KROHNE BM 102 Handbook - Manual (Page 12)

12 BM 102
Probes: entanglement, straightness and tank bottom clearance
Rigid section length of single
and twin cable probes
Cable diameter
Rigid section length
Single cable
Ø4mm or 0.15”
40mm or 1½”
Ø8mm or 0.15” 200mm or 8”
Twin cable
Ø4mm or 0.15”
40mm or 1½”
• Cable probes must be straight once inserted into the tank. They must also be far from other
objects (e.g. mixers) to avoid entanglement.
• In order to maintain the gauge’s operating characteristics, it is recommended to avoid touching
the tank bottom with the counterweights (for cable probes) or probe end (other types).
Objects (discontinuities) inside the tank that influence the probe’s EM (electromagnetic) field
Install the gauge far from protruding objects such as:
• Heating tubes,
• Sudden changes in tank cross-section,
• Tank wall reinforcements and beams,
• Weld lines and dip-stick pipes, etc...
TDR gauges generate electromagnetic (EM) fields when a measurement pulse is emitted. This field
is affected by any nearby discontinuities and these will weaken and potentially block the emitted
pulse. A minimum distance is recommended depending on the probe type to be installed. See the
table on the next page for recommended free space dimensions.
Alternatively, the fitter may use a reference chamber or stilling well. However, the chamber walls
must be smooth (i.e. no visible weld lines), straight and vertical to maintain the pulse strength and
gauge accuracy.
For clean applications only :
Coaxial (type 3) probes may be used close to or touching objects or walls as the EM field generated
by the probe is contained within the probe’s outer sheath (refer also to the EM field sizes/free area
given in the figures on the next page).