KROHNE BM 702 EN - Manual (Page 15)

Installation and operating instructions BM 702 (06/04) 15
Explanatory notes
Tank height
The tank height (Fct. 3.1.1) for the BM 702 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 702 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 702 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).
By pressing the two upper keys (
→ and ↑) or the two lower keys (↵ and ↓) at the same
time, the 0% setting (= 4 mA) or 100% setting (= 20 mA) can be programmed according to
the actual level (see page 9).