double coil syndrome

i would like to know what is meant by double coil syndrome in PLCs.

Double coil = the same output (coil) used more than once in a prog..

|---]b3/0[----------------------(O:2/0)----|

|                                          |

|---]b3/1[----------------------(O:2/0)----|

What happens you decide???????????????



Jezz

Doctors hate to have to admit it when they don't know evrything about an illness. When faced with that situation, they use the term 'syndrome', which can be considered a code phrase for 'haven't got a clue'.

Double coil syndrome is the doubt and uncertainty in the troubleshooter's brain caused by the programmer applying the same address to two (or more) coil instructions in the same PLC program. It arises from looking at a rung of ladder logic where the conditions are all true, but the coil shows false or where the conditions evaluate false, but the coils shows true.

Symptoms include cursing, forehead denting, calling the programmer rude names, questioning the legitimacy of the programmer's ancestry.

There is no cure, but the severity of an attack of DCS can be reduced by applying a generous measure of common sense to the writing of ladder logic, and by a thorough understanding that a ladder logic program in a PLC operates differently than a Visual Basic or C program in a PC.

Steve Bailey said:

Double coil syndrome is the doubt and uncertainty in the troubleshooter's brain caused by the programmer applying the same address to two (or more) coil instructions in the same PLC program. It arises from looking at a rung of ladder logic where the conditions are all true, but the coil shows false or where the conditions evaluate false, but the coils shows true.

Click to expand...

Simatic Step5 shows both ok. I don't know Step7. Many other PLCs shows as Steve told.

Steve Bailey said:

Doctors hate to have to admit it when they don't know evrything about an illness. When faced with that situation, they use the term 'syndrome', which can be considered a code phrase for 'haven't got a clue'.

Double coil syndrome is the doubt and uncertainty in the troubleshooter's brain caused by the programmer applying the same address to two (or more) coil instructions in the same PLC program. It arises from looking at a rung of ladder logic where the conditions are all true, but the coil shows false or where the conditions evaluate false, but the coils shows true.

Symptoms include cursing, forehead denting, calling the programmer rude names, questioning the legitimacy of the programmer's ancestry.

There is no cure, but the severity of an attack of DCS can be reduced by applying a generous measure of common sense to the writing of ladder logic, and by a thorough understanding that a ladder logic program in a PLC operates differently than a Visual Basic or C program in a PC.

Click to expand...

ROFL Steve, don't think that anyone here hasn't seen that before.

* ON TOPIC *

Can't speak for all PLC makes, though the last repeated "Coil" rung dictates the state of the output.

You can make double coil if you want in SFC

Normally, we can not make double coil in ladder program ..
but I recommend if you want to make some program in sequence
with the same output(for example out2/0 of Ab or Y0 of Mitsu fx
work more than 2 times , you can use more internal relays (B3/0 ..of Ab or m0...m1 in Mitsu to energize out 2/0 or...yo )

However,if you want to use really the same such output (not internal relay)2 or more out2/0...or y0 more than one coil
you can use Stl,Grafcet in some plc brand or Sequencial fungtion chart (SFC in mitsu)as well in difference state

Platootod

******Double Coil Syndrome --> stay away!!
============================================

Have you heard the term "double coil" before? Are you confused by its
meaning? Well perhaps you're not alone on the subject. And if you've
never heard of it before... it may actually be a good thing. Let's
check out the *disease* together.

The double coil syndrome occurs when we use the same output coil more
than once in our ladder program. What... we can only use the same
output coil once in a program? Well, yes that's true. Let's see why:

Consider this simple example. We have two toggle switches. If either
of them turn on, then a motor will turn on. Simple. We just create a
two line ladder diagram that looks like this:

0001 0500
--| |-----------( )---

0002 0500
--| |-----------( )---

So, if either input 0001 or 0002 physically turn on, then output 0500
will turn on and our motor will spin. OK. Let's move on to another
topic then... but wait. It won't work. Huh?? That's right. It won't
work they way we designed it. Why? Because of DOUBLE COIL SYNDROME.

