Test

[randy]

I’m taking an evening class at our local community college. The course is Industrial Electronic Control Systems. My instructor kind of veered away from our topic that evening, which was Process Control Methods, and got on to PLC’s. He worked out a PLC logic program on the blackboard, which he was using one momentary push button to activate a discrete output and using the same button would de-activate the same output. He was trying to manipulate the scan sequence, which is from top to bottom, left to right. He worked out the problem on the board and at that time it did seem to make sense, but I was not 100% sure.

I have a Mitsubishi FX2N PLC at home to practice on in my free time. So I went home to try his logic on my system. This did not work and before I confront my instructor, which I have not received my grade yet, I want to be sure. Please review the logic and please tell me what I am missing…



--[PB1]--[M1/]----------------------------------(M0)

--[PB1]-----------------------------------------(M1)

--[M0 ]--[M1]-----------------------------------(M3)

--[M0]--|--[M3/]--------------------------------(Y0)
--[Y0]--|

Thanks

[rsdoran]

What it boils down too is that M0 cant energize Y0 because M1 is on after MO which basically turns off M0 before rung that energizes Y0

[Steve Bailey]

In the third rung, the M1 contact should be a Y0.

[PLucas]

I think you will find that this would work for using the same switch
to turn an output on then off

--[PB1]--[M2/]----------------------------------(M1)

--[PB1/]-----------------------------------------(M2)

--[M1 ]--[M3/]-|---------------------------------(M3)
|
--[M3 ]--[M1/]-|

--[M3]-------------------------------------------(Y0)

[rsdoran]

What holds Y0 latched? Am I missing something?

[Eric Nelson]

There are a bunch of ways to do this. How about this one?...

(enlarged for your viewing pleasure)

   PB1     M3      M2

---| |-----|/|-----| |-----(M1)



   PB1     M3      M1

---| |-----|/|-----|/|-----(M2)

                |

    M2          |

---| |----------'



   PB1

---| |---------------------(M3)



   M2

---| |---------------------(Y0)

Output Y0 will change state each time PB1 is pressed

(Copied from a working program, so it's valid)

-Ericbig

[rhoog]

I do this by using a counter. The momentary input increases the counter by 1. Then just use the bit in the counter that is true when (counter val=1) for the output status. The counter resets its self to 0 after the second press of the button (counter val = 2). You do not need to use any latches as the output will consantly relect the value in the counter. This only requires 3 lines of ladder logic.

[Chris Davidson]

Hi
A point of interest for Mitsi FX programmers is the ALT instruction. This is a predefined way of using a momentary pushbutton to toggle coil states. Saves all the other grief.

Chris