Fisher TW-7700 manual Operating Instructions, Initial Scan, Inductive, Conductive, Tracing

OPERATING INSTRUCTIONS

The following instructions are designed for a safe and effective method of line tracing and utility avoidance. Some of the steps may not be applicable in all situations. The underlying guideline is that operator safety must be maintained at all times. Use of safety equipment, extra personnel, and up to date as-built plans should be considered when necessary.

INITIAL SCAN

Set-up Transmitter either Inductively or Conductively

Inductive

Be aware of air coupling, the transmitted signal travelling to the Receiver via the air, not the utility.

Conductive

Connect the ground plate/ground rod assembly to the trans- mitter. Connect the red lead to the non energized utility. Con- nect the black lead to the ground plate/ground rod. Place the plate/rod at a 90 degree angle in reference to the utility. Be sure not to place the wires over any other utility.

After transmitter set-up, move away from the point of con- nection (or Induction) about 25 feet (8 meters). Sweep a circle around the point of connection. Initially, disregard the LEFT/RIGHT indicator and rely on the signal strength readout. Make note of the high readings. These are areas that need to be traced/examined in more detail.

Tracing

After locating the point(s) where the signal strength was the highest, return to that/those points and start tracing your utility. This is where the LEFT/RIGHT indicator is very helpful. Swing the receiver from left to right and lis- ten for the change of tone. When the target is to the RIGHT of the receiver, the tone is pulsed tone. As the receiver gets closer to the target, the pitch gets higher. When the target is to the LEFT of the receiver, the tone is a continu- ous tone. As the receiver gets close to the target, the pitch also becomes higher. When the receiver is over the target, OVER TARGET is displayed on the display screen, and the tone is at its highest peak sound.

Depth Measuring

When an OVER TARGET response is displayed, position the blade of the receiver directly over the utility and place the tip on the ground. Hold the receiver steady, press and hold the DEPTH pad. Depth will be measured to the center of the utility.

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