PLC Rookie Intern Help?

I am an Intern with on 2 classes in PLCs. I need help on using one input to control six outputs. I need to press the pb one time for the first light. Then press same pb again and next light come. The same pb input to cycle through all six outputs. I have idea how to do this. My first thought was to use a sequecner but cant get the data right. I dont know how to use the same input button to turn on all 6 lights. I want to learn to do it with a SQC and another way. I am a Novice. Please help. Can someone please post a rung example?

Here is one way using relay logic. I am certain that my program could be simplified and/or condensed. There are other ways, including, but not limited to using counters and compare instructions.

RoyChozeh said:

I am an Intern with on 2 classes in PLCs. I need help on using one input to control six outputs. I need to press the pb one time for the first light. Then press same pb again and next light come. The same pb input to cycle through all six outputs. I have idea how to do this. My first thought was to use a sequecner but cant get the data right. I dont know how to use the same input button to turn on all 6 lights. I want to learn to do it with a SQC and another way. I am a Novice. Please help. Can someone please post a rung example?

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You need to use SQO instruction.In the attached image you can see how SQO can be used to do what you have described you want to do in just one rung.

The steps are:
1.Make the same rung
2.Verify it
(I have used 7 lights and have assumed that your sequence is such that at each pushbutton press the next light turns on and the previous one turns off.In case of 6 lights the "Length" in SQO will be 6 and if your sequence is different just modify the N7 data file accordingly.You can change the "Radix" to Binary in the Data File window to make it easy for you to enter the appropriate sequence without having to calculate the decimal equivalent)

Note: You will see that only doing the above will keep cycling through the outputs in a continuous loop.In order to get out of the loop you have to reset the Sequencer by programming the address of your Control Register in the Reset instruction. Place the condition in which you want to sequencer to reset in front of the Reset instruction.

With relay logic, you could use one-shots and latches to sequence the operation of the lights.

My boss wont let me do it with sequencer. I am suppose to use latch and unlatch and a one shot. I am very new to this, very new. I am suppose to use 1 Input with 6 XIOs bit on first rung then the bit for output is latched. Then the next rung will be same Input with 1 XIC and 5 XIOs then the output is latched with a append rung beneath for unlatch the rung above for previous output. Repeat this step for all 6 outputs. I tried and cant get it. Only the 2 light wil come on and it stays on. You guys are awesome for your help. I need a lot of training whole new vocation for me.

This can be done easily by a counter that counts up once every time you press the Pb.

A example can be seen in this picture


/Victor

What software are you using? I can provide you with a Step7 version if you like when I get home this evening?

I tried the N7 Sequencer but can only get 2 of the 6 lights to come. I am on SLC 500/05.

RoyChozeh said:

I tried the N7 Sequencer but can only get 2 of the 6 lights to come. I am on SLC 500/05.

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You said you are not allowed to use Sequencer and if you are allowed then I have already shown you how to use it in post #3.If you have doubts about any part of that explanation you can ask and I will try to clear it up.It's a very simple program.

I want to learn how to use the SQO for myself for later cause it is alot quicker. I followed your steps and could get 2 light s to come on. I would press PB1 and it would cycle but only between 2 lights. It did cycle 6 times numerically but not through each light 1 time then to next light individually. Your info was very helpful. I am just new.Thanks Hazra

What numbers did you put in the N7 data file?
Did you put the same numbers as I did in till N7:6?

Also because you have 6 lights you can just copy my program exactly and only place 0 instead of 64 in N7:7.This change will cause all lights to turn off on 7th push of pushbutton and from 8th push the cycle will get started again.

My boss wont let me do it with sequencer. I am suppose to use latch and unlatch and a one shot.

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Why must it use latch and unlatch? That is a bad habbit, specially for motor outputs. Here is a way to do 3 lights with a one-shot and latches. Can you figure out how to add 3 more lights?

HINTS: Normally the fact that a PLC simulates a continuous process using non-continuous rung logic is not a problem. But when you use a one-shot, you have to be aware of the scan cycle, and what we used to call a "relay race". In an old real physical relay panel, all relays are connected all the time, so you had to be careful that your logic did not depend on which relay was (randomly) able to beat the others ON. In this PLC project, we can use "which rung goes on first" to solve the problem and lock out the others. In this situation, the order of the rungs DOES make a difference.

I am on a trainer. I am an intern for Control Engineering. I think my boss is trying to teach me something on how to do this. I am gonna try some of this you guys have shown and get back later. Many thanks to a novice. I am gonna try the N7 and latch example on here.

Personally I've never liked the SQO instruction, I learned it in College, and that is the only place I've ever used it. Former employer used them back in the 1990's, but customers were demanding a different method as the maintenance teams had trouble understanding the SQO (imaging 10-15 SQO instructions throughout the logic, and trying to keep them straight).

I personally will always make my own sequencing logic in an instance like this. Much easier to interpret and obvious as to what the code is doing. It requires more code, but sometimes the minimalistic logic just is not appropriate.

In this example, you could take the input signal using a one shot trigger a CTU instruction, as the counter increments the counter the .ACC value serves as "step number" in turn activate your lights as required.

Awesome got the SQO to work. Thanks Hazra. Now gonna try the latch. My boss dont want to use a SQO he says maintenance guys dont know that well enough to troubleshoot. Latch is next.