Dear colleagues,
we use Canberra Digital MCA to connect a Canberra BEGe detector, and at the same time we use a Tektronix Oscilloscope to check the output signal of BEGE preamplifier. We found that there is a periodicity signal, ~3 us, would appear in the output signal(see the picture). The technical of Canberra said that was caused by High Volt power supply. But we change the HV supply, it also appeared.
so is this normal when deal with the HPGe signal? if not, are there another some facts should be considered?
thanks!
Hi,
If this doesn't come from your power supply, it then comes from the electric network. You should check if the grounding of all your electronic chain is properly done. Is the power output on a protected network or is it on the main grid. If it is on the maingrid, I would recommend having an isolation transformator.
If it doesn't come from the power source, then check all the equipment for noise with your oscillloscope.
This in any case does not come from the germanium.
Good luck and welcome to the wonderful world of Electromagnetic compatibility.
3 usec: you mean the period that occur the noise signal?
did you apply HV?
To add to Julien, when you got an isolation transformator (IT) make sure everything is isolated (wastebags as long as they aren't antistatic do a good job!). Also the scope needs to be on the same ground. Often a good grounding helps to improve the resolution (~1/2 keV at 1332.5 keV). Hope it helps.
Hi,
Usually, such spikes go from switching circuits. See fig.41 http://www.ti.com/lit/an/snva559/snva559.pdf
There are a lot of power devices with switching circuits inside. ~(3 us)^-1 is RF frequency, so this can be EMI from any loads powered by switching power supply. Try switch-off any possible sources.
You can search EMI sources by simple handmade inductive sensor connected to scope.
Have you checked the preamp supply ?
How is the detector cooled ? Adding LN2 by hand (no problem), connected to an autofill ? (remove bayonet / check autofill) Sterling pump ?
regards
Dear all, thanks for the answers and the shared experience. Now we can confirm that this problem is caused by the low-volt supplier, both Canberra and Ortec. These two LV supplier is highly integrated and very compact! When we used an single NIM LV supplier, the noise signal disappeared!
The finding road is not easy until we found a EMI test platform.
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