480 ms cycle time using ET 200 SP, 8ch x AIxI, over Profibus

Extremely Slow Response on ET 200 SP, 8xI (6ES7 134-6GF00-0AA1) and 8xU (6ES7 134-6FF00-0AA1) over profibus

1. we are using a legacy antiquated control system to communicate over profibus to 4 x ET 200 SP io systems.

2. 3 of these io systems has onnly digital io, while the the 3rd of the 4 io systems has analogue io, which is around 100 meters away from the master, in cable length. 

3. profibus speed set at 3 MBits per sec, as per proficentre specification 

4. the cycle time achieved is around 480 ms, which is reason for this post

5. the analogue io configurable settings in the GSD allows for a "interference suppression frequency" to be set. the dafault is set at 50 Hz (60 ms)

6. with an 8 ch AI x I module, it seems to imply that 8ch x 60 ms ( interference suppression freq) = 480 ms is the reason we are achieving this cycle time

Query: can someone please clarify from experience what this interference suppression freq means, and if it is the cause of the extremely poor cycle time?

note: not so easy to test with a live running plant, it means plant downtime, which is extremely difficult

Hi there,

to put it short: You're right about the interference suppression frequency causing the cycle time of the module (at least the largest part of it).

In detail:
The module is a BA variant. To my knowledge these BA modules work sequentially, to they get each channel one after the other, and the sum is the total cycle time of the module. See here for an explanation about this: https://support.industry.siemens.com/cs/de/en/view/67989094/61580456203

Unfortunately I could not find a statement about the sequential working in the technical data (https://support.industry.siemens.com/cs/de/en/view/109475183/76346357899), but perhaps I just missed it.

Information about the interference suppression frequency and how it should be set can be found here: https://support.industry.siemens.com/cs/de/en/view/67989094/61580316171

I'm a little lazy right now (), so I just link to another thread with basically the same issue, where I answered this some time ago. My answer back then also applies here: https://support.industry.siemens.com/forum/de/en/posts/6es7534-7qe00-0ab0-update-of-signal/269461/?page=0&pageSize=10 

Regards,
daviso

Hi,

as already mentioned the BA modules do work sequentially, so the cycle time of the module is the total of all channels + some side effects + communication.

If you do not use all channels, you can simply disable unsued channels in hw config. This is probably the most "easy improvement". But if you need all channels, this is not possible of course.

The suppression frequency does effect the conversion time (cycle time) per channel directly.
In general, the voltage suppression for interference frequency should be configured to the frequency of the used supply voltage. If this parameter was configured differently, this "can" have negative impacts to the quality of the measurements.
But you can simply try to change the suppression to 4800Hz. This will result in a much lower conversion time per channel and in a much lower cycle time of the module.
If the quality of the measurement is still fine for your process requirements, this could be used alternatively.

regards

sancruz