Section 2
2.1
OPERATION
The
LD303
Series Pressure Transmitters use capacitive sensors (capacitive cells) as pressure
sensing elements, as shown in Figure 2.1. This is exactly the same sensor as the LD301 series
uses, the sensor modules are therefore interchangeable.
Figure 2.1 - Capacitive Cell
Functional Description - Sensor
Where,
P
1
and P
2
are the pressures and P
1
≥
P
2
CH = Capacitance between the fixed plate on P
1
side and the sensing diaphragm.
CL = Capacitance between the fixed plate on the P
2
side and the sensing diaphragm.
d = Distance between CH and CL fixed plates.
∆
d = Sensing diaphragm's deflection due to the differential pressure
∆
P = P
1
- P
2
.
Knowing that the capacitance of a capacitor with flat, parallel plates may be expressed as a function
of plate area (A) and distance (d) between the plates:
d
A
C
×
≈
ε
Where,
ε
= Dielectric constant of the medium between the capacitor's plates.
CL
d
d
A
d
d
A
CH
≈
∆
−
×
∆
+
×
≈
)
2
(
and
)
2
(
ε
ε
However, should
CH
and
CL
be considered as capacitances of flat and parallel plates with identical
areas, then:
However, should the differential pressure (
∆
P) apply to the capacitive cell not deflect the sensing
diaphragm beyond d/4, it is possible to assume
∆
P as proportional to
∆
d, that is:
d
∆
∝
∆
P
By developing the expression (CL - CH)/(CL + CH), it follows that:
d
d
CH
CL
CH
CL
∆
=
+
−
2
Содержание LD303
Страница 1: ...Profibus PA Pressure Transmitter L D 3 0 3 M E...
Страница 8: ...LD303 Operation and Maintenance Instruction Manual VIII...
Страница 15: ...Installation 1 7 Figure 1 1 f Dimensional Drawing and Mounting Position Sanitary Transmitter with Extension...
Страница 22: ...LD303 Operation and Maintenance Instruction Manual 1 14...
Страница 26: ...LD303 Operation and Maintenance Instruction Manual 2 4...
Страница 49: ...Configuration 3 23 Figure 3 24 Block Mode for Totalizer Block Figure 3 25 Set Reset for Totalizer Block...
Страница 74: ...LD303 Operation and Maintenance Instruction Manual 4 6 Figure 4 4 Exploded View...
Страница 83: ...Maintenance Procedures 4 15 Figure 4 8 TPE Software Screen...
Страница 102: ...LD303 Certifications Information A 4 CSA NEMKO and EXAM CEPEL NEPSI...
Страница 104: ...LD303 Certifications Information A 6 CEPEL...
Страница 105: ...Appendix A A 7 Control Drawing Factory Mutual FM...
Страница 106: ...LD303 Certifications Information A 8...
Страница 108: ...LD303 Operation and Maintenance Instruction Manual B 2...