Zero Voltage Transmission (ZVT)
Detector Technology Knowledge
Fundamentals of GPZ 7000 Technology: Zero Voltage Transmission (ZVT)
Basic Principles of Togam Detection
All metal detectors emit a fluctuating magnetic field from their coils (1). When this field interacts with a metal target, it induces an electric current within the target known as an eddy current (2).
These eddy currents then produce their own magnetic field which is different from the magnetic field sent by the detector coil (3). The transmitted field is also
This causes the ground to generate a magnetic field that differs from the one transmitted by the metal detector and from the target’s eddy currents (4).
The detector’s coils sense the magnetic field from the target’s eddy currents, as well as the magnetic field generated by the ground. These coils measure how quickly the magnetic field changes, not how strong the field is. For example, the coils will not respond to a static, unchanging magnetic field, even if it is strong. The coil also detects changes in the surrounding magnetic field, such as electromagnetic interference from nearby electrical sources and lightning thousands of kilometers away (4).
The ground signal has a predictable type of response caused by the transmitted magnetic field, and thus can be recognized by the processing electronics and canceled; this is called ground balancing. Any magnetic signal received in response to a transmitted field that differs from the one transmitted directly and also differ from the ground assumed to be caused by the target metal and reported to the operator.
Ground Balance
A metal detector’s ability to perform effective ground balancing varies greatly between technologies and models. Many detectors only provide approximate ground balancing rather than true ground balancing.
The signals generated in the ground by transmitted magnetic fields generally consist of three different types:
Reactive Soil Components - Is the largest; the signal that is identical in shape to the transmitted signal. This is called the Reactive Ground Component, often referred to as the X component.
Viscous Remanent Magnetism Component - Signals from microscopic magnetic particles, approximately 30 millionths of a millimeter in size, produce complex signals that can be described as & ' delayed response' of the transmitted field, depends on all previously transmitted fields, but more related to the newly transmitted field. This is called Viscous Remanent Magnetism (VRM).
Copy Component - Eddy currents in wet soil often cause a significant portion of the ground signal to be unbalanced in high-frequency VLF gold detectors.
Comparison of Soil Balancing Technologies
Comparison of Ground Balancing Technologies The biggest problem is trying to eliminate the signal from the ground, which can be very large compared to the weak signal from a deep metal target.
Very Low Frequency (VLF) - VLF sinewave detectors have the major drawback of having to balance all ground signals simultaneously (all three ground components above).
Pulse Induction (PI) - PI metal detectors have the major advantage of not detecting the main ground signal; the X component, only the copy component, which is mostly insignificant, and the VRM component, which is only a small percentage of the X component. This makes the ability of PI technology to balance the ground much more accurate compared to VLF detectors. The disadvantage of PI is the lower ability to detect very small nuggets compared to VLF detectors.
Another disadvantage of PI is its ability to detect very large nuggets compared to CW metal detectors, such as ZVT. CW stands for Continuous Wave and includes all technologies that do not have a zero transmission period (almost all technologies other than PI).
Zero Voltage Transmission (ZVT) - ZVT has the same main advantage as PI for soil balancing as it does not detect the main soil component X, but has the same advantage as CW metal detector technology compared to PI for detecting very large nuggets as ZVT is CW (as opposed to PI which is
not CW), and also has the same advantage as PI in that it is relatively insensitive to satin ground compared to VLF.
What is a ZVT transmission field, and how is it different from PI?
Figure 1. The field transmitted by the ZVT varies over time.
Both the ZVT and the PI measure the signal (receiver signal) immediately after a very rapid change in the magnetic field. During the receiving (measurement) period, the PI transmits no magnetic field at all, while the ZVT transmits a very constant magnetic field (until the next very rapid magnetic field change occurs). The ZVT's transmitted field alternates between transmitting very steadily in one direction; for example, the North Pole pointing into the ground; then quickly switching to the South Pole pointing steadily into the ground, then back to the North, and so on.
Why the term ZVT?
