Tracking, Motion, and Sweep Speed – Part 1

With the introduction of the Motion settings on the GPX series detectors, there has been a bit of confusion among some users as to what it actually does, and also how it differs from the Tracking speed selection. I’ll start with explaining Tracking speeds.

Tracking

The Tracking Speed function controls the rate at which the automatic ground balance senses the ground, to make adjustments when required. The speed you select should be dictated by how variable the soil mineralisation is, but also how fast you are sweeping the coil. If you are in highly variable ground, but are working at a snails pace, then the detector will most likely keep up with the changes in the ground using a Medium Tracking speed. However, if you are patch finding and swinging at a faster pace, you may require a Fast Tracking Speed. This may be necessary even in slightly variable soils, as with a fast sweep you are traveling faster across the ground, essentially reducing the time between ground changes. The instruction manual states: “The preferred Tracking speed is the slowest speed which keeps up with the variability of the ground mineralisation.”  To put that another way, don’t use a Tracking Speed that is faster than needed, i.e. the Fixed GB is best, then Slow Tracking, Medium and Fast Tracking as a last resort.

The coil type being used can also change the required Tracking Speed, as ground that appears quite mineralized and variable to a Mono coil, may be fairly easy to work using a DD coil. The timing being used also has an affect, so it can be a fine balance with selecting the right combination in different ground types. In practical terms, after selecting your coil, timing, and search mode, you should ground balance and start to detect in Fixed. If you find that you are re-ground balancing too often, try detecting in Slow Track. If the level (or variability) of the mineralisation is still not being balanced out, then select the next speed and try again. Starting from extreme mineralisation through to mild, here are some recommended setting combinations:

From #1 EXTREME SOIL to #6 MILD SOIL

1. DD coil, Fast tracking, Normal timing

2. Mono coil, Fixed GB, Sensitive Smooth timing

3. Mono, Fixed GB, Fine Gold or Enhance timing (suits a variety of goldfields)

4. DD, Medium Tracking, Normal or Sensitive Extra

5. DD, Fixed GB or Slow Tracking, Sharp or Sensitive Extra timing

          6. Mono coil, Fixed GB, Normal or Sensitive Extra timing

So what does Motion do?

The Motion control adjusts the duration (or width) of the internal filtering. You can think of the filter as a gate. In the detector, everything sensed by the coil is passed through the gate, including EM noise, ground and target signals. In simple terms, the Motion control adjusts how wide (or for how long) the gate is opened - the faster the Motion setting, the more the gate is opened, so more information is allowed in. So in quiet conditions, a Medium or Fast Motion speed is the preferred setting, as it allows you to sweep a little quicker and not miss targets. However, in a lot of areas, a Fast Motion speed (wide open gate) is going to let in more atmospherics (airborne interference or E.M.I.), making the detector threshold unstable, which in turn may mask a faint signal response.

A Slow Motion setting keeps the gate open for a shorter amount of time, reducing the amount of interference that can get in. This results in a much smoother threshold, but a target’s response will also be reduced, so a slow sweep speed is critical to ensure that the detector can produce an audible target signal. Slow Motion gives a good compromise between stability and target recognition, provided the coil is kept nice and parallel to the ground, and slow even sweeps are maintained. The Very Slow Motion option provides a very smooth threshold, and allows the Rx Gain to be slightly increased, so is ideal when searching for deeper targets. However, due to the gate only being opened for a very short duration, the user must employ a very slow sweep speed, so is best reserved for working small known gold producing areas or “patches”.

The coil being used also has a bearing on the correct Motion setting to use. The Slow and Very Slow options will benefit greatly from the sharper target response that is generated by a Monoloop coil. Double D coils have a weaker signal compared to a Monoloop due to the physical distance of the Tx & Rx windings, so will benefit greatly from the gate being open that bit longer. If you are using a Double D coil, you should try to use Medium Motion, even if it means reducing the Rx Gain slightly. If you have to use Slow with a DD coil, due to excessive interference, then make sure you're swinging at a slow even pace. Try to avoid using Very Slow with a DD coil, as you could easily miss a small target.

Coil Sweep speeds will be discussed in Part 2.

Nenad Lonic 

Technical Sales Representative

Minelab Electronics