Transmitter Theory Of Operation - Emerson Rosemount 2151N Reference Manual

Reference Manual
00809-0000-4851 Rev AD
December 2023
TRANSMITTER THEORY OF
OPERATION
Operation
The block diagram in Figure 4-1 illustrates the operation of
the 2151N pressure transmitter.
The 2151N pressure transmitter has 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, 4-20 mA dc signal based on the
following formulas:
���� = ����
Where:
P is the process pressure.
k is a constant.
1
C is the capacitance between the high-pressure
1
side and the sensing diaphragm.
C is the capacitance between the low-pressure
2
side and the sensing diaphragm.
Where:
I is the reference current.
ref
V is the peak to peak oscillation voltage.
p-p
f is the oscillation frequency.
����
�������� ���� ����
Where:
I is the difference in current between C
diff
C .
2
Therefore:
���� = �������������������������������� ���� ����
Rosemount 2151N
���� − ����
� �
2 1
���� + ����
1
1 2
����
�������� =
������������
���� + ����
����−����
1 2
= �������� ( ���� − ���� )
����−���� 2 1
���� − ����
= ���� �
2
���� + ����
�������� ���� ���� ������������
2
and
1
�
1
1
42