User's Manual

DIGITALCONTROLINCORPORATED
DigiTrak Falcon F5
®
Operator's Manual 69
AppendixC: Projected Depth Versus Actual
Depth and the Fore/Aft Offset
What Happens When the Transmitter Is Steep and Deep
The signal field emitted by the transmitter consists of a set of elliptical signals, or “flux lines”. The flux lines
indicate the position of the transmitter. When the transmitter is level with respect to the ground, the locate
line (LL) is directly over the transmitter, the depth displayed on the receiver is the actual depth, and the locate
points (FLP and RLP) are at equal distances from the transmitter. The location of the LL is found at the
intersection of the ground and the horizontal component of the flux field; the FLP and RLP are found where
the vertical components of the flux field intersect with the ground. Some of the horizontal and vertical
components are identified below by short yellow lines.
1. RLP
2. LL
3. FLP
Side View of Flux Field and Geometry of FLP, RLP, and LL
Due to the shape of the transmitter’s signal field, when it is at a pitch greater than ±10% (±5.7°) and/or a
depth of 4.6 m or more, the position of the locate line will be some distance ahead of or behind the
transmitter’s actual position. In this case, the depth displayed on the receiver becomes what is called the
projected depth. The transmitter’s distance ahead of or behind the locate line is called the fore/aft offset.
The projected depth and fore/aft offset must be accounted for when the transmitter is steep and/or deep. See
Table C1: Determining Actual Depth from Displayed (Projected) Depth and Pitch and Table C2: Determining
Fore/Aft Offset from Displayed (Projected) Depth and Pitch to determine the actual depth and fore/aft offset
when you know the displayed (projected) depth and pitch of the transmitter.