I have been asked to build a PLC demo system. The following modules are available to me:

SLC 5/03
8-channel DC Input Module (24VDC)
8-channel DC Output Module (24VDC)
4-Channel Analog Input Module (-20...20 mA or -10...10 Vdc)
4-Channel Analog Current Output Module (0...20 mA)
Chassis and PSU

So basically, I have all my computer hardware. Now I must select some "field devices."

I can think of a few things to do with the digital points (buttons, switches, lights). My problem is how to utilize the analog points.

I really want to implement a PID control loop that utilizes AI and AO.
But the only examples I know of use industrial control valves or pumps with VFDs.

These things are not only huge, but prohibitively expensive. Do any of you know where I might look around to find some devices that would be more of a miniature scale?

Thanks for any resources you can suggest for finding gadgets.

 

Moin Walter,
moin all,

you have several analog I/O channels. Use one pair for Your PID control
- i.e. input for current value and output for control action. Use a
second pair to simulate a plant. Plant input is Your control action
output and plant output will become Your current value input. For the
plant itself any simple or complex simulation could be used. Try with a
PT1 or PT2 first.

Hope this helps
Friedrich

 

The classic demo is a ping pong ball suspended on a column of air in a transparent tube. You need a ping pong ball, a long transparent plastic tube (about 1 metres is typical), a variable speed DC fan or blower, and some sort of non-contact linear sensor that will work in the tube. The challenge is to balance the ball at specified heights. You can introduce process disturbances by restricting the outlet air flow at the top of the tube (e.g. put your hand over it).

Because of the non-linear characteristics of typical fans, and the process lags, this is often more challenging that it sounds.

A water tank demo is another possibility, but it is very hard to get small DC powered water pumps. Parallax used to sell one, but they dropped that product. Aquarium pumps won't work, as they all seem to be AC fixed speed motors.

 

"I have been asked to build a PLC demo system. The following modules
are available to me:"

In course of process-oriented programming, we use virtual objects, so we need no any hardware to teach students, and have a lot of virtual control scenarios to reflect the base situations in control algorithm programming (event-driven behavior, discrete I/O, regulators, time entities, control flow parallelism).

--
Best regards,
Vladimir E. Zyubin

 

M. Griffin,

Thank you very much for the ball/tube idea. I had thought of using a variable speed PC cooling fan, but I could only think of cooling applications.

The ping pong ball is perfect. It will be a good visual for everyone involved. It's also cheap, safe, and portable.

It's also easy to think of ways to use digital sensors along the tube, for example, high level fan shutoff alarm.

Thanks again.

 

A very simple demo setup is to strap a thermocouple to a soldering iron. It gives some time delay and is a little tricky to tune.
In your case you could use a digital output to operate a relay to power the iron (pulse duration) and a t/c to 4-20 transmitter as the feedback.

You could wind your own heater coil from some nichrome wire and operate it directly from 24 volt output.

If you have a budget a couple of tanks with variable speed pumps or control valves and level transmitters would be nice.

Regards
Roy

 

For a small DC powered pump, try a windscreen washer pump from a car scrap yard.