Rosemount 3152 - Transmitter Theory of Operation

Reference Manual
00809-0100-4835 Rev BD
July 2016
Rosemount 3150 Series
4-2
TRANSMITTER THEORY OF
OPERATION
The block diagram in Figure 4-1 illustrates the operation of the 3150
series pressure transmitter.
The 3150 series pressure transmitters have a variable capacitance
sensor (see Figure 4-2). Differential capacitance between the sensing
diaphragm and the capacitor plates is converted electronically to a 2
wire, 4-20mA dc signal based on the following formulas:








+
−
=
21
12
1
CC
CC
kP
Where:
P is the process pressure.
k
1
is a constant.
C
1
is the capacitance between the high-pressure
side and the sensing diaphragm.
C
2
is the capacitance between the low-pressure
side and the sensing diaphragm
2
1
CC
I
fV
ref
p
p
+
=
−
Where:
I
ref
is the reference current.
V
p-p
is the peak to peak oscillation voltage.
f is the oscillation frequency.
( )
1
2
CCfVI
ppdiff
−=
−
Where:
I
diff
is the difference in current between C
1
and C
2
.
Therefore:
P = constant x I
diff
= I
ref
12
12
CC
CC
+
−