[etherlab-users] Duplicated values bug, when measuring external frequency generator signal, with beckhoff EL3064 &EL3062 slaves and etherlab

[Lazaros Penteridis]

Hello,

I have etherlab(the latest versions of all the components) installed, under
a 3.4.69-rt85 linux kernel, in 3 different computers, which I connected
with beckhoff EL3064 or EL3062 slave, via ethernet using the beckhoff
EK1100 coupler.

Using this set up, I measure, as input to the EL3064 or EL3062 slaves, a
sine wave signal with 40ms period, produced from a frequency generator. I
performed this experiment using different sampling frequencies and I notice
in the measured signals that some sample values are duplicated(two adjacent
samples have the same value). The frequency that this duplicating error
occurs varies relative to the sampling frequency that I choose for the
slaves(the errors occur more rarely the higher the sampling period goes
until the point that, with 1300us sampling period, I get a mean error
occurrence frequency of approximately 1 per day.

Bellow you will find attached an image showing these duplications, for a
signal that was measured with sampling period of 1000us. For the logging of
the measured data both test manager scope and dls from igh where used, with
no difference in the results of course.

The frequency of the duplications is not related to which of the 3
computers is being used, under the same sampling frequency, so I'm assuming
it's not related to the computational power and the performance of my
real-time systems.

Could you suggest what the reason for these duplications might be(beckhoff
hardware problem, software bug) and if there is something I could do to get
rid of it?

Thank you in advance,
Lazaros
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