Time delay between acquiring analog voltage signals and outputting digital pulse for trigger

[JMark111]

Hello!

I am currently using the PCI-6034E DAQ, interfacing with a BNC-2110 block. We
have two piezoelectric patches fluttering and generating AC voltages, which
are subsequently read by a user-written program in Labview through two analog
inputs in the BNC-2110 block. When activated through the program, the raw
voltages are written to a measurement file.

Along with the voltages, we are sending a trigger pulse using the “CTR-0 Out”
to two high-speed cameras synced in time. The trigger is sent to the master camera

as a hardware trigger. The voltages and cameras capture data 

at congruent sample rates (e.g. 1000Hz). We want to be able to link the image
data directly with the voltage data in time, and so in the Labview program
within the "while loop" for obtaining continuous samples of voltage, another DAQ
Assistant is created to send out the trigger pulse (with zero initial delay) at
the same time that the voltage data is written. Ideally, this should mean that,
if the voltage and image sample rates are the same, the data syncs in time. 

My question is this: is there any internal delay (in time) between acquiring
data through the analog inputs (AI-0 and AI-1), and sending out the trigger
pulse through “CTR-0 Out”? If so and this delay is significant enough, it could
mean that the camera images and voltages do not sync in time, which leads to

error.

Please advise! Thank you very much 🙂

[camerond]

---

@JMark111 wrote:

Hello!

I am currently using the PCI-6034E DAQ, interfacing with a BNC-2110 block. We
have two piezoelectric patches fluttering and generating AC voltages, which
are subsequently read by a user-written program in Labview through two analog
inputs in the BNC-2110 block. When activated through the program, the raw
voltages are written to a measurement file.

Along with the voltages, we are sending a trigger pulse using the “CTR-0 Out”
to two high-speed cameras synced in time. The trigger is sent to the master camera

as a hardware trigger. The voltages and cameras capture data 

at congruent sample rates (e.g. 1000Hz). We want to be able to link the image
data directly with the voltage data in time, and so in the Labview program
within the "while loop" for obtaining continuous samples of voltage, another DAQ
Assistant is created to send out the trigger pulse (with zero initial delay) at
the same time that the voltage data is written. Ideally, this should mean that,
if the voltage and image sample rates are the same, the data syncs in time. 

My question is this: is there any internal delay (in time) between acquiring
data through the analog inputs (AI-0 and AI-1), and sending out the trigger
pulse through “CTR-0 Out”? If so and this delay is significant enough, it could
mean that the camera images and voltages do not sync in time, which leads to

error.

Please advise! Thank you very much 🙂

---

IMHO, you're going to have more chances for delays in your software than in your hardware. First thing, I would get rid of the

[Tortu]

Greetings JMark111

Here is some information on synchronization:

http://www.ni.com/white-paper/11369/en/

http://www.ni.com/white-paper/2989/en/

http://www.ni.com/white-paper/4322/en/

Regarding your specific question, the delay between the analog input and counter output should be negligible for your application, since the signal is internally routed. 

Warm Regards,

[JMark111]

Hi Cameron,

Thanks heaps for your reply! I am quite new to Labview so any help with the software wiring diagrams is very much appreciated. You were about to say that I should get rid of...?

Would you like me to upload the current wiring diagram?

Thanks again!

[JMark111]

---

@Tortu wrote:

Greetings JMark111

Here is some information on synchronization:

http://www.ni.com/white-paper/11369/en/

http://www.ni.com/white-paper/2989/en/

http://www.ni.com/white-paper/4322/en/

Regarding your specific question, the delay between the analog input and counter output should be negligible for your application, since the signal is internally routed. 

Warm Regards,

---

Thanks heaps Luis!

Do you have an estimate of the delay (in time units) that could be occurring?

[camerond]

---

@JMark111 wrote:

Hi Cameron,

Thanks heaps for your reply! I am quite new to Labview so any help with the software wiring diagrams is very much appreciated. You were about to say that I should get rid of...?

Would you like me to upload the current wiring diagram?

Thanks again!

---

Don't know what happened to my reply, but I meant to say that you should get rid of the Express VI and wire up one with the attributes you need from the normal palettes. The Express VIs are easy to wire up because you just have to fill in a few blanks, but they are much less efficient than one you wire up yourself because they have to include all the options. Plus, if you want to get better at LabVIEW, you'll have to go "hard-core" sometine anyway, so it's better sooner than later.

My signature lists a couple of the more popular online tutorials, so, IMHO, the best thing you could do for help with the "software wiring diagrams" (aka code) now would be to take some time to work through them.

Cameron

[Tortu]

Greetings JMark111.

I haven't found an article that backs me up on this estimate, however, if you look at the Device-to-Device skew of the PXI signals, you can get an idea of what this time delay will be. Since the delay they talk about in table 2 of this white paper is actually between devices, we can expect internally routed signals to be delayed by even smaller amounts of time (so we probably are looking at the hundreds of pico seconds range). However, your real problem comes from the fact that the exported signal from the PFI has to travel through a cable all the way to the camera. That is where the vast majority of the delay will be. 

Please let us know if you have any other questions.

Warm Regards,