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EMI interference

What is EMI Interference? The definition is quite broad and a bit confusing for non-technical people:

Electromagnetic Interference (EMI) is any signal or radiated into space or transmitted through power or signal lines that threaten the operation of radio navigation or other safety services, or seriously degrades, blocks, or repeatedly interrupts licensed radio communications. Radio communication services include, but are not limited to, television and radio broadcasting, mobile telephony services, radar scanning, air traffic control, paging services (pagers), and PCS (Personal Communication Services). Licensed radio services, such as those used in WLAN networks or Bluetooth technology, together with incidental transmitters, such as digital devices including computer systems, contribute to the electromagnetic environment.

In our case, these are simply interferences that make the work of the metal detector difficult or even impossible. Half the trouble is when the process is visible and the device characteristically excites, generating a target signal and a numerical ID. Then we know that we are dealing with them and can take appropriate measures. What? Detuning the so-called changing the channel, reducing the sensitivity, or choosing a different operating frequency, if possible, direct elimination of interference sources such as telephones, transmitters, electric fences for animals, etc.

In difficult cases, you can use discrimination and cut-out interference, but this is only a half-measure. We lose performance, which is already heavily limited by EMI interference. A colleague who accompanies us can effectively deprive us of the chance to find finds, being even several meters away with his detector! Don’t fall for the group search, it’s just a nice time at the rally, you can’t count on the effects in such conditions. It’s unlikely!

What was the better situation, and what is the worse? Quiet disturbances. The ones that are not visible, and everything seems to be ok. We lose performance, but the detector does not signal it in any way. You can put a coin under the probe and the device can be completely blind. How to defend against it? It depends on many different factors, and above all on the type of device we have.

We preventively check other programs and detune the device from time to time. We check the signals with the person next to us to see if our detector can handle them as well. It’s the only option. SMF-type machines – simply put, multi-frequency machines, usually work in two or more frequencies, processed by software. In some cases, it may turn out that what was supposed to be a great advantage of a wide frequency range becomes a disadvantage!

For example, we have a program working in the range from 5 to 40 kHz – ideal for searching for gold, i.e. a low conductor is allergic to high frequency, and silver – a high conductor to low frequency. In addition, high frequency copes with small things better and with greater mineralization of the ground. In the case of low frequency, objects with a larger volume are signaled better. Story. We will not miss anything from what interests us the most!

Unfortunately, right now our greatest enemy is approaching and eliminating one of our frequencies. Without seeing it, we lose 50% of the possibilities without knowing it. Often programming and filters sewn in with it additionally stabilize the work of the detector. For this reason, the prevention described above is important. In this way, we will avoid erroneous opinions about the equipment and unreliable tests, especially from the test tracks. Interference can confuse us, so it is worth spending many hours checking different variants of settings in the field in various conditions!

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