KROHNE BM 70 M - Manual (Page 54)

54 BM 70 M
8.6.13 Time constant and tracking speed
Fct. 3.5.3 TIMECONST.
• New measured values are damped (filtered) with the time constant so as to avoid abrupt
changes in measured values and thus also in the current output I and the display.
•
Setting range:
010 - 100 Sec (BM 70 M)
• The tank bottom must supply a measurable reflection
signal, so the method cannot be applied e.g. when a dished bottom is involved.
• Default value and recommended setting:
030 Sec (BM 70 M)
Fct. 3.5.4 TRACING.VEL.
To avoid faulty measurements, the BM 70 M places a symmetrical "plausibility range" around the
last valid measured value in which the next measured value is expected. Measured values
outside this range are identified as invalid and are suppressed.
If no valid measured value is identified, the BM 70 M enlarges the plausibility range with the
tracing speed (Fct. 3.5.4) until a valid (plausible) measured value has again been found.
The measured value for level/distance cannot change at a faster rate than the set tracing speed.
• Under Fct. 3.5.4 the maximum rate at which the level can change in the tank should be set as
the minimum value.
• Setting ranges:
0.01 - 1.00 m/min (if Fct. 3.1.1. Unit m/ cm/ mm)
0.03 - 3.28 ft/min (if Fct. 3.1.1. Unit inch/ft)
• Default: 0.1 m/min (BM 70 M)
• See also Sect. 8.8 (error message: NO M.VALUE)
8.6.14 Multiple reflections and block distance detection
Fct. 3.5.5 MULT.REFL
Multiple reflections frequently occur in storage tanks with an extremely calm surface, typically
when the BM 70 M is mounted on a dome or centred on a "dished cover", or the vessel is fitted
with a flat or only very slightly convex head.
Such multiple reflections tend to simulate lower-than-actual levels. In such cases, activate the
multiple reflections identifier, and see also references in Sect. 8.8.
• NO (default)
Measurement without identification of multiple reflections.
• YES
Measurement with identification of multiple reflections.
A better solution, however, is to change the mounting location of the BM 70 M so as to prevent
the occurrence of multiple reflections in the first place, or at least to diminish the strength of the
multiple reflections (see Sect. 6.1.2).
To ensure satisfactory identification of the first measured value after the BM 70 M has been
switched on, always carry out measurements with the "empty spectrum" (Fct. 3.5.2) when the
"multiple reflection identifier" is activated, see Sect. 8.6.12.