connecting a schneider quantum to a pair of parent and child Modicon micros

hi

If anyone is good enough to answer the question below please reply in a manner befitting an idiot

I have connected 2 modicon micros in a parent/child configuration to control a trimming system which removes the external weld bead on a newly formed tube

the problem is that a tube is made by welding coils of strip together, and these "cross welds" can break the trimming tools as they pass through the trimming system, and so the tools have to be disengaged for a second or 2, every 3 mins or so

in order to track the "cross weld" a blue sticker is placed next to it, and a colour sensor registers its arrival in the mill with a completely seperate schneider quantum, while an encoder/pulse wheel tracks its position, sending the pulses to a high speed counter in the quantum

what i need to do is get three seperate signals (events) from this counter to the modicon micros

a collegue at work tried to explain a solution to me, but my eyes just glazed over (I could see his lips moving but that was about it)

The solution I was given consists of two networks (attached) below is my understanding hopefully you can fill in the blanks

NETWORK 1 JPEG

The contact connected to the optical sensor closes as the blue sticker passes by, which closes the internal contact X and so latches itself. This in turn will enable the counter (not sure what that means in any detail)

I'm unsure what the "P" contact on the fourth rung is or does

Its connected to a counter register associated with the high speed counter which contains an exclusive OR gate which I think is used to reset the counter?????


NETWORK 2 JPEG

I was told the three internal registers are subtraction blocks used as comparison blocks????
These, store the number of pulses relevant to the set distances,

The fact that the output connection is in the middle of the block, and is connected to the top there will be an output when the counter is greater or equal the quantity in the register?????

Finally, after the last event the normally closed Y contact found in the first network opens and the first latch is lost
The cycle begins again, when the next blue sticker passes the sensor

Hope all this made sense

If you can shed some light on the above or need any more information, you can contact me at [email protected]


any help is very much apprieciated

cheers

Ash

Let's take the easy stuff first...

MatAsh said:

I'm unsure what the "P" contact on the fourth rung is or does

Click to expand...

That simply indicate a differential contact that will turn on for 1 scan at the transition from OFF to ON (See Phil's explanation HERE). In your logic, it's used to perform the XOR mask ONCE each time 'X' turns ON. "P" meaning "pulse"...

The rest is only 'part' of a program, and I'm not familiar with Modicon, so we'll wait for others...

beerchug

-Eric

The 'P' instruction is a positive edge one shot, which is driving the XOR block to set the count to zero as soon as the 'X' output is energized.

That is a code fragment to be sure. It will definately do something. It's hard to say exactly what though from the snippet you provided.

It seems you would just want to
1) Reset the counter on Blue Mark (that seems done),
2) Turn off / retract cutter
3) At some fixed product length later, re-enable cutter.

That can be accomplished by the first network, and then a simple compare against the counter to see if the weld bead has passed.

You would have to calibrate the counter (encoder) to get a decent number of counts to certify that the weld bead has passed though.

Modicon 984 Ladder Logic

The networks you have correspond to your written description. However, you have a problem with your XOR block.

The P contact is a "Positive" edge sensing contact that is only true (closed) for 1 scan after the input transitions from open to closed.

The XOR block is one method that is used to set a series of coils or a holding register equal to zero.

The subtract block is often used for comparisions due to it's three possible outputs (<, =, and >) which you are combining in parallel to create your "> or =" function.

Your network is trying to have3x1 XORed with itself, this is not possible. A 3x register is a read only input register. You may have to use a block move (BLKM) to transfer your 3x input register to a 4x holding register and then use that 4x register in your comparisons.

Where is your 3x1 coming from? Is this a high speed counter module in the Quantum? Can you reset the module rather than XORing the result?

Your network is trying to have3x1 XORed with itself, this is not possible. A 3x register is a read only input register. You may have to use a block move (BLKM) to transfer your 3x input register to a 4x holding register and then use that 4x register in your comparisons.

I'm not quite sure what you mean by this jim but there was reference to 4001=preset (listed but not shown on the original sketch)

and each subtraction block had a 4000 number as well as 3001

4002=(subtraction block 1 I/D trim off)
4003=(subtraction block 2 O/D trim off)
4003=(subtraction block 3 both back on)

which I have forgot to put on the diagram

Where is your 3x1 coming from? Is this a high speed counter module in the Quantum? Can you reset the module rather than XORing the result?

the eyes are beginning to glaze over again jim

I think the answer is yes my 3x1 are coming from a high speed counter in the Quantum and I'm sure my colleague said that the XORing was not the only way of getting zero but was a fancy way, so you probably can reset the module but I haven't got a a clue how

hope this helps

Ash

There are two types of registers. 3x (your 3001) which are inputs from High Speed Counters or analog devices, your program cannot modify a 3x register. 4x holding registers are able to be modified by the program and are often used to hold "adjustable" preset values (hence your 4001=preset).

fixed = 100, and adjustable = holding register 4001

  |----|              |----|

  |3001|              |3001|

  |    |              |    |

  |#100|              |4001|

  |SUB |              |SUB |

  |4100|              |4100|

  |----|              |----|

One possible network to zero and then read your HSC is:
where 4x equals the first configuration register of your module, check your "traffic cop" for the exact value
The first ADD sets the value 0 into the preset register for channel 1
The second ADD puts the HSC into Load Values mode (515Dec = 203Hex)
The third ADD puts the HSC back into Read Values mode (770Dec= 302Hex)

 |                |              |

 |-----|          |-----|        |-----|

 | #0  |          |#515 |        |#770 |

 | #0  |          | #0  |        | #0  |

 | ADD |          | ADD |        | ADD |

 | 4x+1|          | 4x  |        | 4x  |

 |-----|          |-----|        |-----|