Metal detectors detect metal. All kinds. If you want to discriminate between the useful targets and the junk, learn to use your detector’s discrimination mode.
Discrimination mode helps your metal detector stop responding to certain types of metal objects like steel and common metallic iron. This discrimination is done using various filtering methods and improves your chances of finding more interesting and/or valuable targets.
That’s the basic idea, but here’s a deeper look at metal detector discrimination mode and how to make it work for you.
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How Does Metal Detector Discrimination Work?
Technically, it goes like this: Your detector is “listening” for all types of metal targets. Discrimination is special circuitry that blocks the detector’s audio and visual response to certain metal targets. These targets are detectable along a spectrum sometimes referred to as a metal detector discrimination scale.
You are effectively telling your detector to keep quiet if it senses the undesirable metals. Because your detector transmits an electromagnetic field and gets a response from whatever target(s) it finds, discrimination allows you to filter out the responses that are not useful to you.
Discrimination – Notch Filters
Discrimination features vary in detectors. The most basic type is “variable.” This is implemented by a dial that increases or decreases the amount of discrimination. That’s useful if you understand how much or how little to apply. This comes with experience. However, there is also something called “notched” discrimination where the detector can specify a notch(s) in the continuous conductivity range. This allows metals that fall in that notched-out area to be either included or excluded for alerting. Different manufacturers also have proprietary discrimination settings that can improve the notched discrimination modes.
It should be noted that most Very Low Frequency (VLF) detectors will have a discrimination feature. However, Pulse Induction (PI) metal detectors, which use different technology to find targets, typically don’t.
How to Gauge What Your Detector is Telling You
Starting with no discrimination, your detector is pretty basic and capable of finding all metal within range. As you raise the discrimination level, you’ll start to ignore smaller metallic trash as well as some mineralization in the ground. With more discrimination, you begin to reject things like pull tabs, nails, and foil, but as you go with more discrimination you start to lose some desirable metals like gold, copper, and silver.
It’s a balancing act and something you’ll learn over time. A good way to test the discrimination of your detector against different items is to put samples of various items like coins, foil, pull tabs, and nails spread out on the ground. Starting at the lowest setting, scan the targets separately. For each, slowly raise the discrimination level and note what you see. What materials alert at what level and how does it sound? It won’t take long to learn how your detector responds when it signals various items.
Most modern detectors save you some time in that respect by having a visual indication of the range of items.
Discrimination and Mineralized Soil
Many parts of the country have mineralized soil. This is soil whose particles have some iron content and can be attracted by a magnet. The reason this is an issue for metal detectors is because of the way metal detectors work. The detector coil sends an electromagnetic field into the ground. When it strikes a metal target it sets up small “eddy currents” in the target, which your detector senses and alerts on. These generally aren’t strong enough to set off an alert, but these low-level signals play games with the detector circuitry and mask real targets. With discrimination set at a level to mask out iron targets (generally low-value targets anyway), you have a better chance of knowing about the higher value targets.
Ground Balancing and Mineralized Soil
While we’re on the subject of mineralized soil, it’s worth a mention of “ground balancing.” This is because mineralized soil somewhat masks the presence of targets within the soil. Ground balancing is calibrating the detector’s circuitry to the ground surface. When done correctly, it can cancel the effects of ground mineralization. This allows the detector to sense the targets but not both target and ground. It’s a form of discriminating if you think about it, but not target-type from target-type. Rather, it’s a bit like being able to see through the fog.
There’s a procedure to go through to ground balance your detector, and if done right you’ll neither be positive or negative of the balanced condition. Once you set it correctly, your detector has the best chance of finding what’s down there.
What is the Difference Between Metal Detector Discrimination and Sensitivity?
Discrimination helps your detector keep quiet when it senses certain materials. Sensitivity is just that; how sensitive your detector is to what’s down there. Actually, what’s down there as well as what’s around it. If there are power lines or cellphones or another detector nearby, your unit may alert. It’s too sensitive for that location at that setting, so adjust it until the false alerts stop.
Regarding target sensitivity, at one setting you may detect objects which are non-ferrous or buried deeper. At another setting, you could be able to detect entirely different items. You can see that sensitivity could be used to stop alerts on certain metals, but it’s not nearly as effective as discrimination mode is.
Discrimination Mode and Metal Detecting Beginners
When you’re new to metal detecting, you really don’t have a feel for what your detector does and how it reacts to targets. Any targets. For that reason, it’s smart to keep discrimination mode off for a while. You really need to hear the different alerts and dig on each location to see what it found. As you gain experience, you know what you want to discriminate for. That’s when you can use turn it on.
Different detectors call the no-discrimination by names like “all metal’ or “zero discrimination” mode. Whatever the name, start out that way and you’ll learn how your detector “speaks” to you.
However, if you’re just interested in trying for specific targets from the start, feel free to use one of the pre-set notches. These are helpful to beginners and experienced users alike. Manufacturers do their best to make these features useful and as easy to use as possible.
That said, even with these pre-sets, there is some tweaking you can do to fine-tune things. You just have to understand how it all works so you get the benefit and don’t actually degrade your detector.
Typical Discrimination “Beginner Modes”
Each detector labels these a little differently, but basic categories are:
All Metal – used to detect all metals. Good learning mode to see how different metals sound when they alert
Coin – designed for coins (but may also find foil, nails, iron, and possibly other small items)
Jewelry – tends toward jewelry and coins, and since it’s a wider range of discrimination, can potentially alert on junk than you aren’t searching for
Relic – Alerts on the larger objects with relic potential (relics are things like old coins or civil war artifacts, pretty much defined by age or association with the past)
Prospecting – this setting is for gold, so if you aren’t looking for it or in an area where you’d not expect to find gold, it’s best to not use this mode