PB with NI-4070

[cyril.V]

 

I use an external sample clock to drive the acquisition of the PXI-4070.

The external clock is send to the TTL0 of the PXI chassis.

When I send 100 pulses with a 500hz frequency on TTL0, the acquisition is successful (I get 100 values).

But when I send 100 pulses with a 1000hz frequency on TTL0, I get only 50 values.

I set a 5 1/2 resolution in digits an the minimum aperture time.

The specifications of the PXI-4070 indicates the sample clock can be set to 3khz for this resolution.

So what's happened ?

I join my vi.

Thank you.

[Franck_C]

I have the same problem and not solution.

Please Mr NI can you help us

regards,

[Shea C]

cyril.V

Using the "niDMM Get Mesurement Period.vi" function you can see how the device settings that you have configured affect the reading rate that you can acheive. As you can see from the modified example that I included, the maximum reading rate that you can acheive when using the device as you have configured it is arround 900 Hz. This means that when using a 1 kHz clock that you would be missing some tirggers. The largest impact to the measurement period as you have it configured is the settling time. The default settling time is 1ms so reducing this would allow the DMM to measure at rates faster than 1 kHz and thus be able to use a 1 kHz trigger clock. Remember that the total number of samples that the DMM will aquire is Trigger Count x Sample Count. In your example you imply that you are taking 200 trigger counts and 100 sample counts for a total of 20k readings but you mention in your post that you are only sending 100 pulses. Even though no error is returned the aquisition is not completed until the board has aquired 20k readings. At that time the Aquisition state will move to a 1 or a 2 depending on whether or not you have retreived all the samples from the buffer.

I hope this helps!

Shea C

[cyril.V]

Thank you very much for your help.

The setting of the settling time solve my problem.