Hi, new to PLC's. Need help if you could on a project.

[Sethiroth]

Hello, I am a PC tech/ Database programmer. I have almost no experience with PLC's. I have a question.

I am working on a project where I would like to have say 24 different contact buttons. I want each button to have a "value". Everytime a button makes a connection, I want it to add its "value" to a "total" field. The "total" field will start out at Zero. So if contact button #8 makes a connection, it adds its value (we'll say its value is 200) to the "total" field (0).

So it should do this.

Total = Total + Value.

And then I want another button to reset the "Total" value.

And I want a display of some sort to display the value for "Total" at all times.


How hard would this be to do, and what would I need? Would a PLC board be the way to go? Or would some other way work better?

And what is available for a display? The "Value" field shouldn't ever go higher then six characters.

 

[xJAyx]

This is a pretty simple task for a PLC. You should be able to buy a small PLC with the correct number of digital inputs you need (for your buttons) and an analog output (for your display) and an analog meter with the range of digits you want.
An easier solution wiring wise would be to buy a cheap touchscreen display and have all of your buttons and your display on there. If you do go that route you might even be able to buy a touchscreen that can do the calculation itself.
What else are you doing with the system, ie what do the buttons actually do in the field? That will make a big difference on the hardware you need to use.

 

[Sethiroth]

Well, the touch screen idea is a great idea, but the contacts need to be physical contact switch's, so it won't work in my situation.

Im looking to do about 24 input and maybe 12 output.

I would want four different outputs, each with there own display. The displays needs to be seperate from the PLC. One of the contact buttons will switch focus from one display to the next. So.

Display1 focus = yes
Display2 focus = No
Display3 focus = No
Display4 focus = No

When contact button "SwitchFocus" is made,

Display1 focus = No
Display2 focus = yes
Display3 focus = No
Display4 focus = No

When contact button "SwitchFocus" is made again,

Display1 focus = No
Display2 focus = No
Display3 focus = Yes
Display4 focus = No

Ect...

 

[swhitlock]

Hello!

Sounds like you're doing something interesting, but there aren't many details. The task you're trying to do is quite simple for a PLC, but the solution can vary widely depending on the environment you want to put this in. Without info to narrow it down, here's a whole range of ideas for you:

If you want to do this with standard industrial components that are ultra rugged/reliable, you probably need a PLC and one or more HMIs (displays). The simplest combo would be something like an Allen-Bradley SLC 500 and PanelView "Standard" but I warn you that you also need the programming software. That's not going to be cheap. A less expensive alternative is to go to

http://www.automationdirect.com/

and look at their DirectLogic PLCs and C-More HMIs. These are still good enough quality to use in a manufacturing setting.

However, if your requirements are for a laboratory, prototype or similar not-so-industrial use, there is a less expensive entry level "PLC" you might be interested in:

http://www.tri-plc.com/

If the cost for that is still prohibitive, you could do what you're describing with a custom electrical circuit with a microcontroller running your program. It's fine for hobby projects or if you're creating a prototype for a mass produced commercial product, but you wouldn't use it in a factory. A decent place to start is this website:

http://www.picprojects.247n.com/

The costs would be something like:

Industrial PLC and HMIs: thousands of dollars
Tri-PLC: hundreds of dollars
Microcontroller: tens of dollars

Of course, the time investment on your part would be opposite to that.

I hope that helps. Don't be afraid to ask more questions!

Scott Whitlock
PLC Programming Articles:

http://contactandcoil.com/