Discrimination Mode - Fisher Labs F 75 User Manual

Discrimination Mode

The Discrimination Mode is used to eliminate trash metal objects from detection, e.g. nails,
aluminum foil, or pull-tabs. The searchcoil must be in motion for metal objects to be detected.
Discrimination incurs some loss of sensitivity to small or deep objects.
The F75 discrimination system is much improved over conventional discrimination systems,
and may function quite differently than other discriminators you may be accustomed to. In
older systems, the apparent sensitivity decreases as discrimination level increases. The F75's
sensitivity may increase as discrimination increases, depending on the process number and
notches being used. Therefore, do not use the discriminator to control sensitivity. First set the
discrimination level and notches to establish objects to detect or eliminate; then adjust
sensitivity downward to eliminate interference, or upward to "work into the noise," if preferred.
SENSITIVITY
This controls the signal gain, and is adjustable from 1 to 99. Unlike the All Metal modes, the
Discrimination mode is designed to operate silently. If you hear noise when there is no metal
present or when the searchcoil is not in motion, reduce the Sensitivity setting until the machine
goes quiet. NOTE: there is no interaction between the sensitivity settings of the All Metal
and Discrimination Modes.
The sensitivity system has two stages, 1-29 (low gain), and 30-99 (high gain). As you lower
sensitivity and cross the transition from 30 to 29, you may notice the background noise
increase. You may need to adjust to a setting of 29 or less to silence electrical interference, or
to prevent overload on highly mineralized ground or in salt water. You may also notice a shift
in the ground balance setting over difficult ground conditions as you cross this transition.
DISCRIMINATION LEVEL
This is adjustable from 0 to 65, and controls the range of objects to be eliminated from
detection (discriminated out or rejected). Objects with numeric values below the selected
discrimination level will not be detected. NOTE: the numerical range that pertains to each
class of object is printed at the top of the visual display. To eliminate iron, a setting of 15 is
usually about right. A setting of 65 will eliminate aluminum trash and zinc pennies, but nickels
will also be lost, unless you notch-in nickels with the NOTCH feature.
To use DISC LEVEL
1. Highlight DISC LEVEL using the MENU button.
2. Rotate the SETTINGS knob.
As you rotate the knob, a number between 0 and 65 appears.
3. Press MENU when you reach the desired target discrimination value.
• If you do not press MENU, and let the display time-out, the last displayed value
will be stored as the discrimination value.
• All targets, up to and including the value selected, will be eliminated from
detection, unless notched-in.
5. A slash will appear over the target words being eliminated. Notice that two slashes
can appear over each word. The left slash represents the bottom half of the range; the
right slash represents the top half of the range. When you select a value within any
range, the slash will appear, even though all values within that range might not be
eliminated from detection. To recall the discrimination setting, press the MENU button
until you enter the DISC LEVEL feature.
Comprehensive Operating Manual & Guide to Metal Detecting
F75
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