Many investigators have the wrong idea about EMF meters, and the difference between calibrated
meters and un-calibrated meters. So here it is, a detailed description of EXACTLY how AC EMF meters work, and what you should
be looking for in a haunted environment. Hopefully this will clear up any questions you have about meters.
AC EMF meter consists of two basic stages: an amplifier stage, and an output stage. The amplifier stage is where the actual
EMF readings are taken, and the output stage is where is converted to a readable output (i.e., analog or digital meter, an
array of LED's, etc.). The amplifier stage is the one we are concerned with here, it defines how the meter will actually read
AC magnetic fields.
All an AC EMF meter really is, is an inductor (coil)
hooked to an amplifier, similar to an audio amplifier. An oscillating (AC) magnetic field will cause a tiny voltage, say 1-4
milli-volts, flow through an inductor, which is then amplified several thousand times to, say 1-4 volts. The result is an
analog signal, whose frequency is directly proportional to the oscillating field's frequency. That signal is then sent through
several filtering stages, which take the oscillating AC output and turn it into a voltage output, proportional to the strength
of the magnetic field proper. This reading is then sent to the output stage where it is measured, and the appropriate reading
in Gauss (or Oersted) is displayed. So, the effect is the exact opposite of an electromagnet, instead of AC current through
a coil creating an AC electromagnetic field, AC electromagnetic fields create an AC current in a coil, which then can be measured.
Calibrated vs. Un-calibrated
Calibrated - Many people think
that because a meter is calibrated at 50/60hz means it will not pick up other frequencies. This is entirely untrue! A "calibrated"
meter uses what we call a differentiator amplifier, which sends the input current through capacitor before entering the amplifier.
This will make the meter read higher frequencies as a higher reading than lower frequencies. When a meter is said to be calibrated
at 60hz, it means that it will give an accurate Gauss reading at 60hz, but as the frequency of the field goes up, the amplification
goes up proportionately! For example, if we had a 1mG field oscillating at 60hz, the meter would read 1mG, but if we had a
1mG field oscillating at 120hz, a higher frequency, the EMF meter may actually read 2mG, instead of it's true reading of 1mG.
I've made the following graph to help you better understand how calibrated meters read other frequencies:
- An un-calibrated meter has just a straight amplifier, with no capacitors at all (except maybe one
across the feedback resister to roll amplification of high frequency fields (>10khz), this is only to block radio signals,
though). The only distortion in the field reading is caused by the inductor's own self resonance, which doesn't effect the
meter until extremely high frequencies (>1khz) are reached. The problem with calibrated meters, though, is it is very hard
to get an accurate reading, because of electronic errors such as natural DC biasing from voltage drift. The same capacitor
that makes the calibrated meters amplify higher frequencies more, blocks these DC fields from the amplifier input, and will
only allow oscillating AC fields to pass into the amplifier stage. A truly un-calibrated meter should give an accurate reading,
no matter what the frequency (under 1khz).
So which is Better??
I don't know! An un-calibrated
meter will give a true reading no matter what the frequency, but is it because calibrated meters amplify higher frequencies
more than lower frequencies the fact they are going off? For example, I built an un-calibrated EMF array that is more sensitive
than the original calibrated EMF arrays we use at the research site. At 60hz, my meter is more sensitive, but as the frequency
goes up, my meter still reads the same (as it should), but the calibrated array goes crazy. In fact, if the frequency is high
enough, the un-calibrated meter will be at full-scale deflection (>10mG) before the un-calibrated meter even reads 1mG.
In other words, if spirit magnetic field shifts are at a higher frequency, a calibrated meter would be better, but if they
were a lower frequency, an un-calibrated meter would be better.
Ok, so I bought a meter, but how do I know when a
spirit sets this thing off??
Ok, first of all you need to learn that AC magnetic fields do not
define paranormal activity. Yes, in our research we have found that in known haunted environments, AC and static magnetic
fields sometimes have anomalous changes, this is true. But there are also uncountable devices that put out low frequency AC
EMF's, particularly in the 50-60hz frequency range, but that's not what you should look for in a haunted environment. What
we are looking for are anomalous changes in the baseline field, at different frequencies. In many cases we have found that
the anomalous magnetic field shifts are extremely low frequency (lim(x->0)-2hz), and are associated with the static magnetic
field of the Earth itself. The AC EMF meter you are using probably isn't built to measure such a low frequency field, but
if the derivative (acceleration), or velocity, of the moving field is fast enough, the field can create the appearance of
being an AC field from the inductor's point of view, because a small current is produced in the inductor by a quickly moving
static field, which gives the meter the illusion of an AC field. So, if you are holding the meter in one position, the reading
should not change very much, this is called the "baseline" field. Any large changes (positive or negative) in that reading
can be considered anomalous, and potentially from spirit activity. Be careful, though, because moving the meter around or
changing directions quickly can cause a small current in the inductor, which will give a brief false-positive reading. If
you are using a hand held meter, the best way to sweep the area is to walk slowly with it, keeping the meter movements as
smooth and slow as possible. If your baseline is about .4 mG, and when the meter is still the reading suddenly jumps up to
.9 mG, and back down to .4 mG within a matter of seconds, or milliseconds, this can be considered anomalous, and potentially
caused by spirit activity.
What the heck is difference between Single-Axis and Tri-Axis meters?
AC magnetic field is oriented the same way a regular bar magnet is, only the N-S fields are constantly interchanging at a
given frequency. In other words, it has a north pole, a south pole, and a neutral pole between the two. A current will only
be inducted in an inductor if the poles are parallel to the coil. A single-axis meter has only one inductor, so it could be
right on top of a strong AC magnetic field, but if it's facing the wrong direction, it may not even register. A tri-axis meter
has 3 inductors, one on the X axis, one on the Y axis (perpendicular to the X axis), and one on the Z axis (perpendicular
to the X and Y axis), so no matter what the orientation of the field or meter is, it will still give an accurate reading.
Most of the meters we use are single-axis (like the GaussMaster and 200A), and a few of the more expensive meters are tri-axis
(like the TriField meter).