...) so you may need two input expansion cards as well.
Thos PLCs are widely available and fairly cheap and easy to program. The software for an 1100 processor is free and it can take up to four expansion cards. Hope this helps.

Stigma1967,

I would do the following for each motor

Inputs
1. motor start pb
2. motor stop pb.
3. motor contactor energized.

Outputs.
1. motor contactor.

there are a lot of variables yet to be determined.
spares - you always forget something.

james

An HMI would save you a lot of IO for selections such as Auto/Manual control. Is there any interlocking...like cant start motor 1 if motor 2 is running

hi guys...actually the whole system is at present running in conventional way....like each motor has individual controls....ON / OFF , OL protection etc. but it is manual.....each motor needs manual start and stop.....
I am supposed to convert the same in to PLC logic...of starting the motors in sequence...instantly or with certain time delay...after each motor starts. basically it is mill with lots of conveyors...involved.
any one of these ( 50-60 ) motor fails or fails to start for any reason...then Shut Down sequence is to be initiated ....with pre-determined sequence.
that's the idea.....as far as things stand i would need.....A Good Rugged PLC with 60-80 Outputs.....and around same inputs.....and about 60-80 Hardware relays ( SPDT or DPDT ) to activate the contactor coils, hooters and Indicator lights....

kindly suggest.....thanks.

Stigma1967 said:

hi guys...actually the whole system is at present running in conventional way....like each motor has individual controls....ON / OFF , OL protection etc. but it is manual.....each motor needs manual start and stop.....
I am supposed to convert the same in to PLC logic...of starting the motors in sequence...instantly or with certain time delay...after each motor starts. basically it is mill with lots of conveyors...involved.
any one of these ( 50-60 ) motor fails or fails to start for any reason...then Shut Down sequence is to be initiated ....with pre-determined sequence.
that's the idea.....as far as things stand i would need.....A Good Rugged PLC with 60-80 Outputs.....and around same inputs.....and about 60-80 Hardware relays ( SPDT or DPDT ) to activate the contactor coils, hooters and Indicator lights....

kindly suggest.....thanks.

Click to expand...

Many PLCs on the market can be expanded to 60-80 outputs/inputs. Note that the PLC won't have that many IO built in, you'll need to buy expansion modules for most of the IO.

How far apart are the motors? 50-60 motors sounds like a fairly large system. Odds are that some of the wiring distances could be fairly long, so remote or distributed IO could be useful. Instead of running all the individual wires back, you would use an Ethernet or serial cable.

From Siemens, the S7-1200 family is your best bet for the PLC. It could have all the IO local, but if you want distributed IO, I'd suggest the ET200sp family, or possibly just using multiple 1200's.

In AB, you could probably use a Micrologix. There are a few different families, not sure which would be best. Another poster suggested the 1100

Automation Direct also has multiple PLC famlies that should be expandable into this range.

When you say a "rugged" PLC, most products from most major vendors are "rugged" enough for most applications. Do you have any special requirements, like IP65 (protected from water spray), chemical resistance, or very high temperature (50C instead of 30 or so)?

Most PLC's will do this. Most PLC's are pretty rugged. If I were you I would be doing the following:

Asking the company what PLC's they prefer
Looking at local Controls Distributors and talking to them to find availability
Looking at price

The availability of parts and support are paramount to initial cost in my mind. From that point on you are then deciding exactly WHAT PLC you want to use. Using relays just about any IO system will work as long as it is modular. One thing to keep in mind is going to be the maximum number of IO points allowed in the system. It sounds like you will need quite a few.

Even if you use an HMI you are going to want some kind of hardwired controls so that if the HMI goes down you can still start the system and most definitely will want hard-wired stops for safety. The system won't hurt anyone if it won't start, but it most certainly will if you can't stop it.