High trigger accuracy with Siemens 313C PLC??

For a vision application I need to trigger 3 camera inputs with a PLC to make 3 pictures of each bottle on a conveyor.

The capacity is 8000 bottles/h



Depending on weather the bottle is good or bad, an action needs to be taken.



Each trigger must come on a different moment.

The PLC must give a trigger to the cameras each 450ms, with a accuracy of 5ms.

The trigger signal must stay on for about 100ms.

The position of the bottles on the conveyor is monitor with an encoder.



I have to use a 313C PLC of Siemens.



My questions:

how should I do this, en how can I be sure that my PLC outputs are triggers within the given accuracy of 5ms?

Are there some SFB?

Can I use OB40?



Thanks for your reply

You're not going to get 5 ms accuracy out of a 300 Series CPU on its own - end of story!

If your budget will stretch to it you'll find a perfect solution in the High Speed Boolean processor, FM352-5. It may also be possible with the FM352 cam controller module, but since I haven't used it, I can't be sure of that. I believe S7Guy has used it though, so perhaps he can say whether it will solve your problem or not. If you do decide to (or have to) go the FM352-5 route, be warned the learning curve is steeper than the North Face of the Eiger, however, since I've already been down this painful route, if you do a search for "FM352-5" here, you'll find most of the info you need, if not, feel free to come back and ask.

Edit:

PS, I used the FM352-5 for triggering optical SCRs to fire multiple capacitor banks, the accuracy in the ms area is ~10 µs or better.

How do you know the position of the bottles ? I suppose you have an encoder which is synchronised with the conveyor so you know where the bottle are and when the camere must be triggered?

Some points to think of:
- What is the cycle time of your PLC-program? If it's very small ( cycle time < 5 ms) then you could cyclically read the encoder and generate the pulses.
- How do you trigger the camera ( hardware )? Transistor output + optocoupler? What is the delay time and accurency?

I don't think there much you can do with the integrated counting/comparison functions as you need three triggers.

Succes !

Even in the 313C you have specific OB's that are called cyclic (with a regular interval time) the program inside the O (OB35 for instance shouldend require more time then the interval time for the next execution of the OB.
In the hardware configuration of the cpu you can change the interval time for OB 35. I'm not quit sure how this ffect the operation of the CPU.

Sinds you are required to use a 313c you can give it a try.

Regards,
Jurgen

I don't have a handbook for the 313C to hand, so I can't check it, but to the best of my knowledge, in the 300 Series (even up to the 317) the shortest time interval you can specify for Timers etc. is 10ms. I wouldn't be surprised to learn that OB35 won't even go down this far and may stop at 50ms.

Based purely on cycle time, RMA is right.

But JvdV might have a point, since Leonardo mentioned:

Leonardo said:

The PLC must give a trigger to the cameras each 450ms, with a accuracy of 5ms.

The trigger signal must stay on for about 100ms.

Click to expand...

One could set the interrupt time to 450ms to call OB35 and start a 100ms timer from within OB35.

RMA: I think your solution will work, but such a FM352-5 is not cheap, and as you also mentioned, the engineering time will increase too.

Any other solution(s)?

Maybe the S7Guy can help…..



Flukie: yes, I will use an encoder to know the position of the bottles and to know when the camera must be triggered.

I don ‘t know the exact cycle time of my PLC program, but I don ‘t want to rely on it….



Kataeb and JvdV and Sparkz: I could use a puls output or timed OB if the exact trigger frequency is know, but in my case it ‘s not exactly 450ms, but depends on the position of the bottles (measured by the encoder).

(Maybe this was not clear in my question)

I've not used a 313C so I can't advise if the onboard functions will help or not, but, I have some more general questions:

1. Why do you have to use a 313C ?

2. What is your deadline for having a working system ?

is the encoder connected to the 313C digital inputs?

because you depend on the position of the bottles, you can:
1. use a pulse counter to count the encoder pulses and determine 3 position values to trigger the camera (maybe using ob35 and immediate inputs and outputs on the plc)
2. or better as you have 2.22 bottles every second, install fiber optic (or photoelectric) sensors at 3 position of the bottle, and connect the signals directly to the camera