Photon counting using R series FPGA. Problem generating TTL signals

[iron_curtain]

Greetings,

I'm trying to use NI R series FPGA to read and count the TTL pulses from a discriminator (Hamamatsu C9744 photon counting unit) connected to a PMT (Hamamatsu H7422P-40). The output from PMT looks fine (H7422P-40 signal.png) but the discriminator was not able to generate corresponding 5V TTL pulses. There were some sparse and random spikes but nothing meaningful. Instead, the only stable signal from the PMT was a single +5V pulse no matter how I adjusted the control voltage of the PMT (C9744 output.png). The PMT and the discriminator is connected by a regular 50 ohm BNC cable.

I'm really puzzled because it was supposed to be a really simple setup. Did anyone have similar issue or have the similar instrumentation setup (but without issue)? Any comments/suggestions are greatly appreciated.

Thanks very much in advance!

[ikelli]

Have you ever had this connection working and it now is giving you problems, or is this an initial setup.  Have you verified that you have all of the correct drivers loaded onto the FPGA that are necessary for your hardware and application?

[iron_curtain]

Hi Kelli,

This is an initial setup for photon counting. Previously our imaging system was operating in analog mode which fed amplified PMT signal directly to analog input port of NI R series FPGA. It worked fine but we'd like to try photon counting mode to improve the SNR.

All drivers were loaded correctly. 

Thanks.

[ikelli]

I need more clarification about your setup to understand your problem because I do not know the Hamamatsu equipment.  You say that the Hamamatsu H7422P-40 works fine.  Do you know what your expected output of the Hamamatsu C9744 is and the expected frequency? From a quick look at the website description, I am understanding that the output should be 5 V.  Have you tested using anything other than the R Series FPGA to verify that the output is correct in other environments? For example, if the device works using an oscilloscope but not using the R Series card, we will have some trouble shooting steps to take.  In that case, what is the card you are using?

[iron_curtain · Accepted solution]

Hi Kelli,

Thanks for your help. Sorry it took so long to get back to you.

I actually figured out the issue. The discrimination level of  the Hamamatsu unit was set too high that all signals got filtered out. After manuallyt adjusting the threshold I was able to get TTL pulses from the unit. And 7842R worked properly to count the pulses. Everything works fine now. Thanks again for the input. 

[hoanlv]

Hi iron_curtain,

I am a student in Korea, I also have a NI FPGA board 7842R and photon counting program as you have. However, It runs very slow, I am a beginer in labview and FPGA, so I would like to ask you a favor, could you let me see your vi. or teach me to do photon counting ? 

My email: lehoan.bme.bk@gmail.com

[iron_curtain]

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@hoanlv wrote:

Hi iron_curtain,

I am a student in Korea, I also have a NI FPGA board 7842R and photon counting program as you have. However, It runs very slow, I am a beginer in labview and FPGA, so I would like to ask you a favor, could you let me see your vi. or teach me to do photon counting ? 

My email: lehoan.bme.bk@gmail.com

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Hi hoanlv,

The slow speed might be due to either hardware (slow photon counting unit) or software (LabVIEW FPGA code). Can you please start a new post with more details on your setup so I (and other members) can give you more specific suggestions?  Thanks.