Principle and characteristics of capacitive pressure transmitter
Generally, the distance of transmitting pressure information with a pressure gauge cannot be very far. If you want to transmit pressure information long-distance, it is often a pressure transmitter that combines elastic side pressure elements and electrical sensors. It is often referred to as a differential pressure transmitter in the industry. It can transmit, display and control with a unified signal. Commonly used are capacitive pressure transmitters, inductive pressure transmitters, Hall pressure transmitters, etc.
1. Principle of capacitive pressure transmitter
1.1 The principle of the tomb
For capacitors composed of two parallel plates, edge effects are not considered. Its capacitance is
(3-55)
In the formula, C—the capacitance F of the parallel plates;
d—distance between parallel plates.m;
ε-dielectric constant between parallel plates, F/m;
S—plate area.m2
When any parameter of d, ε or S in the formula (3-55) changes due to the change of the measured value, the capacitance C also changes accordingly. Therefore, there are three basic types of capacitive sensors. That is, variable pole distance (d) type, variable area (S) type and variable dielectric constant (e) plastic. Variable-area and variable-pole-distance capacitive sensors generally use air as the dielectric. The dielectric constant of air is almost unchanged in a very wide frequency range, the temperature stability is good, the conductivity of the medium is extremely small, and the loss is extremely small. Their electrode shapes are flat, cylindrical and spherical.
2. Features of capacitive pressure transmitter
The measurement range of the capacitive pressure transmitter is -1 × 107 ~ 5 × 107 Pa. It can work at an ambient temperature of 46 ~ 100 °C
make. Its advantages are:
(1) The energy required for input is extremely low.
(2) The sensitivity is high, and the relative change of capacitance can be large.
(3) The structure can be made with high rigidity and low mass, so the natural frequency is high. Since there are no mechanical moving parts, the loss is small.
So it can work at very high frequency.
(4) Good stability. High accuracy of side measurement. Its accuracy can reach ±25%～±0.05%
(5) Simple structure, anti-vibration, durable. Can work in harsh environment.