More complete definition ' '
because it is directly proportional to the reactive voltage of the transmission coil. The field transmitted by the ZVT is designed to be as constant (unchanging) as possible during the reception period; this means that the reactive voltage of the transmission coil must be zero during this period of constant field, and so must the reception signal derived directly from the transmission coil’s field. Therefore, Zero Reactive Voltage (ZVT) Transmission refers to this ultra-stable magnetic field period during which reception occurs.
Similarly, the signal from the ground reactive component, X (primarily the ground “ferrite”), also produces a zero reception signal if the reactive voltage of the transmission coil is zero; exactly the same as during the reception period of a PI detector. ' '
Figure 2. The received signal from the sensor coil after a very rapid change in the magnetic field, measured during a constant current period. The Time Constant or TC of a metal target is essentially how quickly the eddy current fades.
Figure 2 shows a comparison between a ZVT VRM ground signal and an equivalent PI VRM ground signal; both transmit bi-polar magnetic signals, with the same fundamental frequency and rapid magnetic field change period. It should be noted that the PI receive period is half that of the ZVT, because the PI system in figure 2 transmits for half the time and receives for the other half, as opposed to the ZVT which transmits and receives most of the time.
A key difference in the VRM signal is that the PI signal fades more quickly than the ZVT system. This indicates that the PI receive signal is less sensitive to longer Time Constant (TC) components compared to shorter TC targets than the ZVT, and this is one of the main reasons why the ZVT technology is better at detecting large nuggets compared to the PI; another key reason is the twice as long reception period in the ZVT compared to the PI for the same fundamental frequency. A significant technical achievement of the GPZ 7000 ZVT technology is in creating an ultra-stable transmitted magnetic field during the reception period, to ensure that the large reactive component of the ground signal, X, is not detected, just as in the PI.
GPZ 7000 Super-D Coil
The GPZ 7000 hook must be symmetrical about the left-right axis because the transmitted ZVT signal causes a certain type of signal from the ground that is not present during the reception period. PI. The ZVT reception signal originates from the magnetic hysteresis of the soil. If an asymmetrical coil such as Double-D is used, the coil will produce a signal that depends on the speed of the movement.
coil above ground, and the audio pitch will be higher when moving in one direction and lower in the other, which is unacceptable.
To avoid these issues, the GPZ 7000 uses a coil consisting of two D-symmetric receiver coils, one on the left and one on the right of the central oval transmission coil.
The Super-Early coil geometry means that for targets near the coil surface, the target produces a dual audio response as the coil sweeps the target, with a separate equal response for each receiving coil.
For targets farther from the coil’s surface, the coil behaves more like a traditional coil. The GPZ 7000 is specifically designed to minimize responses to friction and impact, which can cause false signals.
GPZ 7000 Performance Excellence
Measuring detector performance depends on many factors, including specific detector settings, coil size and configuration, soil type, mineralization level and type, electromagnetic interference, gold nugget size and composition, and, of course, operator skill. Figure 3 shows the percentage increase in depth for the GPZ 7000 compared to the GPX 5000, using the same sized coil (14 inches). This data was obtained at several locations and under different soil conditions in Australia.
For this measurement,
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The GPX 5000 uses Monoloop with Fine/Enhance settings in highly mineralized soils, and
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The GPX 5000 uses Double-D with Normal or Sharp, compared to the GPZ 7000 Difficult+ General in moderately mineralized soils.
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GPZ 7000 General compared to GPX 5000 Sharp or Normal (also referred to as ' GPX 5000 Normal' ) using monoloop in moderately mineralized soil.
Nugget weight menu runs from left to right
Here, the vertical Y-axis represents the gain as a percentage, and the horizontal X-axis—from left to right—represents the decreasing mass of the nuggets, starting with number 1 for the 20-ans nugget and ending with number 30 for the 0.13-gram nugget. The X-axis is not depicted on a specific scale; it simply lists the nuggets available for testing in descending order of weight. Profit in nugget depth with
Values above 30 (30–35 fall between 0.13 and 0.05 g) are off the scale; they exceed 60% and are therefore not shown on this graph.
