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!