Hi All,
I would like to know if there is a optimal design for PLC Output stage with 0.5A Output current and under 500Hz switching.

 

??Is this a design for a custom PLC design?

 

IEC 61131-2 specifies (classifies) the types of PLC IO. There should be wiki's and various references on line without needing to access IEC 61131-2.

Using that terminology... you should be able to find standard ICs that provide compliant PLC IOs of the desired type. Of the top of my head Maxim (now Analog Devices) and ST make such ICs. I'm sure others do as well.

Even if you want to design your own interface you'll learn some things by studying the datasheets for these ICs.

 

Certainly THERE IS a design for a PLC DC output able to handle 0.50amps at a frequency of up to 500 Hz. But it may not be available for the brand of PLC the TS wants to use.
Given the lack of additional information, I present a limited answer.

 

I am desiging an application specific PLC System and want the system to be Robust in terms of EMI (System Will Work near 3.3 kv generator) Short Circuits and ambient interference.

 

??Is this a design for a custom PLC design?

Yes

 

I am desiging an application specific PLC System and want the system to be Robust in terms of EMI (System Will Work near 3.3 kv generator) Short Circuits and ambient interference.

The term "Application-specific" is at odds with the concept of "PLC" and PLCs are already hardened against EMI. Have you tried an off-the-shelf PLC already and experienced issues or are you just assuming it won't work? Or are you reinventing the wheel on purpose to make the system proprietary?

 

I am desiging an application specific PLC System and want the system to be Robust in terms of EMI (System Will Work near 3.3 kv generator) Short Circuits and ambient interference.

Terminate all earth GND's to a central star point together with a good Earth GND conductor.

 

The term "Application-specific" is at odds with the concept of "PLC" and PLCs are already hardened against EMI. Have you tried an off-the-shelf PLC already and experienced issues or are you just assuming it won't work? Or are you reinventing the wheel on purpose to make the system proprietary?

ALL PLC control programs are application specific, unless one is cobbling a specific program out of a universal control program example. Normally code is written to run the machine motions in the sequence the machine is supposed to run in. So just as many machines are "application specific" so the machine code sequence must fit the application.
In an application area with high voltages and large currents, adequate shielding and proper design are called for. That might include a steel enclosure and filtering on all external wiring, and shielding for all control input wires.

OR, is the TS designing a module for a PLC that is immue to all of that high level interference?? That would be a very big challenge because working with the internal PLC data and control bus will require understanding all of it, and they may not be willing to share that information.

 

ALL PLC control programs are application specific, unless one is cobbling a specific program out of a universal control program example. Normally code is written to run the machine motions in the sequence the machine is supposed to run in. So just as many machines are "application specific" so the machine code sequence must fit the application.

I thought it was obvious I was referring to hardware, not programming. That's what the thread is about. Of course the programs are application specific.

PLCs are microcontrollers with a fortress of industrial hardened support circuitry built around them. They are already EMI resistant, having been built with the intent to be installed in cabinets right beside some extremely noisy devices, like for example 6" away from a 100HP VFD.

This thread is tantamount to "I am designing my own car because I need 4-wheel conveyance that runs on gasoline. Please tell me how."

 

NOTHING WAS "OBVIOUS" from what I read.
I have never come across any wanting to design their own PLC I/O hardware modules, not in all the time that PLCs have been available. So that portion did not make any sense to me.
Packaging a PLC system to prevent outside interference is very common, however. That is quite common and information was often published as to how it was accomplished.

The most certain way to assure that the PLC package is unaffected by anything is to have it in an adequately isolated enclosure and connected to the I/O in the high-noise area by means of fiber optic cables of adequate length. Then the only concern would be for isolation of the operating power for the remote I/O, which is a mature technology.

 

I have never come across any wanting to design their own PLC I/O hardware modules, not in all the time that PLCs have been available. .

I have had to do this on many occasions when implementing a PC based DIY CNC control system, Industrial CNC's have the PLC built in, but Where PC based control is used implementing Galil motion cards etc, I use the Opto-22 range for I/O.

e.g.: (an older board)

 

BTW, @Dragonoid , the Opto-22 site give the internal schematic for all their modules.

