Lesson Learnt: EMI

For the whole month of July I had been concerned with my measurements being too high, about 3 times what everybody else seems to measure.

I never had 100% confidence that my instruments was telling me the truth, probably because I assembled it myself from a kit. On top of that, every time I switched on or off an electric fan or a neon light in my apartment, I was getting a spike in the measured values. I learnt to live with that, and my data post processing procedure takes care of that and removes those spurious spikes. A few weeks back I also added ferrite chokes to the cables plugged into the unit, and the spikes induced have become a little smaller.

Yesterday finally I decided to wrap all the cables and the instrument itself in aluminum foil, and voilà, today the reading was down by a big step. Now my reading are only about twice what other stations report. Big improvement !

I have a feeling that I am getting close to doing accurate measurements, even though I think there is still some residual EMI to be shielded off. In the next few days I will replace some internal wiring with coaxial cables too.

Now that I am getting closer to a more realistic ball park range of measured data, I am also starting to think that the formula that I am using from converting from CPM to μSv/h is correct (the tube is an LND 712)

123 CPM = 1 μSv / h

but I would still appreciate if anybody could add any comment.

In light of this, I will also have to update and replace the picture in the “Histogram” page, but I’ll get around that in a few more days.

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