Photon counting using PCI 6115 counter. Problems with oscillations

[MagnusBL]

Hi everyone.

We are using a PCI 6115 card with a 2110 BNC connector block to try to read the TTL output pulses from a discriminator (ARI FT100) connected to a PMT (Hamamtsu R4700U). When we turn on the high voltage source for the PMT we get high frequency oscillations on the connection between the discriminator and the 2110 BNC connector block. The counter reads these oscillations as a signal making it impossible to read the number of actual photon pulses being generated. When we switch of the high voltage to the PMT, the oscillations remain, but disappear when we disconnect the cable from the BNC connector block. 

I suspect there is some mismatch between the output of the discriminator and the input to the 2110 BNC/PCI 6115 which causes these oscillations. I tried to attach a 50 Ohm BNC terminator on the connector block with a T-shaped BNC plug but to no avail (only a slight change in the amplitude of the oscillations).

Any ideas on how to solve the problem is greatly appreciated.

Kind regards

Magnus  

[ninlmartijn]

Dear Magnus,

thank you so much for your post on our webforum. Are you seeing glitches on your signal and are thos causing your counter to count pulses which are not really there?

Best regards,

[MagnusBL]

Yes, that is correct.

[John_P1]

Do you have a an oscilloscope capable of measuring the output of the discriminator?  I'd be interested to see what the signal actually looks like.  Depending on the characteristics of the signal, you may be able to filter out the unwanted oscillations.

Best Regards,

[Jiefeng]

I met the similar problem when trying to use H7422P-40 PMT and C9744 photon counting unit from HAMAMATSU. Anyone has any idea?

[alexS88]

Has anyone solved this problem, as i am having similar issues with the C9744 photon counting unit from HAMAMATSU

[MagnusBL]

I was transfered to a different project so I am not actively working on this systems now. From what I remember we were not able to solve this while I was working with the project. I would be very interested to here if you find a solution to the issue.

[me22]

I was having similar problems with my Hamamatsu PMT setup as well. Initially I was receiving a background noise at a frequency of around 2 MHz.  I was able to filter out the unwanted oscillations by using an INLINE 50 Ohm terminator (2 W). With this setup I can now read my signal very well.

[Henrik_Volkers]

A cause of oscillating output buffers is a too high capacitive load (50 Ohm cable is about 100pF/m).   A typical workaround is a series resistor at the output of the driver or a resistive load ... all to get a more real load.