User's Manual

90
80
70
60
50
40
30
20
10
0
RB
ZA
ZB
0 2 4 6 8 10 12 [m]
ZP
Product
reflection
Bottom zone
threshold
14
TI : TK-200SmartRadar Refl. Diagram.
[dB]
08-11-1996 12:31
BA417-1899001-D0
: TK-20000.RD3
:.18739640023
File
SN
7.450
Tank
Zero
Min. Ull
Max. SF.
Antenna zone
threshold
Product zone
threshold
Antenna
position
ZB
0.6 m
Product
peak
Tank zero
Bottom
peak
[m]
Commissioning
Page 24
Figure 3.6 Reflection diagram
Figure 3.7 Bottom reflection and bottom
zone adjustment
The area between antenna zone length and the bottom zone is called "product zone". The product zone
threshold can be set with item
ZP
.
The bottom zone is defined around tank zero. With bottom zone offset (item
BZ
) the position above tank
zero is defined where the product zone ends and the bottom zone begins. The bottom zone extends three
Fourier distances under tank zero (approximately 0.44 m).
The bottom zone definition is important in applications where the bottom can be seen through the product in
the reflection diagram. At a low product level both the product reflection and the bottom reflection will then
be present and the bottom reflection can be the strongest. In that case the bottom zone offset must be set
large enough to make sure that when the tank is emptying the product peak enters the bottom zone first,
before the bottom reflection enters the bottom zone. The bottom reflection peak enters the bottom zone in
the opposite direction and the peaks merge when the tank gets empty.
The low speed of the radar signal through the liquid column
gives the impression that the bottom looks further away than it
really is. When the tank is emptying the bottom appears to
rise. Figure 3.7 gives an example of such a situation. Item
BZ
should be set to a value of 0.6 to 1.0 metres (2' to 3' 4").
When measuring the roof of a (internal) floating roof tank, the
mechanism of searching for a smaller peak in front of a larger
peak in the bottom zone is disabled. By setting the third
element in item
4S
(2 level calculation decision switch) to ‘R’
nd
you can declare the floating roof application.
Reflections beyond the bottom zone are ignored for level
detection. The bottom zone threshold can be set with item
ZB
.