I was just speaking in general. I don't have a specific application to spec, just thinking of getting into the field. Is data input directly or through software downloaded through a computer? How do you generally change data?
The "Learn PLCs" link at the top of the page is a good place to start when you have a general question such as this.
I would also recommend registering for the forum. It's fast, free and (relatively) painless Also, you will find that if (or when) you have more specific questions, the experts at this site will be more than willing to help you out...
I was just speaking in general. I don't have a specific application to spec, just thinking of getting into the field. Is data input directly or through software downloaded through a computer? How do you generally change data?
Both ways, and many more... The other thing, there are many types of data, and apart many data types could have many different interfaces to the field devices... For example an analog signal could use a 4-20ma signal or 0-10vdc or many others... WOW, such a simple question but a very complex answer... Most PLCs use special input and output cards designed for the specified devices. Intern each device would be wired to a channel on the card (typical) however you can change data through communications to other PLCs, PCs, and many more things that I have never used....
It depends on the I/O you have and in essence what you are doing in your application.
It also depends if you are using an operator interface or not.
The structure of the program basically remains the same. What you are changing is variable information - timer and counter values.
With some controllers, this can be done on the fly through the programming software. With others, you would have to make changes, recompile and download your new program.
If you are using an operator interface, and it is set up by the OEM for you to access register information, then you would be able to change it that way.
A third way would be through an HMI software interface.
There are other devices that can interface to the PLC that will allow you to access the controller and change data, such as a modem.