LabVIEW
Difference in t0 of waveform data occurs with 2 synchronised DAQ cards
Situation:
A PC with 2 NI-DAQ cards installed. A NI-6052E and a NI-6040E, the cards are linked to eachother on RTSI bus.
The cards are set up to be synchronised for continuous sampling.
Problem:
When i start reading data with DAQmx READ from both cards, i notice that starting from the first sample there
is a difference between t0 in the waveform data. This difference changes each time i run the software. This
difference is of a constant value with a single run.
Attempt to solve the problem:
-different methods of synchronization. Also used examples of Labview.
-different triggering methods for example: via RTSI using the dev1/ai/SampleTrigger to the other card;
-External triggering route
d through to trigger on both cards.
-Applying same trigger signal extrnal to both cards (Masterclock of dev2 synced to dev1)
Neither of these solutions help get rid of the difference in t0, or introduced other problems
Each run a check is performed if the dt of the waveform of one channel/card is equal to that of the other one, this is the case.
Questions:
1) Can someone explain this phenomena?
2) Is there a solution to it?
Regards
A PC with 2 NI-DAQ cards installed. A NI-6052E and a NI-6040E, the cards are linked to eachother on RTSI bus.
The cards are set up to be synchronised for continuous sampling.
Problem:
When i start reading data with DAQmx READ from both cards, i notice that starting from the first sample there
is a difference between t0 in the waveform data. This difference changes each time i run the software. This
difference is of a constant value with a single run.
Attempt to solve the problem:
-different methods of synchronization. Also used examples of Labview.
-different triggering methods for example: via RTSI using the dev1/ai/SampleTrigger to the other card;
-External triggering route
d through to trigger on both cards.
-Applying same trigger signal extrnal to both cards (Masterclock of dev2 synced to dev1)
Neither of these solutions help get rid of the difference in t0, or introduced other problems
Each run a check is performed if the dt of the waveform of one channel/card is equal to that of the other one, this is the case.
Questions:
1) Can someone explain this phenomena?
2) Is there a solution to it?
Regards
Answer is already found. The problem was caused by the Timestap that is linked to the waveform data. With the same signal applied to both cards we noticed that there was an exact match in signal form but a displacement in time. When setting the t0 of one signal equal to the other wenoticed the data was synchronised.
The origine why the time stamp differs still remains unclear to us
The origine why the time stamp differs still remains unclear to us
Carnivorus wrote:
> Answer is already found. The problem was caused by the Timestap that
> is linked to the waveform data. With the same signal applied to both
> cards we noticed that there was an exact match in signal form but a
> displacement in time. When setting the t0 of one signal equal to the
> other wenoticed the data was synchronised.
>
> The origine why the time stamp differs still remains unclear to us
The timestamp is added in software, not on the hardware. So the two Read
Waveform functions generate two different t0 timestamps as they execute
not really parallel. The data is generated synchronized though.
This is obviously a problem which can not be solved easily when using
the waveform datatype. Replacing one t0 with the other should be t
he
correct workaround.
Rolf Kalbermatter
> Answer is already found. The problem was caused by the Timestap that
> is linked to the waveform data. With the same signal applied to both
> cards we noticed that there was an exact match in signal form but a
> displacement in time. When setting the t0 of one signal equal to the
> other wenoticed the data was synchronised.
>
> The origine why the time stamp differs still remains unclear to us
The timestamp is added in software, not on the hardware. So the two Read
Waveform functions generate two different t0 timestamps as they execute
not really parallel. The data is generated synchronized though.
This is obviously a problem which can not be solved easily when using
the waveform datatype. Replacing one t0 with the other should be t
he
correct workaround.
Rolf Kalbermatter
