ADC Linearity Evaluation using a 6571 for sampling through capture waveform and a 6368 to source an ramp waveform

[Caloi]

Hi everyone, I'm going around in circles with this, I'm a little inexperience on using the DAQmx. To give you an overview, we are trying to get the linearirty evaulated on a device, we have a 6368 DAQmx that is connected to “PinA” where the 6368 generate a voltage ramp for a period of time. The 6571 is then being used on a couple of pins and to also capture a waveform/serial data (burst on some pins, capture on one). The sample being returned is the equivalent code from of the ADC.

I’m currently able to generate a ramp sequentially using a 6368 and 6571. And compute the INL/DNL of the ADC but the way this works is I'm just trying the ramp 6368 is not fully synchronized with the 6571 Below is the diagram for my current approach and code.

Now my current implementation shows that I'm generating a ramp using a 6368 while sampling with the 6571. The problem with this is they are not fully synchronized. My capture waveform setting and digital pattern is as shown below:

As you can see on the probe window above, I can get 4 codes (samples) per iteration that is going from minimum to maximum voltage. but the readings are not so accurate, I'm assuming this is because the sampling didn't really start at the beginning of the ramp, and there's a lot of missing codes because the sampling on the ramp by the 6571 is not "timely".

Is there a way for me to have the 6368 ramps at exactly every step of the ADC, say for example every 1.85mV from 0V to 4V?

[santo_13]

You can synchronize 6571 and 6368 in a few ways.

1. Loop back one of the 6571 channels to 6368 PFI files, send a pulse from 6571 whenever you need the next ramp level, configure 6368 to use the PFI line as a sample clock
2. Configure a start trigger export from 6571 and configure 6368 to start the task on this exported trigger, ensure the 6368 waveform is precisely timed to match the 6571 execution as the synchronization is only at the start

Depending on the bitness of your ADC, 6368 is typically inadequate for DC tests due to its accuracy specifications.

[Caloi]

Hi Santosh,

I'm trying to do the 2nd option you mentioned. But it says the specified property is not supported by the device to the task. I'm trying to create a trigger signal line on the 3rd photo. Am I missing something?

Thanks.

Regards,

Carlo