Connected components advice

[cartersrroom]

Connected Components Help

Hi there everyone,

I’m recently new to the PLC world and was hoping somebody might steer me in the right direction.

I’m currently writing a project on connected components V21 and need to do the following task:

A master system is sending me hard wired outputs telling me when certain motors must raise and lower. I then raise and lower these motors and tell the master system via hard wired outputs when the motors have reached their proximity limits.

I’ve written a step sequence for this but don’t think I’m on the right track and would love if someone could just point me as to what wording to use when researching a solution for this on google so I can continue my studies into it.

TIA appreciate it

 

[Jeev]

A lot of the PLC help you find on Google will send you back here Are you able to post what you have and the questions you want answers to? If not, just which Micro800 you are using and what you have so far would be good.

 

[drbitboy]

I’ve written a step sequence for this but don’t think I’m on the right track and would love if someone could just point me as to what wording to use when researching a solution for this on google so I can continue my studies into it.

If
1) the desired output state at any "moment" can be determined from the state both of the inputs and of the outputs from the previous "moment,"
2) all the external inputs and external outputs are booleans (1 or 0; True or False),
3) All of the persistent internal state can be expressed as either booleans or integers (your steps),
4) all the logic can be expressed as boolean operations i.e. AND, OR, NOT, or as comparisons (step nubmer equals some integer constant N)

Then ladder logic in a PLC would be a straightforward, but by not means the only, way to implement such a control system.

PLC programming is primarily about time and the scan cycle is the clock. The key to understanding ladder logic is that each "moment" (above) is a discrete "scan cycle," during which all of the instructions comprising the program are evaluated, top to bottom and left to right. Scan cycles are executed by the PLC operating system (OS) repeatedly and continuously. In between scan cycles the PLC OS queries the physical inputs and copies their states copied into PLC memory; the instructions comprising the program then read those memory locations to determine the current state of the external process when evaluating the program logic.

For example, consider a simple hydraulic system that needs to extend to an outer limit switch, then retract to an inner limit switch. There is also a start/stop button. This would take all of three rungs:

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Adding an integer stroke count to limit the number of strokes, somewhat analogous to your steps, requires but a few more rungs:

​

 

[drbitboy]

Argh, those should be composing not comprising.