The reason the data is so scattered is that the two different technologies respond differently to changes in eddy current; they differ in their Time Constant (TC). The Time Constant varies significantly from nugget to nugget even when they have the same mass; that is, while the X-axis values for the nuggets decrease based on the nugget’s weight, this does not always correspond to a continuous decrease in the Time Constant. As can be seen, the gain in depth varies significantly from nugget to nugget and from setting to setting, but the general ZVT gain is clear; it is mostly distributed between 0–40% increases, and even higher.
It should be noted that the GPZ 7000 Normal Ground Type is not equivalent to the GPX 5000 Normal Type. Simply put, the GPZ 7000 Normal Mode behaves most similarly to the GPX 5000 Normal Mode (or the Sharp Mode) when using a monoloop coil, but the GPZ 7000 typically has lower ground noise in General Gold Mode than the GPX 5000 does when using a monoloop. When the GPZ 7000 uses High Gold Mode with Normal Ground Type, it will have slightly more ground noise compared to the GPX 5000 using a Monoloop coil and Normal Ground Type.
Default Settings
Significant improvements on the GPZ 7000 compared to
with GPX 5000 for most gold prospectors
likely lies in the use of default settings " High Yield plus Difficult" when compared to the most commonly used settings on the GPX 5000 on flat mineralized soils average (Australia), namely " Fine plus monoloop." This setting
shown as a red circle in figure 3.
GPZ 7000 Gold Mode and Soil Type
Gold Mode
High Yield
High Yield mode is more effective for medium- or small-sized nuggets. The transmitted field reverses polarity (N-S or S-N) three times more often than in General mode.
General
General Mode is better for detecting large or medium-sized nuggets, although some very small and shallow targets may be missed.
Extra Deep
Extra Deep mode is better for detecting in highly mineralized soil (soil that produces more audio signals than average). However, this mode is not as sensitive as General or High Yield modes to very small nuggets.
Soil Type
Normal
The Normal setting should only be used in soil with low mineral content. It provides the best depth, but at the cost of significantly more ground noise. Normal plus High Yield is only suitable for soil types with low mineralization, but it can find small nuggets
Difficult
Hard Mode is best for average mineralization (Australia). This, along with High Yield, is likely to yield the highest number of nuggets for average mineralization and is the default setting.
Severe
MM.I Severe Mode is ideal for the most mineral-rich soils (where audio signals from the ground on other settings are impractical to use). This setting is not recommended for searching for very large, deep nuggets.
Saturated Soil
In all of the above settings, it is recommended to swing the coil about one inch or more above the ground if the soil is considered saturable (VRM). Saturable means that the detector will achieve good ground balance if the coil is raised and lowered to about a few centimeters above the ground, and for the most saturable soils, up to a few
centimeters, but not if the coil is shaken up and down to
lower altitude than " height limit" this is saturated
(for example, all the way to the ground surface). This will be discussed further
details below.
Saturated Soil
The manual teaches you how to do it, but
here are some insights into what happens.
Once the detector is turned on, it will calibrate itself
itself to the ground within seconds of moving the coil
get close to the ground (see important tips below) and press the button
Quick-Trak trigger. This quick initial calibration involves a few
different aspects of the detector being calibrated, not just
to the normal ground balance.
During further searches, the soil balance was
continuously track or ' renew' It continuously tracks or “updates” the balance
soil balance fairly quickly, but other parameters
calibrated during the initial soil balance is updated with
slower. Therefore, if you happen to calibrate
initially in an unusual location (e.g. too close to
with metal targets or over unusual ground areas),
This initial calibration may be inaccurate, and this will
causes additional audio signals when detecting. This is
occur due to slow calibration updates
it takes longer to become more accurate
according to normal conditions (rather than the initial conditions)
unusual).
