Help with Single photon counter (SPCM AQR 15) for fluorescence detection and trigger a solenoid valve by labview

[MatthewTang]

Do you mean the spikes I got from DAQ are normal?? Why the signal is so different from the one I got from oscilloscope?

One mre question: what would happend if more then one photons arrive the photon counter at the same time? Would it count as one or two, or voltage increases in this case?

Best,

Matt

[MatthewTang]

I just have a sense that I am getting random signals from the DAQ, but not the real signal I expect. I connect my BNC output of photon counter to BNC 2120 which then connects to USB 6251. 

I tried switching the "FS" and "GS" on the analog BNC on BNC 2120. What I could get is sometimes a small ampitude sine wave or square wave (same frequecy, around 40-50Hz). I used RSE mode 

[John_P1]

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@MatthewTang wrote:

Do you mean the spikes I got from DAQ are normal?? Why the signal is so different from the one I got from oscilloscope?

One mre question: what would happend if more then one photons arrive the photon counter at the same time? Would it count as one or two, or voltage increases in this case?

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According to the datasheet the photon detector should emit 30 ns pulses in response to incident photons.  You shouldn't be able to see these on the DAQ card's analog input as the -3dB cutoff is specced at 1.7 MHz.  You need to be using the counters.  The input signal would be wired to a PFI line.

I can't speak for the manufacturer of your photon counter... but in principle if more than one photon arrives at the exact same time it would only be registered as one.  Statistically this is rare enough that it is not a factor until you reach the "saturation point" (described in the data sheet) at which the light intensity is high enough that this becomes an issue.  

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@MatthewTang wrote:

I just have a sense that I am getting random signals from the DAQ, but not the real signal I expect. I connect my BNC output of photon counter to BNC 2120 which then connects to USB 6251. 

I tried switching the "FS" and "GS" on the analog BNC on BNC 2120. What I could get is sometimes a small ampitude sine wave or square wave (same frequecy, around 40-50Hz). I used RSE mode 

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Sounds like noise.  The analog input doesn't have the bandwidth to see a 30 ns pulse which is what should be emitted from the photon detector if it is working properly.

Best Regards,

[MatthewTang]

So I couldnt use my photon counter to tirgger my solenoid valve? Is it possible to set a threshold and once it detect a peak from the photon counter it holds the signal for some secs?

Also, i found that my DAQ assistant in labview shows error if I used 1.25M sample rate.... Is it because of the insufficient ram of my computer? I have 4 GB ram in my PC.

😐

Best,

Matt

[John_P1]

You could use the 30 ns signal to trigger a counter output of a configurable duration of time if you wish.

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Also, i found that my DAQ assistant in labview shows error if I used 1.25M sample rate.... Is it because of the insufficient ram of my computer? I have 4 GB ram in my PC.

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Are you still talking about the analog input task?  This isn't the route you should be taking.  The counter task doesn't need to be sampled so quickly, the counter will increment when it sees a pulse regardless of how quickly you are sampling.

Best Regards,

[MatthewTang]

I think I don't want to count the number of photons... I just wanna use the signal to trigger my valve.... would this still be possible?

[John_P1]

Yes, try this example:

https://forums.ni.com/t5/NI-DAQmx-Examples/Generate-Retriggerable-Finite-Digital-Pulse-Train-from-Co...

Connect your signal to a PFI line and configure this as your trigger source in the example.

Best Regards,

[MatthewTang]

Seems there is still hope... By the way what is PFI???

[John_P1]

PFI  (Programmable Function Interface) lines are terminals on the DAQ card that can be used to route timing and triggering signals.  Check your device pinout.

Best Regards,

[MatthewTang]

Do you mean the blue cable connecting my BNC2120 to USB 6251? I am a bit confused....