High speed input over profinet

[rQx]

Hi,

I have a setup of one master s7-1200 - three slaves s7-1200

On each of the slaves there is a HSC on a motor for positioning. It generates around 300-400 pulses per second, can this be transfered over profinet with I-device. Or is it to slow? The distance between the master/slave is within 20m.

Can it be done if the slaves were to have a Siemens LOGO also?

I'm in the develop phase so I investigate what path to go

/Tim

 

[JesperMP]

It depends on what the application is.
I assume that you are transfering the count value from the HSC module, not the raw impulses.
I think you should be able to achieve a Profinet update time of 2ms without much problems. If that is fast enough is up to the application.
For very fast applications you may need Profinet IRT instead of 'just' Profinet RT. I dont think S7-1200 supports Profinet IRT.
To find out the actual update time of the values you need to take everything into account. Also the CPU update time of both Controller and I-Device PLCs, and the update rate of the HSC module.

 

[rQx]

It depends on what the application is.
I assume that you are transfering the count value from the HSC module, not the raw impulses.
I think you should be able to achieve a Profinet update time of 2ms without much problems. If that is fast enough is up to the application.
For very fast applications you may need Profinet IRT instead of 'just' Profinet RT. I dont think S7-1200 supports Profinet IRT.
To find out the actual update time of the values you need to take everything into account. Also the CPU update time of both Controller and I-Device PLCs, and the update rate of the HSC module.

I was thinking of the raw impulses, having the slaves work as decentralized I/Os. Maybe et200SP with high speed input module is better? I can also just have it hardwired to the master PLC, that may be a easier way of doing it

 

[JesperMP]

Maybe et200SP with high speed input module is better?

If the slave S7-1200 doesnt do anything autonomously, then they are just Profinet IM devices, only slightly more expensive than regular IM devices.
At up to 400 pulses per second, I would not go for reading the raw pulses in the PLC program. Also, are you using an encoder to generate the impulses ?
If so, encoders usually have A and B channels. These channels switch in a certain order to indicate the direction.
A dedicated counter card can be setup to connect to the A and B channels and automatically count up or down.
So I would go for a distributed ET200SP with counter module (not high speed inputs).

 

[JesperMP]

If you go for the high speed inputs:
At 400 impulses persond, and assuming symmetrical on and off periods (!), you need to sample the inputs every 1 ms. And that must be consistently. Otherwise you will skip impulses.
I think that is too much for an S7-1200.

 

[rQx]

If the slave S7-1200 doesnt do anything autonomously, then they are just Profinet IM devices, only slightly more expensive than regular IM devices.
At up to 400 pulses per second, I would not go for reading the raw pulses in the PLC program. Also, are you using an encoder to generate the impulses ?
If so, encoders usually have A and B channels. These channels switch in a certain order to indicate the direction.
A dedicated counter card can be setup to connect to the A and B channels and automatically count up or down.
So I would go for a distributed ET200SP with counter module (not high speed inputs).

Yes, but we only use one of the channels. The alignment is not "that" critical on the mm and we only count in one direction. The other direction is just to get back to home position. I will look into the counter card, or possibly manage the counting in the slave (if I go for the s7-1200), thanks alot for your time and help

 

[Tinine]

Disclaimer: I know very little regarding PLCs but I did a quick search for "quadrature encoder to Profibus" and a module came up. Although it was shown as an option for a motor controller, it appeared to be capable of standalone operation. Aren't you dealing with 5v signal levels?


It was like 700+ bucks, mind.


Craig

 

[Peter Nachtwey]

400 counts per second is slow. That is only 4 counts per 10 m/s interrupt. Some times you will get 3 counts, mostly 4 counts and some times 5 counts per 10 ms interrupt. This makes it hard to calculate a speed that doesn't jump around a lot.

 

[JesperMP]

Disclaimer: I know very little regarding PLCs but I did a quick search for "quadrature encoder to Profibus" and a module came up. Although it was shown as an option for a motor controller, it appeared to be capable of standalone operation. Aren't you dealing with 5v signal levels?

S7-1200 only support Profibus by adding a CM1243-5 module. It gets complicated.

Also, there are no counter cards for the S7-1200.

I think a small S7-1510SP CPU plus one or more counter cards would be a better solution than trying to make a cludge with one or several S7-1200 PLCs.