Fisher TW-7700 manual Depth Accuracy

DEPTH ACCURACY

Depth measurement is a feature of the TW-7700. Accuracy is defined on an ideal target, that is, one that is continuous, a good conductor, and not surrounding by other utilities. There are factors that can cause the operator to question the accuracy of the utility being traced.

Inductive Transmitter Setup

Inductively, only a small portion of the signal attaches itself to the utility. With a weakened signal, trace should be accurate, but depth may not. The conductive method will yield better results.

Low Receiver Signal Strength

When the signal strength falls below 20 – 25%, depth readout may not be accurate. It would be beneficial to move the transmitter to a closer point of contact.

Nearby Utilities

Close, nearby utilities may have some influence on the accuracy of the Depth readout. This is more prone to happen in the higher frequencies where signals can jump to nearby utilities. Switching to a lower frequency can give better results.

Moisture

Ground that is too dry or overly saturated may skew the depth readout.

“T’s”, elbows, or splits in the utility can distort the transmitted signal in that general area.

WARNING: Do not connect output leads to a live (energized) utility. Please prevent shock hazard and equipment damage.

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