New to PLC's and have a very basic question

[Etang858]

Hello Everyone,

I am brand new to PLC's (learned they even existed 3 days ago) and have gone through the tutorial on this site. I am a little confused and was hoping for some clarification.

My question regards the basic communication between PLC, computer and actuators.

1. Lets say I purchase a PLC and need it to move an actuator. The PLC will connect to the actuator via its inputs and outputs and the computer will connect to the PLC via 'something'. The PLC then has software where I can do ladder programming on my laptop, (This is how I assume this system would all connect).

Is this software able to communicate with the PLCs or is it purely for ladder logic?
Is there another type of software/communication protocol I need to actually have the PC communicate with the actuator?

I've seen some stuff about MODBUS, OPC servers and OPC-aware software and that's where I get confused.

I know these are basic questions but any help would be appreciated.

If you guys know of any other good sites where I can learn about PLC's and choosing PLC's for applications, it would be much appreciated!

Thank you!

 

[sthompson]

1. Lets say I purchase a PLC and need it to move an actuator. The PLC will connect to the actuator via its inputs and outputs and the computer will connect to the PLC via 'something'. The PLC then has software where I can do ladder programming on my laptop, (This is how I assume this system would all connect).

The Computer will connect to the PLC via some kind of Communications. This is a varied as the PLC Manufacturer and Model.

It might be Ethernet, Serial RS-232 or RS-422, AB DH+ or DH485, Modbus Serial or TCP, and on it goes. This will depend on the Manufacturer, Model, and Options, and is part of the buying decision.

The Programming Software runs in your Computer, not in the PLC. The PLC Program that you write with the PLC Programming Software runs in the PLC.

Is this software able to communicate with the PLCs or is it purely for ladder logic?
Is there another type of software/communication protocol I need to actually have the PC communicate with the actuator?

The Programming Software may communicate directly with the PLC or go through another Program such as AB RSLinx. Again it depends on which PLC. There are also HMI Programs that can communicate with the PLC for SCADA and Operator Control.

Is there another type of software/communication protocol I need to actually have the PC communicate with the actuator?

The PC does not communicate with the Actuator, the PLC does. There are some exceptions known as Pass Through were smart devices can be accessed through the PLC.

www.mrplc.com and www.control.com have a lot of tutorials.

Hope that helps.

Stu.....

 

[Etang858]

Thanks for the reply Stu
So let me make sure I understood this...

Computer connects to PLC via serial port or some other physical connection. The computer I will be using will only have USB and Ethernet connections so I'm assuming I will need a Ethernet connection module.

I create ladder logic on the computer using software,
This ladder logic is communicated to the PLC via MODBUS (MODBUS is just chosen for sake of example),
Then the PLC communicates to the actuator and moves via direct software communication or something like AB RSLinx?

Still a little confused...great help so far though

Thank you!

 

[Gil47]

Take a look at Ron Beauforts material
The UTube videos are very good

http://www.ronbeaufort.com/

 

[sthompson]

Computer connects to PLC via serial port or some other physical connection. The computer I will be using will only have USB and Ethernet connections so I'm assuming I will need a Ethernet connection module.

Correct, many of the newer PLCs directly support Ethernet, and they are even moving to directly support USB. Laptops with Serial Ports are getting rare these days. Many PLCs still use Serial though, or Serial to some other communications method. Use caution with USB to Serial converters, as many do not work well with PLCs. Many have had good success with the Keyspan HS-19 available here http://www.plctrainer.net/PLCCommunication.htm and other locations.

I create ladder logic on the computer using software,
This ladder logic is communicated to the PLC via MODBUS (MODBUS is just chosen for sake of example),

Correct, the Programming Software converts it to a form understood by the PLC, and you Download it to the PLC via the Communications Method. Many PLCs also support Online Programming, which allows you to make changes to the running PLC Program. There are some limits in most, for instance in most Allen Bradley PLCs, you can't create or expand Data Files.

Then the PLC communicates to the actuator and moves via direct software communication or something like AB RSLinx?

Incorrect, RSLinx resided on the Computer, and is used as Communications Server for Programming or HMI Software on the Computer. For example, RSLogix 5, 500, 5000, and RSView which is a Graphical Control Program. Basically an HMI (Human Machine Interface) running on the Computer.

The PLC controls the Actuator using Outputs and Inputs if they are an On/Off type of device i.e. Motor Starters, Solenoid Valves, or Analog Outputs i.e. Proportional Valves, VFDs, and Analog Inputs i.e. Flow Meter, Pressure, Temperature.

Why don't you start with the Online Tutorial on this site.

http://www.plcs.net/contents.shtml

There is also a PLC Simulator if you are registered.

Stu....