6
OPERATION
94
OPTIFLEX 1300 C
www.krohne.com
01/2008 • 4000172301 - HB OPTIFLEX 1300 R02 en
6.4.9 Thresholds and parasite signals
General notes
The low-power electromagnetic signal from the instrument goes down the probe. The surface of
the process and objects in the tank make reflections. These reflections go back up the probe to
the signal converter. The signal converter converts the reflections into voltage amplitudes.
Reflections from objects in the tanks show as interference signals (parasites).
How thresholds work
Thresholds let the instrument ignore reflections with small amplitudes and monitor changes in
level or interface. The voltage amplitude of signals depends on the distance of the reflection
from the signal converter. Because the voltage amplitude decreases as distance increases, the
threshold decreases logarithmically. The instrument uses largest signal that goes across the
threshold.
The instrument uses the menu items that follow:
•
Level threshold (C.1.16) to monitor the level signal
•
Level threshold (C.1.16) and interface theshold (C.1.17) to monitor level and interface signals
•
Probe end threshold (C.1.18) to monitor the probe end signal in TBF mode. If the instrument
operates in TBF mode or must calculate the
ε
r
of the product, there must be a good probe end
signal.
The electronics of the instrument amplify the signal. The amplification factor (level of Gain)
depends on the strength of the signal. There are 7 levels (1 to 7). A strong signal is given Gain 1,
while a weak signal is given Gain 7. When you fill or empty the tank, the instrument usually
identifies the signal. It automatically changes the Gain to monitor the position of the signal. But
the instrument cannot monitor the correct signal if:
•
There are too many objects in the tank.
•
There is an object that makes a large reflection in the tank.
NOTE!
Also refer to How to use the snapshot function to filter parasite signals that do not move
on
page 97 to use the snapshot function to filter parasite signals. For more data on menu items,
refer to
C. Advanced setup
on page 77.
HB_OPTIFLEX1300_EN_D4_080428.book Page 94 Tuesday, April 29, 2008 2:47 PM
