5 Operation
5.8.3
Sonde Location
This is used for locating a Sonde only. A Sonde is a transmitting coil and the signal
radiates in a different manner than that of a line (see diagram b).
Due to this construction, the Sonde gives a different “Peak” pattern (see diagram b)
- note that there are 3 distinct peaks - a small peak - a large peak - a small peak.
The Sonde is located under the center of the “large peak”, when locating across the
direction of the Sonde it provides the conventional peak response. Note also that the
Sonde Direction Indicator points across the line of the Sonde when the receiver is
directly over it.
A Sonde is typically used for locating non metallic pipes or ducts. The Sonde operating
frequencies for the 800 series are:
•
VM-810 operating frequency is 83.0775 kHz
•
VM-850 operating frequency is 9.82 kHz
The procedure for Depth Measurement is the same as in line location, but must be
done in the Sonde mode. Depth measurements taken from a Sonde in any mode other
than Sonde mode will be inaccurate.
5.8.4
Using the Sonde Direction Feature to Locate Sondes
Switch on the 810/850 by pressing the ON/OFF button. Then press the button twice
quickly to activate the Sonde mode.
Stand in the approximate vicinity of the Sonde. If the signal strength is weak and
the Left/Right guidance indicator is fluctuating, it means that the Sonde is not in the
expected vicinity. If this is the case pull back the Sonde to a known position, which
may be the point the Sonde enters the pipe, and start the search here.
Rotate the locator until the Sonde direction indicator is pointing at 12 o’clock. Walk in
the direction of the Sonde direction indicator keeping the direction indicator pointing
at 12 o’clock. The locator will lead you in an arc that crosses over the Sonde. The
maximum numerical signal strength and the centerline indicate the position of the
Sonde.
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(a)
(b)