sync sampleclock over pfi possible? 2 devices.

[dannyz]

Hi,

is it possible to sync 2 devices ( 2 x USB 6251) with a shared sampleclock?

I would like to to use the pfi pins for shared samplesclock by connecting them??? ( not over RTSI!! just a port to port connection).


greetings

dannyz

see the vi below!

[DanielHermyt]

Hi dennyz,

to answer your questions.

1. You can use your PFI-ports for triggering. Please have a look at "Cont Acq&Graph Voltage-Ext Clk.vi" or "Cont Acq&Graph Voltage-Ext Clk-Dig Start.vi" that are shipped with your LabVIEW installation. It doesn't matter where the triggering signal comes from.

2. If you generate a trigger signal from one device and use this on both, you use the same time base. You cannot synchronize the clocks on both devices, but you can generate a trigger for both.

3. As you don't need the for loop in your implementation, as you mentioned with "Indexarray", you should use this. Try to use as less loops as possible.

4. As you read waveform data, you don't need to create an extra timestamp. When you trigger the measurement with one trigger signal, you have the same time base.

[dannyz]

Hi oyster,

thank you very much for answering!!!
I want to sample Data of 5 device at about 1kHz.

1) So do you think the hardwaretrigger is necessary or is the software fast enough??

I tried synchronising over the PFI and it did work, but i fear that the digital GROUND of each device could influence the card and also come to floating masses.

2) So do i need a galvanic separation, like opto-electronic couplers ??

thank you very much for your helpfull answers!

greetings

dannyz

[DanielHermyt]

Hi Dennyz,

to answer your questions:

1) You can use both, the speed should be enough. As the software triggering depends on the ressources of the Operating System, Hardware Triggering is more stable.

2) No, you don't need galvanic separation.

[dannyz]

Hi Oyster,

thank you very much!

You are right, on one PC the Softwaretrigger (just DAQStart) for an analoge Output takes up to 8 ms timedelay. I will trigger other Devices over bnc!

Thank you!

greetings

Daniel

[dannyz]

Hello,

i have a new problem! I have now syncronized all devices over PFI,  i exported the AI Sample clock to the PFI line. When i look at the scope there the sampleclock is 1khz but the duty cycle is only 50 ns ( 20khz).

How can i change the pulse to a with of 100 us, the 50 ns Puls is to short, so that sampling is working but it is not stable and it does reach only 1,5 Volts!

I use the Exportvi, see the vi below.


thank you!!!!

dannyz

[DanielHermyt]

Hi dannyz,

the sample clock is the clock that is connected to your device, it is only an internal routing from the samplclock input to the PFI pins.
You don't need to use external counters.