KROHNE BM 70 M Series, Installation And Operating Instructions Manual

Page: 13 / 110

BM 70 M 13
4.8 Digital input
The digital input (for electrical data: see Section 4.2) can be used for temporarily "freezing"
measurements or for carrying out a hot start. It is only available in the "Ex-e current output
HART
®
" version.
The "freeze" function can be used to blank out larger, temporary interferences, e.g. very slow
agitator, slide gate, ball valve in the stilling well. The last measured values in each case are
present at outputs I and S, and in the display. The digital input is also taken into account when
the empty-tank spectrum is being recorded (totalizer does not continue). Marker 6 in the display
indicates that the digital input is active in the "freeze" function.
The function of the digital input is set as standard to "freeze". To switch the
function to "hot start" or to deactivate it completely, the setting will need to be
changed in the Service menu of the BM 70 M.
5 Measuring accuracy
5.1 Reference conditions
Temperature +20°C / +68°F
Pressure 1013 mbar abs. / 14.5 psia
Air humidity 65%
Highly reflecting product (e.g. water) with calm surface
Tank diameter
> 5 m / 16.4 ft
Mounted at least 1/7 x tank height away from tank edge (BM 70 M: 1/5 x tank height)
No interference reflections inside the radiation lobe (± 6...9°; see Section 6.1.1)
5.2 Error of measurement
Since the measuring process primarily determines distance, measuring accuracy can only be
specified as a function of the distance. For that reason, all figures given in this Section 5 refer to
the measured distance.
Only with antenna type 4 (200 mm / 7.87") or stilling well 100 - 200 mm dia. (4 - 8")
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
0 5 10 15 20 25 30 35 40 m
Distance to flange
Accuracy
1
Block-
distance
± 0.01 %
± 2 mm (0.04")
±
20
mm
30
...
16 33 49 66 82 98 115 3
131ft
-0.4
-0.32
-0.24
-0.16
-0.08
0
0.08
0.16
0.24
0.32
0.4
inch mm
0.48
-0.48