 

Neither a "PC" nor a CNC controller, not OPTO-22 I/O boards come close to what I consider a PLC package.
They are all quite good products but not a PLC.

 

Neither a "PC" nor a CNC controller, not OPTO-22 I/O boards come close to what I consider a PLC package.
They are all quite good products but not a PLC.

Maybe you are not that familiar with CNC?
All the commercial ones I have worked on have what essentially is a separate PLC to the CNC motion controller, they communicate with each other over a common buss.
But are virtually identical to any Descrete PLC I have worked on.
i.e Display ladder and are programmed identical in every respect, all with the same type I/O.
I refute the claim they cannot be considered a 'PLC' !
I Implemented Mitsubishi CNC controllers into retro fits for many years and the PLC imbedded in the CNC system was virtually identical to their stand alone PLC versions.
Of which I also have used extensively

 

Also I did not say that the Opto-22 I/O was a PLC ?
The OP requested I/O details. "I would like to know if there is a optimal design for PLC Output stage"
In any case Opto-22 also manuf. PLC's & industrial controllers.

 

@MaxHeadRoom & @MisterBill2 I am conflicted, I actually agree with both of you.

I am familiar with some CNC controls and some have what I consider a "real" PLC but others have some PCBs that are "technically" PLCs but are not what I refer to when I say "PLC."

For example I have a CNC mill that I retrofitted with LinuxCNC and Mesa control boards. These boards handle 5-32V I/O and logic can be programmed in a "ladder" approximation.

This is in contrast to Fanuc, Siemens, Mitsubishi, et al. systems I have worked on, which had a separate PLC, obviously a "real" PLC.

What I mean by "real" PLC is the traditional easily recognizable PLC form factor; Power supply, processor, and I/O all in modular enclosed "card" form with a backplane or stackable architecture, with graphical ladder programming capacity and the ability to upload from the PLC.

 

@MaxHeadRoom & @MisterBill2 I am conflicted, I actually agree with both of you.
I am familiar with some CNC controls and some have what I consider a "real" PLC but others have some PCBs that are "technically" PLCs but are not what I refer to when I say "PLC."
For example I have a CNC mill that I retrofitted with LinuxCNC and Mesa control boards. These boards handle 5-32V I/O and logic can be programmed in a "ladder" approximation.
This is in contrast to Fanuc, Siemens, Mitsubishi, et al. systems I have worked on, which had a separate PLC, obviously a "real" PLC.
What I mean by "real" PLC is the traditional easily recognizable PLC form factor; Power supply, processor, and I/O all in modular enclosed "card" form with a backplane or stackable architecture, with graphical ladder programming capacity and the ability to upload from the PLC.

Well Fanuc, Mitsubishi et-al, use the same Boolean logic display, together with the same type of I/O interface, with all the methods for trouble shooting essentially making it practically and visually identical to a Descrete PLC.
They just implement the PLC using a separate processor within the same controller and communicate with each other over the buss and basically have no direct influence, of one over the other.
These upload/download the PLC content just as any Descrete type does.
I agree there is some low end DIY systems that simulate the functions, but do not fully implement the typical 'PLC' as it is defined.
My main definition, is whether or not it has the capability to display the Boolean logic display and together with the status of the Boolean functions.
It was the comment made that the " CNC PLC does not come close to a PLC package" which I definitely refute.

 

The fact that a CNC package has a section that can be programmed with ladder logic, and may even have similar I/O, does not make it a PLC. It is still a CNC device that can run ladder logic while it is doing CNC magic stuff, like driving multiple axis to produce curves.
Of course, with those systems that add motion control to standard PLC functions, they do blur the line between the types. But the CNC packages I have seen all included a panel for entering the control values, which I have not seen on any PLC that I have used so far. BUT I do mostly use the less expensive PLC models.

 

Interesting. A PLC (Programmable Logic Controller) works with timers and relays. All you need is a set of timer circuits using say sets of RC Timers with each timer going to a comparator with some hysteresis along with a simple threshold detection limit (preferably with some Hysteresis. These drive the relays. Then you just use ladder logic. Is that what the TS is asking for?