Multimeter as Lightning Detector


Most digital multimeters
have a sensitivity of 200 mV and in input impedance of 10 MR. With this
information you can calculate that at full scale there will be a
current of 20 nA (nano-ampères). In reality you have a very sensitive
ammeter in your hand. Now that we know this, it becomes a mission to do
something with that knowledge. In other words, here is a solution that
requires a problem…

For example, try the following: Connect the ‘COM’ of the voltmeter
to ground (safety earth from a power point, central heating, plumbing,
etc.). Connect an old bicycle wheel spoke or a length of thin copper
wire to the ‘V’ socket so that you get a kind of antenna. When you place
this impressive looking apparatus on a windowsill during a thunderstorm
and set the meter to the 200 mV range, you will, with a bit of luck,
see nice deflections during lightning strikes. A nice thing is that you
will see a build-up of static charge long before the flash, and
immediately after the lightning flash the charge is gone.

Multimeter as Lightning Detector

Multimeter as Lightning Detector

Be aware of your own safety and those of others: Don’t walk out-side
with the thing or surreptitiously lead the ‘antenna’ to the outside.
This is really dangerous. In these modern times people still die from
lightning strikes! According to theory it is possible to improve the
lightning detector somewhat. A sharp point or edge collects more than a
rounded one. You probably have a razor blade somewhere. Attach this
razor blade at the top of the antenna. And again, be careful: keep
children and pets away. In the picture you can see an assembly were the
top of the antenna has one turn.

The razor blade is clamped in this and in addition it is a lot
harder to injure yourself this way. The ‘reception’ can be improved a
lot more by ionising the air in the region of the antenna with the aid
of radioactivity. Most of the mantles used in gas and petroleum lamps
contain a small amount of radioactive material and also smoke detectors
that work with an ionisation chamber are (lightly) radioactive. It is
better to leave the smoke detectors alone, because they often contain
very poisonous substances, but a piece of lamp mantle could be secured
to the razor blade with some two-component epoxy glue.

Author: Karel Walraven – Copyright: Elektor Electronics Magazine


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