CT33 User Manual v. X1.0 34
13.3 Using duct sondes to locate duct blockages
Choosing the right sonde and receiver probe:
10kHz or 33kHz sondes and SA43 rod are optimal to use with non-conductive ducts. 512Hz sondes and
SA05 probe are optimal for cast iron or stainless steel ducts, though they can be used with non-conductive
ducts as well. Regardless of sonde size or frequency, all sondes are traced similarly. It is advisable to
continuously follow the sonde signal as it travels in the duct.
Task: Duct route or possible blockage needs to be
located above ground or inside a wall.
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Approximate location: Hold the CL43 in 45° angle. Scan
left and right with the probe and move to the direction
where the signal in average gets stronger. Approximately
1m location accuracy can be achieved by this method.
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Exact longitudinal location: Hold the CL43 vertically and
follow the sonde signal as it progresses in the duct. To
define the exact longitudinal location of the sonde,
pinpoint the signal minimum line. It runs transversely (in
90° angle) against the direction of the duct & sonde. Mark
the minimum line to ground for a few metres.
