KROHNE BM 700 EN - Manual (Page 12)

Page 12 BM 700 Installation and Operating Instructions
Explanatory notes
Tank height
The tank height (Fct. 3.1.1) for the BM 700 is defined as the distance between the
top edge of the tank connecting flange and the bottom reference point. The bottom
reference point is that “point“ in the tank on which the microwaves of the BM 700 hit
and from which they are reflected. This may be the tank bottom (symmetrical tank
with flat bottom) or the non-horizontal part of the bottom (e.g. tank with dished
bottom) or an additionally fitted plate. The BM 700 cannot measure below this point
(“sump“ in the tank).
Note: When the tank is completely empty and the tank bottom provides good
reflections (flat, not dished bottom!), the tank height can also be automatically
determined with the aid of Function Fct. 3.5.1 AUTO TANKH. Before confirming,
check carefully that the proposed tank height is plausible!
Block distance
The “block distance“ function (Fct. 3.1.2) defines a zone below the top reference
point in which measurements are not meant to take place. The value should be at
least 10 - 20 cm greater than the length of antenna+antenna extension, or at least 20
cm in the case of the Wave-Stick.
Signals within the block distance are suppressed; a rise in the tank filling above this
limit (response threshold) will lead to a measuring result corresponding to a distance
= block distance, when Fct. 3.5.6 BD-DETECT. is switched on.
Scaling of the current output
The scaling of the current output (Fct. 3.3.3: level 1 = 4 mA ; Fct. 3.3.4: level 2 = 20
mA) should if possible lie within the measuring range (between bottom reference
point and response threshold).
Sump non
measurable
zone
tank height
(Fct. 3.1.1)
Fct. 3.1.4
upper reference point
(top edge of tank connecting flange)
block distance (Fct. 3.1.2)
response
current output
20
mA
Imax
(Fct. 3.3.4)
4
Imin
(Fct. 3.3.3)
lower reference point
(tank bottom / datum point)
+
+
+
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+
+
+
+
+
+
+
+
+
+
+
+
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+
+
+
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+
Fct. 3.1.5
threshold
measuring
mA
[e.g.: 5.30 m]
[e.g.: 0]
[Bsp: 0]
[e.g.: 0.6 m]
[e.g.: 0.4 m]
[e.g.: 4.0 m]
range