Soil Balancing - IMPORTANT
The best way to initially balance the ground after turning on the detector by pressing the Quick Trak trigger is to swing the coil in typical search mode from side to side at the expected height above the ground surface, for example, 2-3 cm, or according to the soil saturation level. A slightly faster forward motion than normal walking will help cover as many different soil types as possible in the first 10 to 12 seconds. It's important to remember not to balance the ground with the coil up and down when first turning on the detector. Use the up and down motion only if necessary to balance the ground later.
Reset Land Balance
If you suspect your detector is producing an unexpected ground signal level, turn it off, then back on, and perform a ground rebalance. Typically, this time, your detector will calibrate correctly after powering it back on.
If your detector is still producing unexpected ground signal levels, select " Quick Start" on the Detect page, and then select it " Reset Audio and Detector settings" when prompted. The guide will ask you to rebalance the land.
Shallow Land
When searching in shallow ground that has previously been well detected and has been detected with GPX 5000, it's likely that all the large gold nuggets have been found, as they're easily detected at shallow depths, leaving only smaller pieces remaining. Therefore, in locations like these, only operate the GPZ 7000 in High Yield mode, and avoid Extra Deep mode, as this is less effective at detecting small gold nuggets.
To find larger nuggets deeper down, you need to search deeper. In general, many of the most famous gold fields frequently detected with the GPX 5000 tend to be shallow (though not all are), while deeper fields are usually less well-known because they have fewer nuggets (especially small/medium nuggets) found in the field overall.
the field.
Saline Ground
Although the GPZ 7000 does not have a salt detection setting' Specifically (for satin soil), the best Gold Mode setting for saline soil is Extra Deep.
Although the GPZ 7000 does not have a
specific salt detection setting (satin soil),
the best Gold Mode setting for soil
is Extra Deep.
The Difficult and Severe settings are much less sensitive to spatial differences in ground balance conditions than the Normal setting. In the Difficult or Severe setting, the optimal ground balance setting does not change from meter to meter as you pass the coil over different ground, whereas in the Normal setting, the optimal ground balance setting does.
Optimal soil balance varies more in different soil locations, even if only a few centimeters apart.
Additionally, the soil saturation level (VRM) is significantly lower for “Difficult” or “Severe” conditions compared to “Normal.” Mnelab holds a patent for the soil balancing method for “Difficult” and “Severe” conditions.
Simply put, standard soil balancing methods and scientific literature assume that the VLF (sine wave) soil VRM signal—which differs from the transmitted signal and is referred to as the “resistive” signal—has the same relative magnitude for all frequencies that ' resistive, ' has the same relative magnitude for all frequencies
transmitted. The GPZ 7000’s Normal ground balance method, and all PI ground balance methods in detectors prior to the GPX 4000, assume that all soils behave this way. However, the reality is that soils do not have the same resistive VRM signal for the various transmitted VLF frequencies.
Conversely, if the resistive component of the VRM is measured and plotted on a graph with the magnitude of the resistive signal on a linear Y-axis, compared to a logarithmic frequency scale on the X-axis, the graph is nearly flat but slightly tilted from the horizontal. A graph with a sloping straight line plotted on a linear Y-axis compared to a logarithmic scale
of the variables on the X axis is called ' of the variable on the X-axis is referred to as “log-linear.”'.
The relative slope of the graph varies for different soil locations, sometimes significantly even over short distances, sometimes almost completely even over long distances. Hot rocks have a different slope compared to the soil matrix in which they are buried; this is why they can be detected.
Frequency in kHz (logarithmic scale)
In Figure 4, the X-axis is the frequency in kilohertz plotted on a logarithmic scale. The Y-axis is the magnitude of the VRM resistive component measured using a VLF metal detector with a variable transmission frequency. The standard (old) model is a horizontal line with zero slope and is called ' log-uniform', while in reality, the soil exhibits a log-linear resistive VRM response. The examples shown are enlarged.
enlarged for illustrative purposes.
The relative variation in the slope of the log-linear soil resistive component causes the VRM signal to decrease following rapid changes in the direction of the transmitted field become variable. This is shown in figure 5.