Siemens Sitrans 사용자 설명서
7ML19985GE01
SITRANS LC 500 – INSTRUCTION MANUAL
Page 11
mm
mmm
mmm
Oper
at
ion & Applicat
ion
The measurement is further protected from interference by a buffer, which applies the
frequency signal from the measurement section to the active shield section. This effectively
eliminates any electrical potential difference between the shield and the measurement
section and prevents additional changes in capacitance occurring.
frequency signal from the measurement section to the active shield section. This effectively
eliminates any electrical potential difference between the shield and the measurement
section and prevents additional changes in capacitance occurring.
The relative lengths of the measurement section and active shield section can be
specified to suit a particular application. If the measured range will be short relative to
the total length of the electrode, specify a short measurement section. This increases the
achievable resolution of the measurement, since any change in level will be greater
relative to the length of the measurement section.
specified to suit a particular application. If the measured range will be short relative to
the total length of the electrode, specify a short measurement section. This increases the
achievable resolution of the measurement, since any change in level will be greater
relative to the length of the measurement section.
Measuring-
Circuit
Measuring-
Circuit
Conventional Capacitance
Measurement
SITRANS LC 500
with Active Shield
C1
C2
C3
R = (C1 + C2 + C3) + Ca
(C1 + C2 + C3) + Ca + Cm
R = Ca
Ca + Cm
Ca
Ca
Cm
Cm
R = Ratio between initial
capacitance and total
capacitance
capacitance
Ca = Initial capacitance (air)
Cm = Capacitance Increase
(product)
C1 =
Capacitance
connection
point
C2 = Capacitance connection
cable
C3 = Capacitance
Process
connection (includes active
part)
part)
frequency (f)
≈
K
capacitance (C)
active shield
active
measurement
section
measurement
section
probe seal
(inactive)
(inactive)
100%
0%
SITRANS
LC 500
LC 500
buffer
empty
tank
full
tank