KROHNE BM 70 M - Manual (Page 56)

56 BM 70 M
Fct. 3.5.7 FUNCT. FTB
•
The tank bottom tracing system is activated under this function:
• OFF
The FTB is deactivated; the device operates in the standard mode.
• PARTIAL
When this option has been selected, the tank bottom tracing system is activated only in the
vicinity of the tank bottom, i.e. at low levels (max. 20% of the tank height but a minimum of 0.6
m). Given higher levels, the normal measuring method is used (reflection from the product
surface). This method is sufficient for most applications with poorly reflecting products.
The parameter EPSILON R (Fct. 3.5.8) must be as exact as possible.
Fct. 3.5.8 EPSILON R
Use this function to enter the relative permittivity.
• Allowable input range: 1.1000 - 8.0000
•
Default: 2.0000
Enter the figure of 2.0000 if the relative
permittivity is not known, as numerous products
have a
ε
R
value ≈ 2. However, expect reduced
measuring accuracy and/or skipping of the
measured value on changeover from tank bottom
tracing to the normal measuring mode
(= evaluation of reflection from the product
surface), see diagram at the right:
8.6.16 Tank type, movement of product surface
For optimum results, data acquisition and evaluation must be matched to typical tank
characteristics: movement of the product surface, rapid or slow changes in the product level,
agitators, etc.
Fct. 3.5.9 TANKTYPE
•
STORAGE T.
Storage tank, still surface, slow rate of change in level
• PROC.TANK
Process tank, slight surface movement, rapid rate of change in level
It is possible, for instance, that the measured value will change in small steps rather than linearly
or will "freeze" at times when the setting is grossly incorrect.
8.6.17 Switching output
The functions for the switching output can be applied to:
a) the additional switching output in the Version "Ex-e or Ex-i current output HART
®
", or
b) the current output if Fct. 3.3.1 FUNCTION I is set to "SW.OUTP.".
time
too low
correct
too high
EPSILON R
example of a tank filling
level