KROHNE BM 70 M User Manual
Page 40
40
BM 70 M
8.5.1 Level
measurement
(example)
Tank height
(Fct. 3.1.1)
6.00 m
Antenna extension
(Fct. 3.1.4)
0.20 m
Block distance
(Fct. 3.1.2)
0.70 m
Response threshold or
maximum measurable level =
5.30 m (calculated from lower
reference point)
= tank height - block distance
(Fct. 3.1.1) (Fct. 3.1.2)
= 6.00 m - 0.70 m
Function I (Fct 3.3.1)
LEVEL
Range I (Fct. 3.3.2)
4 - 20 mA
Scaling 4 mA (Fct. 3.3.3)
0.00 m, equivalent to 4 mA
Current output I
Scaling 20 mA (Fct. 3.3.4)
5.00 m, equivalent to 20 mA
Function S (Fct. 3.6.1)
LEVEL
Type S (Fct. 3.6.2)
LOW (= below threshold)
Threshold (Fct. 3.6.3)
5.00 m
Switching output
Hysteresis (Fct. 3.6.4)
0.10 m
Function, display (Fct. 3.2.1)
LEVEL
Display
Unit, length (Fct. 3.2.2)
m (meters)
Note:
Display and outputs can also be used for different measured variables,
e.g.: display for conversion, current output I for level, and switching output S for
error messages.
The value for Scaling 20 mA should not be greater than the response threshold.
8.5.2 Volume measurement (example)
•
In order to be able to measure volume with the BM 70 M, a conversion table (volume table)
needs to be compiled with the PC-CAT program (see Sect. 8.12).
•
By means of the volume table, various levels are allocated to specific volumes previously
calculated or measured out.
•
In the case of non-symmetrical tanks, e.g. tanks with dished bottom, the accuracy of volume
measurement will depend on the number of set "level/volume pairs". The maximum number of
pairs (points) that can be set is 50; the volume is linearly determined (interpolated) between 2
points.
In the following example, 4 data pairs have been programmed:
Volume table
Unit volume (Fct. 3.2.3): m3
Point Level Volume
1
0.00 m
0.25 m³
2
0.25 m
0.70 m³
3
0.50 m
1.40 m³
Set table (PC-CAT)
4
5.30 m
16.80 m³
Tank height (Fct. 3.1.1):
6.00 m
Antenna extension (Fct. 3.1.6)
0.20 m
Block distance (Fct. 3.1.2)
0.70 m
Response threshold,
maximum measurable level
= 5.30 m, equivalent to a
volume of 16.80 m ³
(calculated from lower
reference point)
= tank height - block distance
(Fct. 3.1.1) (Fct. 3.1.2)
= 6,00 m - 0,70 m