KROHNE BM 100A Handbook - Manual (Page 39)

Handbook BM 100 A 39
3.4.6 BM100A TDR level meter characteristics
This subsection explains :
• the four principle configurations for setting up a measurement scale and what the user should
be aware of in each case
• what happens when the tank is full or empty.
• what are level and interface thresholds and how to modify them,
• what happens when one product is measured in interface mode
The measurement scale: four possible configurations for analogue current output - with
“Level” selected in function 1.3.1 (Function I.1)
1 True tank height
2 Measurable height
(probe length), L
1
3 Non-measurable
zone
4 Hold distance (user
function 1.1.2)
5 Minimum dead zone
value:
(Fct 1.5.3 – Fct
1.1.2)
6 Detection delay
(user function 1.5.3)
7 Active measurement
zone
Note that 4mA is set in user menu function 1.3.3 and 20mA is set in user menu function 1.3.4.
As can be seen above, there are 4 principal scale configurations for measuring level:
Configuration A
Parameters :
Function 1.1.1 = Probe length, L
1
(excluding counterweight*)
Function 1.3.3 (4mA) = 0.0 m/mm/in./ft. units defined in 1.2.4 (for 4 mA)
Function 1.3.4 (20mA) = Probe length, L
1
– Hold distance (maximum value)
The configuration used in Quick Configuration Example Procedure 4 in section 3.4.3. When the
gauge reaches the minimum and maximum outputs then the measurement will freeze as the tank is
now considered to be empty or full respectively.
Configuration B
Parameters:
Function 1.1.1 = Probe length, L
1
(excluding counterweight*)
Function 1.3.3 (4mA) = 0.0
Function 1.3.4 = Probe length, L
1
(excluding counterweight*)
The top of the scale is set to gauge flange facing. The measurement will freeze in the top dead zone.
Warning: danger of overflow!
It is impossible to detect product reflections in the top dead zone!
Configuration C
Parameters:
Function 1.1.1 = True tank height
Function 1.3.3 (4mA) = 0.0
Function 1.3.4 (20mA) = True tank height (1.1.1) – Hold distance (1.1.2)
Has the top of its scale below the top dead zone but the bottom of the scale is below the end of the
probe (on the tank bottom). As TDR is a contact technology, the display will freeze at a level above
the 4 mA limit when product level drops below the probe end.