How To Ground-Balance a Metal Detector Properly

1. What is Ground-Balancing and Why it is Crucial for the Process

Ground Balancing is a calibration of the metal detector's circuitry to ground conditions. If done properly, it reduces or completely eliminates both the Ground Falsing (annoying audio responses caused by minerals in the ground matrix - ) and the interference that ground mineralization has on VDI values of detected targets - all detailed info is given in my article - Factors That Affect VDI Readings of Non-Ferrous Targets

Any soil contains non-conductive iron minerals, and some soils contain dissolved conductive salts. The level of mineralization in the ground depends on the area's geography and location as well as former and current presence of any human activity (industry, agriculture, etc.), or both. In areas with high levels of mineral content, mineralization masks metal targets, virtually making them "invisible" to any VLF metal detector operated in the All-Metal and Motion Discrimination modes IF the Ground Balance is wrongly adjusted.

Types of Ground Balancing

FACTORY PRESET G.B.

AUTO-TRACKING

AUTOMATIC G.B.

Depending on the VLF metal detector's class, the ground-balancing procedure can be performed either manually by a detectorist or automatically by the detector's Automatic GB circuit (also called Automatic Ground Compensation and Ground Tracking). This circuit monitors changes in the ground mineral concentrations and re-balances itself without operator involvement. Some advanced metal detectors, including machines that are designed for gold nugget or relic hunting, have both options available to their users. Cheap metal detectors usually do not have any GB controls, and the ground balance is factory preset - which is not good for serious metal detecting. Pulse Induction (PI) metal detectors do not have the GB circuit or mode because their performance is not affected by mineralization.

Automatic GB can be beneficial for those who do not like to bother with the GB controls every time the ground mineralization intensity changes, and let the detector's microprocessor do the work. Usually such hobby enthusiasts pursuit GENERAL metal detecting (searching for coins, buttons, jewelry and whatever else may come along) in areas with low mineralization. But to relic hunters who search in the All-Metal mode of operation on highly mineralized grounds, or gold nugget and meteorite hunters who often deal with extreme ground conditions, using the Automatic GB is out of question because, in each case of heavy mineralization, the Automatic GB may greatly reduce the detector's Operating Depth Range. Even the most advanced metal detectors with the automatic ground-tracking circuits cannot overcome this problem. Generally all "automatic ground-trackers" cannot compensate for various mineral concentrations in the ground when encountering a series or a cluster of them at one spot.

Many hobby enthusiasts claim that the automatic ground-tracking technology has recently advanced so much that the Automatic GB gets the same results as the manual ground balancing. I would certainly disagree with this statement, and my line of reasoning would be based on my own practical experiences and tests conducted under real metal detecting conditions in the field. I strongly believe that the Automatic GB is designed only to make the search process easy and comfortable for inexperienced and "slacking" detectorists (hey, I've been there, done that too! :))). If you want to have good results in metal detecting, you have to use the Manual GB. If you would like to understand the mechanics of the manual GB adjustment, and your metal detector is operated in the Non-Silent mode (also called 'Threshold Mode') incorporating the Manual GB, read on!

MANUAL G.B.

Of course, among those who pursuit general metal detecting on the low-mineralized grounds, there is a minority of detectorists who use the manual ground balancing. They do so to their advantage and, thus, get the highest results. Ultimately, such detectorists like being in total command of the ground balance which, if adjusted right, can optimize Ground Penetration, Target Identification and Pinpointing, and make the search operation quieter. The only inconvenience of using the manual GB is that you have to frequently re-balance your machine during the search. Usually an increase of the ground 'noise' (in the Motion Discriminate mode) or decrease in the threshold level (in the All-Metal mode), or even its disappearance, is a good indication of the right time for re-balancing.

The objective of the manual ground balancing is to achieve no change in the All-Metal mode's Audio Threshold (constant background humming) when performing the procedure called "pumping the coil" - slow raising the search coil up to 12 inches (30 cm) above the ground and then lowering the coil to 1 inch (2-3 cm) off the ground surface. When the Audio Threshold is stabilized, the metal detector will be ignoring ground minerals under the search coil. It really does not require a lot of practice to converge on the "null zone" (also called "null setting" and "zero setting") - a narrow segment (a fraction of the knob's turn, or a few points of the touch-pad control) located someplace within the GB control's range. With the GB control being positioned at the null setting, the ground noise will not be heard no matter which way you move the coil.

If you cannot find the null setting during the ground balancing procedure, or the null zone is too wide, and you hear loud, inconsistent ground noise, you may have been trying to ground balance over a spot where there is a deep metal target, hot rock or the widespread mineral source of high intensity. Just resume searching for the 'clear' spot until you locate one. If you are in the extremely mineralized area and fail to find the null setting while trying to manually ground balance your detector at any relatively "clear" spot, reduce the Sensitivity level as low as needed to locate the best 'clean' spot. Frequently check the GB setting to see if the ground conditions have changed enough to make a new adjustment accordingly and maintain optimal performance of your metal detector.

What is AUTOTUNE?

Some modern advanced detectors with the manual GB option also incorporate the Automatic Retuning (Autotune) feature. The Autotune circuitry is designed to restore the Threshold Audio level when the circuit drift occurs due to mineral interference or changes in ambient temperature when the detector is operated in the All-Metal, Pinpoint or Manual GB modes. This feature allows a user to detect without worrying about changes in the Threshold Audio level. Also, during the ground balancing procedure, the Autotune automatically re-tunes the Audio Threshold. Some detectors have a variable Autotune control allowing the user to adjust a rate of the automatic retuning by following a simple principle: the heavier the mineralization, the faster the Autotune should be re-tuned.

The Autotune feature was first incorporated in metal detectors back in the 1990s when valuable targets were in abundance at most hunt sites. Just like the Automatic GB, the Autotune was appreciated by those detectorists who did not want to bother with optimization of the detector's performance. Today the good targets are so scarce that they can be detected only if all the detector's key features are implemented; the Manual GB being the most important one. And the Autotune is not used by experienced detectorists because it does not allow the user hear changes in the Threshold Audio level, which indicate changes in the ground mineralization and alarm the user that the detector must be re-balanced.