Can a plc control a closed loop process?

All PLC's will do basic math functions, at least all of the ones you
mentioned that I know about. If you need higher math functions then your
going to need a higher priced unit.

LabView is a PC based product, MAC, Windows, Linux at least the way I
understand it.
I tend not to use PC's for control systems. Overhead is to high and they
tend to have a lot of overhead that is not needed for a machine to produce a
product in a lot of cases.

SQLit wrote:


As has already been stated all PLC's will do some math functions. None of
them are geared to anything too complex in the math department.

It strikes me that, if this controller is to be assigned to the machine,
you will have at least two output actuators to control with about seven
process sensor inputs (there may be other peripheral inputs and safety
functions). The required actuators would seem to be the means for moving
the middle roller up and down and the means to move the material to be bent
with one or two degrees of motion (linear through and/or roll round). I
know of a company that use such a machine already and it is a joy to watch
the machine in operation bending pipework in quite fancy designs.

You need to sit down (with pencil and paper) to work out exactly what the
system consists of in terms of all the inputs and outputs. Treat each
actuator separately but note when the sensory feed for both is shared. At
this early stage do not worry about what is going to provide the control.
Just get the control plan very clearly described.

Once you have the control plan (which should include the relational
formulae between inputs and outputs) you should then evaluate the
operational speed and work out the required perfomance of the controller
hardware. Modify the control plan to include this information. Only then
will you be able to ask for further assistance with a well phrased and
specific question about what hardware will properly suit the application.
Do not forget to assess the safety factors for the machine and how you are
going to protect the operators.

The above, I am sure you will be aware, is a more holistic approach to
system development and should yield a control system architecture that fits
the application really well (you may decide that two controllers are
required instead of cramming all functionality into one). As you already
know of some PLC products I expect you may look at those first. However,
you may sometimes find that developing an embedded control system from a
bought in SBC, and adding I/O conditioning to that, would be a less
expensive option (there are lots of free tools available for a variety of
languages and processor families). This would provide the means to do more
complex mathematical functions in less time. The dis-advantage of the
embedded approach is that you may loose the ability to update the programme
with the system running (which most PLC's do quite well) unless you paid a
lot of attention to retaining the ability to do that.

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Thank you so much for your help guys. I'll keep you updated on my
progress.
Thanks loads,
Shay


Paul E. Bennett wrote: