Electronic level sensor
LW2120
23
•
False echoes within the tank offset which affect the measurement and lead to measurement errors
are detected and, where necessary, communicated after the delay time has elapsed (see
parameter [Alert mode delay time]).
•
Take into account agitators and objects in the lower tank section that could cause false echoes.
If the tank bottom is above the desired zero point (e.g. in the case of an inclined tank bottom
with outlet zone):
u
Enter values < 0 (negative values) for the tank offset.
w
The tank offset is added to the displayed process value. This means that the display and switch
point refer to the actual level (e.g. the lowest point of the tank).
A faulty configuration can result in incorrect process values and avoidable error messages.
u
Make sure that the tank geometry parameters are entered correctly.
Upper blind zone / detection threshold:
A
C
E
m
0
mV
0.5
1.0
1.5
2.0
2.5
3.0
0 150 300 450 600 750 900
D
B
Fig. 17: Upper blind zone / detection threshold
A:
upper blind zone
B:
disturbing echo of object
C:
100% (20 mA) of the analogue range
D:
detection threshold
E:
medium surface echo
Nozzles or other objects close to the antenna may cause disturbing reflections. Such reflections
can be blocked out by configuring an upper blind zone (A).
Note: In the upper blind zone, the level is not detected.
u
Make sure that the maximum level is limited, e.g. by using an overflow or by throttling the inlet.
The detection threshold (D) “cuts off” all reflections below the set threshold (in the fig. “Upper
blind zone / detection threshold” to the left of the marked line D). Only reflections that exceed
the threshold (in the fig. “Upper blind zone / detection threshold” to the right of the marked line
D) are evaluated as potential level echoes and included in the further level calculation. Note the
remarks: Detection quality check (