The dreaded programming disease appears here because we have used the
same output coil (0500) twice in the same program on two seperate
rungs. Care to guess what the symptoms will be? (Sometimes they're
hard to diagnose)

The symptom would be turning on/off toggle switch 0001 but the motor
0500 never turns on. But if we turn on/off 0002 the motor 0500 also
turns on/off. This tells us the motor is good. More checking reveals
that the PLC input card is working just fine. So, back to the program.

The cause of the disease is the way our PLC scans the program.
Remember that it scans from left to right, top to bottom. Watch this.

0001 0500
--|a |-----------(b )---

0002 0500
--|c |-----------(d )---

Initially:
a and c are physically off. So, b and d are also off.
Step through the scan:
1-- We turn on toggle switch 0001 so a is now on.
2-- Since a is ON, b (0500) will turn on.
3-- c is still physically off, so d (0500) is also off.
See!! The last thing we said was that 0500 would be off. So, when the
PLC goes to update the outputs, it's going to leave 0500 OFF!!

How about this situation:
Initially, a and c are physically off. So, b and d are also off.
Now we turn on toggle switch 0002 so c is now on.
Step through the scan:
1-- a is off so b (0500) is off.
2-- c is on so d (0500) will turn ON.
See!! The last thing we said was that 0500 would be ON. So, when the
PLC goes to update the outputs, it's going to turn 0500 ON!!

If you've followed along, you'll notice that -- regardless of whether
toggle switch 0001 is on or off, motor output 0500 reacts only to the
state (on/off) of toggle switch 0002 --. If 0002 is on, 0500 is on. If
0002 is off, 0500 is off. It doesn't matter what the status of toggle
switch switch 0001 is. 0001 is pretty much ignored.

How do we "cure" this disease and eliminate the syndrome?? Simple.
Just use an OR ladder. After all, we want the motor to turn on if
toggle switch 0001 *OR* 0002 turns on. Here's the solution:

0001 0500
--| |-----------( )---
|
0002 |
--| |----|

Now, if switch 0001 OR 0002 turn on, 0500 will turn on. Double Coil
Syndrome has been cured.
Vaccinate yourself now and you'll never get the disease!!
Just for reference about the only time the same output coil can safely
be used is within subroutines and transitional(jump, etc) blocks.

***Taken from Phil's Newsletter***

coil is misleading

In AllenBradley, you can make a coil type output instruction
to a 'bit within a word'

SO, you might have a program that says

-----------MOV N11:0 N7:0

and later
N7:0/2
--------------- ( ) ---

and wonder why the value of N7:0 is sometimes off by 4.

Whith AB-plc I do this kind of rungs for the small vertical view-area only.

 

                                                  out x

---] [-------] [-------] [-------] [------] [------( )---

  out x                                           out x

---] [-------] [-----------------------------------( )---

Above, it is for the view-tech so. they are in the same view, if
there are many of contacts in serially. If outputs write to process image after program scan, this is quite ok.

F.e. Simatic Step5 you can see everything as they are in the rung.
Step5 shows RLOs as they are in the view.
Not the end of the program scan, as in many other PLCs.

if there are many of contacts in serially.



huh????

harryg said:

huh????

Click to expand...

Harry, sorry my english, but what are you huhhing ?
br. Seppo

seppoalanen said:

Harry, sorry my english,

Click to expand...

Seppo

there is no need to apologise for your English, one glance at your country flag is enough to know that English is not your first language.

I am sure 99.9% of people here knew what you were trying to say.

HarryG, I found your comment rather rude! shutit

Paul

Thank you man i appreciate it

old threads turned up by search provide answers for new members.
Awesome...

jdbrandt said:

In AllenBradley, you can make a coil type output instruction
to a 'bit within a word'

SO, you might have a program that says

-----------MOV N11:0 N7:0

and later
N7:0/2
--------------- ( ) ---

and wonder why the value of N7:0 is sometimes off by 4.

Click to expand...

Lancie

Why would the value be of by 4? What is the value of N11:0?