Trigger doesn't work sometimes, PCI6132

[jzhj01]

Hi, All,

I am using PCI6132. It was bought only a few weeks ago, and new. My measurement is:

Laser scanning starts (at a start wavelength) -> At wavelength 1, it generate a TTL, start trigger -> DAQ start sampling (finite sampling) -> At wavelength 2, a TTL strop trigger -> Stop sampling, and Show the signal curve -> Laser arrives the stop wavelength, and stops.

The problem is: If the sample rate is set as 10,000 or smaller, the above process can work well. however, if the sampling rate is set as 100,000 or larger, sometimes, it is waiting for the start trigger (seems that the start trigger is not well recognized). So, the laser is set to scan twice continueously. It can give what I want during the second scan most of time.

The TTL signal: 3-4V, rising edge 150us.

so, if sample rate=100,000, the time is 10us between two points....

I don't know what's wrong. Can anyone help me? Thanks a lot!!!!

Possible reason: The terminal box might be not as good as expected, because when it arrive, I fond the PFI0/P1.0 BNC port didn't work for TTL trigger, so I am using the user defined BNC port now.

Best,

jiangjun

[Joel Khan]

I would like for you to try your best and reexplain your situation from the perspective of your code. How many tasks do you have and what type of tasks are there. How do these tasks need to interact. What is your overall goal?

Changing the sampling rate of an analog input task should have no effect on start and stop triggers from a hardware standpoint. It is possible that depending on how you are coding your daqmx code that your VI could interject performance issues.  What are you doing with the triggers?

It will help others who want to help you if you post your code, what version of LV you are using, and what version of the DAQmx driver you are using.

[jzhj01]

Hi, Joel,

I attached the image of the code. It is modified from the example "Acq&Graph Voltage-int clk-Dig Start&Ref.vi".

Before reading data, there is a function to start the scanning of the laser. The laser can generate two TTL signals at two wavelengths, which are used as start and ref trigger.

It works well for low speed sampling, It is very strange that It can not work when the sampling speed is 10 or 100 times higher. Our DAQ card should be able to do that.

thanks.

Best,

Jiangjun

[Joel Khan]

Jangjun,

Where is the start and refrence trigger getting wired to? Is the problem in reading these triggers or in generating them?

<Joel Khan | Applications Engineering | National Instruments | Rice University BSEE> 

[jzhj01]

Hi，joel,

The problem happen when the sampling rate get higher. The laser has been put to another place. I can not do tests now. Thanks for your reply.

Best,

Jiangjun

[Greg_S-Video]

Hello Jangjun

Have you made any progress on this issue?

Please let me know any more details you can provide, I will be happy to assist you.

Greg S.

[jzhj01]

Hi, Greg,

Thanks.

I can not use the Laser with a digital trigger currently. I am using another laser with the analogue trigger. It works fine most of time. Even sometimes it doesn't work, I found it is simply because there are some noise. I attached a figure to show that. The black solid curve it the analogue trigger signal. When the trigger doesn't work, by an oscilloscope, it is found that there is much noise. The signal is not a clean solid curve but thick curve as shown in the figure.

Whenever the trigger doesn't work, I will reconnect the BNC cable from both end. Then it works again.

I don't know what is the reason for this. Maybe it can also explain why the digital trigger doesn't work sometimes.

Best,

Jiangjun

[Patricia B]

Hi Jiangjun,

What does the signal look like when you reconnect the BNC cable? Is it a clean signal?

Regards,

[jzhj01]

HI, Patricia,

I reconnect both ends, then the signal is clean. It is very strange that when I walk around and come back, the signal goes bad again sometimes. I have to reconnect them again.

Best,

Jiangjun

[Patricia B]

Hello,

Would you mind posting pics of both signals?

Thanks,