User Guide

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7
LOCATING BY THE NULL METHOD - IN THE AUTOMATIC MODE
The receiver will always power up in the AUTOMATIC PEAK MODE OF OPERATION. Turn on the receiver and rotate the
large knob until the desired level of sound is being heard. In the Auto Mode, the knob is a "VOLUME" control. Push the
NULL button for NULL operation. A little flag at the lower left corner of the display will point to NULL.
Move out 5 to 10 feet from the transmitter and walk a half circle around transmitter until the bar-graph display starts to
increase. At some point, the bar-graph will drop to a small value and then increase. Directional arrows are also present
that will indicate what direction is needed to find the conductor. As the receiver moves past the null point, the directional
arrow will change and a different tone will be heard. Each time the conductor is crossed, the directional arrow will change
and the sound being heard will also change. The numerical signal strength meter will read absolute signal and it will be at
a maximum number, even though the receiver is in the null mode of operation. In the Automatic Null Mode, the receiver will
provide direction to the conductor with left/right arrows on the display so the receiver must be at right angles to the con-
ductor path in the Auto Mode.
LOCATING BY THE NULL METHOD - IN THE MANUAL MODE
Locating in the manual mode allows the operator to take control of the receiver sensitivity. The large knob that was the
loudness control in the auto mode is now the sensitivity control.
Change the receiver to Manual and push the Null switch for Null operation. A flag will point to the word NULL on the lower
left corner of the LCD display. In the upper left corner of the display, a numerical read out will appear. This 0 to 100 read-
ing will indicate the position of the sensitivity control as it did in the manual peak mode.
The method of locating a Null in the manual mode is identical to the automatic mode except the operator is required to adjust
control on the receiver. The left-right guidance arrows will not be present on the display, so the antennas do not have to be
at right angles to the conductor path. The tone pitch will remain constant on both sides of the conductor.
As shown in Fig. 6, a large signal will be present on both sides of the locate and a minimum signal will be found directly over
the locate. The sensitivity control setting controls the display response. Using a higher sensitivity setting can sharpen
broad null readings. They may be made wider by reducing the sensitivity.
DEFINITION OF A NULL - See Fig. 6. A high signal reading is found on both sides of the conductor, and a loss of signal
is found directly over the conductor.
Figure 6
TRANSMITTER
The Digi-7 transmitter has both INDUCTIVE and CONDUCTIVE methods to apply signal to the conductor to be traced.
On the faceplate, two rocker switches are located in the upper right hand side. One switch turns the transmitter on
and off. The second switch is used to operate in the Automatic or Manual mode. This switch also allows the operator
to change the direct output tap in the manual mode. The power control knob is used to control the output level for
extremely long or deep locates. Most locates can be made with the lowest power setting.
When the transmitter is turned on, the TAP # window will show a self-test mode. If nothing is plugged into the output
jack, the letter "A" will then appear on the numerical display. This indicates the transmitter is set up for Inductive
Antenna Operation. See INDUCTIVE TRACING on page 8 for set up and use.
With the direct output cable assembly or Inductive Coupler plugged into the direct output phone jack, the transmitter
switches from the Inductive Antenna mode to the Conductive mode of operation. In the Automatic mode, the transmit-
ter will match the output impedance and select the right tap that is needed for the best trace. In the Manual mode, the
tap switch must be pushed until the tap # desired by the operator appears in the numerical display. Manual mode can
also be used for mismatching the transmitter to the line being traced to correct for a broad peak reading. See page 8
DIRECT OUTPUT
With the direct output cable assembly plugged into the transmitter, connect the red lead clip to the conductor being
traced. Insert the ground rod in the earth and clip the black lead clip to it. It is important to obtain the best ground
possible. This may be within inches of where the transmitter is connected, or several feet away.
HINT: Pouring water on the ground rod can improve the ground connection in dry soil. A FIVE-GALLON CONTAINER
OF WATER IS A VERY IMPORTANT ACCESSORY TO HAVE WITH YOU.
Turn on the transmitter and have the power control at low power. If the transmitter is in the automatic mode, the
numerical display will set itself to the correct tap number for the best locate. If the soil conditions or power level change
while locating, the transmitter will track that change. If for some reason manual selection of the output is required, the
following guidelines should be noted.
MATCHING THE TRANSMITTER IMPEDANCE IN THE MANUAL MODE
In wet soil, tap # 1. In average soil or medium dry, use tap # 2. In very dry soil conditions, or with the ground plate
on asphalt or concrete, use tap # 3. Tap # 4 & 5 are used for mismatching the impedance. If unsure as to what tap num-
ber is needed, make your output connection and turn the transmitter on. Set the tap switch to tap 1, 2, or 3. Move out
several feet away from the transmitter, turn on the receiver and lay it down where the LCD (liquid crystal display) can
be seen while standing at the transmitter. Go back to the transmitter and find the tap number that provides the high-
est numerical number on the receiver display. This will provide the most signal on the line for the best trace.