Is there a better way?

PhilipD · Oct 15, 2011

Hi all,

Here is a problem I had and have a solution for but I'm wondering is there is a more "eloquent" way.

I have 5 two position, maintained switches marked "ON" and "OFF". I need to know when any one (and only one) of the switches is on. Each switch is wired to its own input labeled Bypass Switch 1 through Bypass Switch 5.

I used this code to determine when only one switch is on.

Any suggestions?
Thanks.

L D[AR2P#0.0] · Oct 15, 2011

count := 0
if SW1 then count:=count+1;
if SW2 then count:=count+1;
if SW3 then count:=count+1;
if SW4 then count:=count+1;
if SW5 then count:=count+1;
if count = 1 then OTE=ON;

jstolaruk · Oct 15, 2011

Use it. Its simple and easily understood by others especially if you have a rung comment describing the intent.

daba · Oct 15, 2011

PhilipD said:
Hi all,

Here is a problem I had and have a solution for but I'm wondering is there is a more "eloquent" way.

I have 5 two position, maintained switches marked "ON" and "OFF". I need to know when any one (and only one) of the switches is on. Each switch is wired to its own input labeled Bypass Switch 1 through Bypass Switch 5.

I used this code to determine when only one switch is on.

Any suggestions?
Thanks.

You say switches 'ON', but your rung logic infers these are N/C switches, is that correct ?

If they are, that is an unusual configuration - consider the case you are running with NO bypass switches turned to the 'ON' position, and a wire comes loose off one of them. The logic would pick this up as the bypass switch being turned 'ON'.

Anyway, you asked if there was a "better way". Better for who/what - the processor, or the maintenance guy who has to debug it at some ungodly hour.....

The way you have it, the logic construct is simple, easy to understand, and is so much more "visual", when viewing the ladder, than the counting method proposed by L D[AR2,P#0.0]

PhilipD · Oct 15, 2011

daba said:
You say switches 'ON', but your rung logic infers these are N/C switches, is that correct ?

My mistake, that should read "OFF".

As to the meaning of better, this is really for me. Just want to see other methods.

Good eye!

TurpoUrpo · Oct 15, 2011

For arbitrary five bits, your's is good there is (that i know, for five, i would not count it). One can shave six xic's from it but that does not really matter.

But if bit count to check get's high, just count them like ld.

If all bits to check are in same word, then you can check if its in power of two (if looking for trues).

Gil47 · Oct 15, 2011

Not a better way just a different way

binary to decimal
11110 - 30
11101 - 29
11011 - 27
10111 - 23
01111 - 15

Then use the switch address, to an EQUals to, the decimal number, to set the output

Plcwill · Oct 15, 2011

PhilipD,

So, is your goal to see if any of the Bypass Switches are on and which one is it? If that is your goal, then something like this would work.



 

  X001   X002   X003   X004   X005      C4 

|-[ ]----[/]----[/]----[/]----[/]------(OUT)-| Bypass 1 on

 

  X001   X002   X003   X004   X005      C5

|-[/]----[ ]----[/]----[/]----[/]------(OUT)-| Bypass 2 on

 

  X001   X002   X003   X004   X005      C6

|-[ ]----[/]----[ ]----[/]----[/]------(OUT)-| Bypass 3 on

 

  X001   X002   X003   X004   X005      C7

|-[ ]----[/]----[/]----[ ]----[/]------(OUT)-| Bypass 4 on

 

  X001   X002   X003   X004   X005      C8

|-[ ]----[/]----[/]----[/]----[/]------(OUT)-| Bypass 5 on

Any changes in the states of the Bypass Switches would indicate which Bypass Switch was turned on or off.

BTW, are you using the Click PLC? I have this software installed on my laptop and if you need more help you can send it to me.

PhilipD · Oct 15, 2011

Plcwill said:
BTW, are you using the Click PLC? I have this software installed on my laptop and if you need more help you can send it to me.

Why, yes I am using a Click PLC. I installed it this morning. Thank you for your offer to help with the program but it appears to be working OK. Just a small program to control 5 air solenoids and 5 conveyors. I used the drum instruction to cycle from one to the other. Each conveyor has a bypass switch and that is the reason for the above code.

milldrone · Oct 16, 2011

Another not better just different way

Gil47 said:
Not a better way just a different way

binary to decimal
11110 - 30
11101 - 29
11011 - 27
10111 - 23
01111 - 15

Then use the switch address, to an EQUals to, the decimal number, to set the output

PhilipD said:
As to the meaning of better, this is really for me. Just want to see other methods.

The value in DS1 will change with each conveyor in bypass. Of course the logic must be placed in the ladder before you need to use it. The only time this would be better than your method would be if you needed to know the number of conveyors in bypass.

Manglemender · Oct 16, 2011

L D[AR2 said:
count := 0
if SW1 then count:=count+1;
if SW2 then count:=count+1;
if SW3 then count:=count+1;
if SW4 then count:=count+1;
if SW5 then count:=count+1;
if count = 1 then OTE=ON;

Interesting, LD [AR2, P#0.0] gave a much more efficient method but it seems to have been dismissed. It seems very logical to seasoned S5/S7 programmers, Is it so difficult to do in AB products?

Nick

PhilipD · Oct 16, 2011

Manglemender said:
Interesting, LD [AR2, P#0.0] gave a much more efficient method but it seems to have been dismissed. It seems very logical to seasoned S5/S7 programmers, Is it so difficult to do in AB products?

Nick

Not dismissed at all. I am studying all the posted examples and I am sure I will have the chance to use each of them at some point in the future.

This particular program was written for a Click PLC -- an Automation Direct product. Both AB and AD PLCs could implement this logic without to much difficulty.

I wish I had titled this thread "Is there another way?" The nuances of language can be misleading but that is being discussed in a different thread.

daba · Oct 16, 2011

Manglemender said:
Interesting, LD [AR2, P#0.0] gave a much more efficient method but it seems to have been dismissed. It seems very logical to seasoned S5/S7 programmers, Is it so difficult to do in AB products?

Nick

Nick, I didn't dismiss it either, but I'm not convinced that method is "more efficient" in any platform. Certainly in A-B it would not be, the simple bit instructions XICs and XIOs would execute way faster.

And of course, it is more "visible", because you can see the state of the inputs on each and every rung.

Mixing simple logic and math instructions may be just too much for the typical maint. tech, who may have to debug this when he's not 100% awake.

PS. No, not difficult,it is very easy to do the same in A-B products.

Plcwill · Oct 16, 2011

daba said:
Nick, I didn't dismiss it either, but I'm not convinced that method is "more efficient" in any platform. Certainly in A-B it would not be, the simple bit instructions XICs and XIOs would execute way faster.

And of course, it is more "visible", because you can see the state of the inputs on each and every rung.

Mixing simple logic and math instructions may be just too much for the typical maint. tech, who may have to debug this when he's not 100% awake.

PS. No, not difficult,it is very easy to do the same in A-B products.

I agree with this post 100%.

Not just the typical maint. tech, but everybody else that has to work on his system. That's why I believe the KISS method, which means less programming. That's why I shown my method in my post the way I did and is the same as Philip's thinking.

Peter Nachtwey · Oct 16, 2011

The OP has an acceptable but not optimal solution.

I have posted links many times to the bit twiddling web pages.
Why do I bother?
Oh, please, some one provide an optimal answer.
Sometimes I think this forum is a waste of time if no one learns from the past.

Is there a better way?

PhilipD

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