Density Meter LB 444 SECTION 6. BASICS OF DENSITY MEASUREMENTS
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6.4 Automatic Measuring Time Switchover
To obtain a quick update of the measured value in case of sudden density
changes, you can activate the automatic measuring time switchover (rapid
switch-over in the Parameter menu, see page 18).
The smallest value that can be entered is 8 s.
If a sudden density change occurs which is higher than the entered threshold
(Sigma), the entered time constant is reduced to 1/10 of the original value, but
not less than 0.8 s. Thus, the output signal adjusts much quicker to the new
density value. The changed time response of the output signal is illustrated in
the diagram below.
Res ponse
-3 2 7 12 17 22 27 32 37 42 47 52 57 62 67 72 77 82 87 92 97
0
20
40
60
80
100
T in s
Display and output signal in %
Output signal without
fast response
Density
Output signal
with fast
response
Figure 29: Response
When the rapid switchover is in effect, the measurement first works with the de-
fined basic time constant. If sudden density changes occur which exceed the
Sigma band, the system switches to the 10-times lower time constant and the
reading and the output signal can follow the density change much quicker. At
the same time, the statistical variations increase by a factor of about 3. When
the density value becomes stable again, the system automatically switches back
to the longer basic time constant after a period of time that corresponds to the
basic time constant.
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