Instruction manual

nearby with an electric drill or similar tool can also generate sufficient magnetic
fields to disturb the detector.
Wobble (rhythmic side to side or up and down motion) causes the Detector to
display increased noise on the LED display. If the wobble is severe enough, it will
cause the Detector to falsely signal a tag. Check a Detector mounted on a
gurney or otherwise mounted in a less than rigid manner for excessive wobble.
Wobble it to the extent that passing fish through might cause it to wobble while,
at the same time, observing the LED display. If the displayed noise is too high,
i.e.: nearing or exceeding Tag Threshold, the setup will have to be made more
rigid.
If fish are hitting the inside of the tube quite hard and causing false positives,
change how fish are fed in. Diminishing both how hard the fish hit the tube and
how much the Detector wobbles will reduce the problem. Also optimize the
speed of fish traveling through the tube to maximize the signal strength so that
the Sensitivity may be decreased.
Magnetic sand and dirt picked up on the fish from the beach or fish holds on
boats, as well as fishhooks look the same to the Detector as CWTs. The only
solution is to keep the fish as clean as possible. Place a tarpaulin under the fish
if it is necessary to put them on ground, and rinse off any sand before putting
them through the Detector. Fishhooks must be removed.
Optimizing Conditions
All of the problems discussed above should be addressed if there are any
difficulties sampling. A combination of all of them acting in a minor way may not
allow any one to be obviously notable, but the combination can cause repetitive
false signals. If the Detector is mounted as rigidly as possible, has good water
flow to minimize friction, and clean fish are fed carefully, the Detector works very
well.
Testing Sensitivity
The CWT Detection Standard (available from NMT) has a standard length tag in
the center of the "plug". Pass this through the middle of the Detector at the same
speed as fish are traveling to confirm that a CWT will cause a signal at least two
lights above threshold.
R-Series Instruction Manual 37