Any PLC

[Terry Woods]

Well, ya know... if you spend all of your time following all links that come your way... you're likely to end-up being anywhere but where you wanted to be! Even if it was my own thread obscured by an apparently random post-number! That is the nature of the Net!

 

[Peter Nachtwey]

Why is this so hard?

I asked 5 people to work out a one button toggle in ST and gave them one half hour and still no one figured it out. There were four maintenance guys and a salesman and strangely the salesman got closest because he used a built in toggle function.

Light0:=Light0 xor ( PB0 and not LastPB0 );
LastPB0:=PB0;

I had already written this on the white board.

Light:= PB and not LastPB;
LastPB:=PB;

PLCs were not invented yet when I went to high school. Still we learned Boolean logic and DeMorgan’s theorems. This is early 1800's knowledge.

Now back to the original topic. PLCs are just things. They are tools that become obsolete and will be replaced by newer technologies in the future. Boolean logic and DeMorgan's theorems are forever. Learn them and you will be able to solve your problems with whatever tool you use.

 

[darrenj]

I never thought much about using a one button start stop..until about 3 or 4 weeks ago..i then had an apliaction for one..I thought about it and 10 mins later its tried, tested and true..

However asking me to write it in ST would be a challenge..I must look at this ST more..it seems to be the way of things..

 

[Peter Nachtwey]

No, learn the basics. Learn the knowledge that is forever.

I never thought much about using a one button start stop..until about 3 or 4 weeks ago..i then had an apliaction for one..I thought about it and 10 mins later its tried, tested and true..

Good for you!

However asking me to write it in ST would be a challenge..I must look at this ST more..it seems to be the way of things..

ST is also just the latest one of the latest programming fads. Learn Boolean logic and DeMorgan's theorems. Learning ST is good, but this knowledge is only useful while 61131-3 is the current fad.

I am hoping that every sees the difference between tools and knowledge. PLCs, HMIs and motion controllers are just tools.
They will change. The physics, logic and math are forever.

 

[darrenj]

Its been quite a few years but we did do boolean in school..i am sure i have forgotten way more than i learned since then..but..

 

[Terry Woods]

"Why is this so hard?"

It's NOT hard!

That is the point I've been trying to make for these last few years!

It's simply a matter of "humanizing" the concept!

If I press a button that controls a light and before pressing the button the light is off, then the INTENT is to turn the light on. However, if, before pressing the button the light is on, then the INTENT is to turn the light off!

So, in terms of controlling the light, it is simply a matter of KNOWING what the state of the light is WHEN/AS I press the button! THEN... after changing the state of the light based on the previous state, I have to remember that I have already pressED the button and am now HOLDING the button!

Sure... after having pressED the button I'm still pressING the button, however, after that point where the program first detected that the button was pressED, from that point on, I'm pressING (HOLDING) the button!

The KEY is that the state of the light changes only when the button is first pressED!

Once the button is pressED, and the state of the light has been changed, either ON or OFF, you NEED TO KNOW that the button WAS pressED[/ED]!

From that point on, until the button is released, the state of the light can not be changed!

After changing the state of the light based on the previous state... the state of the light no longer changes as long as the button WAS pressed.

The button must be released, thus negating "WAS", in order to be able to change the state of the light again!

 

[Fox]

Hi

When i've suggested to use a pulsed function I was thinking of very usefull functions like ALTP. This is an alternate pulsed function used like this:

LOAD INPUT X
ALTP OUTPUT Y
​

so, each time we activate input X output Y will toggle.
Japanese PLCs have lots of these kind of functions and they are very usefull.

 

[Terry Woods]

Hmmm...

Will that work in a low-level AB?

 

[504bloke]

Hmmm...

Will that work in a low-level AB?

Only if the low level AB has the instruction ALTP or similar ?

 

[Terry Woods]

DUH.... do ya think?

I don't.

 

[Thomas Sullens]

The physics, logic and math are forever.

How can you say this? OUR math is not forever because it doesn`t come out! What we use is close enough for what we do, but it not dead nuts on look at pi. Now if the Romans hadn`t of killed him. He might have figured the rest of it out! But that`s not the case???
I`m only kidding i`m sure there is math that really does come out, but then i don`t understand the math that doesn`t.oh well! Why do we still 3.14xxxxxxxxx anyway? Some use 22/7 what ever that is, says it gets closer?? I thik i`ve read to many post today. Uh Oh! now my spelling going to pot also and i don`t even drink, which has not always been the case.
:site:

 

[Terry Woods]

The question of math is very interesting...

It used to be that we only dealt in integers...

Then we started dealing in other types of numbers...

And then others...

I saw (not literally) the progression go from Integers (Cuniform), to Algebra (based on the Arabic Number System - you know, like Arab, like Moslem, like Islam... The Arab World used to be THE Intellectual World - they invented the concept of zero, while the Western World was sitting comfortably in the Dark Ages!), to Calculus, to...

I've always known that we don't have the all-encompassing method inhand.

We've gone from the line, to a curve, to a curve through time... what is next?

We definitely don't know that single, all-encompassing, math system that covers all bases.

However, Peter's point is valid! As far as we can tell, physics, logic, and math, are the rules that govern, and perpetuate our existence! It's simply a matter of (easier said than done) finding that all-encompassing math method!