Weird signal reading of photomultiplier tube

Wierd signal reading

Hi,

Need some help to point a direction for which I can search for some solution to my problem

I have recently acquired a new digitiser card which is supposed to digitize the analog signal from my photomultiplier tube setup(a pmt detector connected to an amplifier). It seem to give me some quite strange square pulse signal(shown in the figure photodetector 1 and 2) when I am supposed to get some sinusoidal like looking waveform


PhotoDetector1


PhotoDetector2

The square pulse seem to have a period of 50Hz. I am wondering if this is some power ripple noise or digitising problem

I have tried to connect this digitiser to a function generator. A proper sinusoidal signal is observed shown in Function generator.jpg


Function generator

Need ya guys help to point out a direction that I could start to troubleshoot

Thanks a lot

Re: Wierd signal reading

Hi!
I think is a problem with some interference.
You should try to use shielded cables.See also if the connection to ground is made proper.

Best regards!
Venix

Re: Wierd signal reading

Have tried to use a shielded cable to connect to the digitizer but does not seem to solve for the problem.

It is pretty strange as I do not have any such signals when I am working with my old digitizer

Wierd signal reading

What is the make and model of the digitizer?

/Ram

Re: Wierd signal reading

Hi,

I think I have kinda solved for the problem... added a few resistor as the source impedance seems quite high...

THanks