There are two main types of EMF detection:
Passive detection
And active detection
Passive detection is cheap and easy but does not give accurate results. Active detection is a bit more complicated but yields better results. Passive sensing in general does not require much power, if any, to detect. Active, on the other hand, generally requires power to the sensor and—in many cases—looks for a change in either current flowing or voltage changes.
Active sensing is a much more accurate method of EMF (electromagnetic field) detection.
Passive EMF detection is used in the K-II (K2) meter, EDI and EDI + (to name a few).
Active EMF detection is used in the TriField meter, MEL meters and the “Ghost Detector” meter.
Passive EMF detection utilizes a co-planar loop printed on the circuit board or coiled wire for the sensor. I have a detailed write up on the K-II (K2) meter and how the co-planar loop works in another blog post. Active EMF detection instead uses an inductor for the sensor.
What does a ghost hunter need to know about how EMF meters work?
An inductor, when charged, stores energy in the form of a magnetic field. Think about water flowing through a pipe (current). The pump pushing the water is our battery and the pipes are our wires. In our water pipe circuit, we have a water wheel. This is very heavy and once it gets moving is hard to change speed (it has inertia). This wheel is our inductor. Once the wheel is spinning, it does not provide any resistance to the water flow. If we turn off the pump, the wheel will continue to spin (momentum), pumping water as it slows down.
Like the water wheel, inductors don’t like change in flow (current). When current increases, the inductor tries to stop it with an opposing force. When the current decreases, the inductor tries to stop it by pushing electrons to keep the electrical current the same.
These changes can be measured. You can apply an external magnetic field to the inductors’ own magnetic field. This will change the total magnetic field and the inductor will respond to these changes either by opposing the change or by pushing electrons (depending if the change is a decrease or increase).
We can measure the change in flow (current) in the circuit and compare to known values to get a reading of EMF being detected by the inductor.
Active and passive EMF detection are the most common types of EMF detection. Active detection is more accurate than passive detection but comes with a more complex circuit.