What is a Pressure Transmitter?

Figure 1: Different types of pressure transmitters.

A pressure transmitter is a device that converts pressure into pneumatic or electric signals for control and remote transmission. It can convert physical pressure parameters such as gas and liquid sensed by the pressure transducer into standard electrical signals (such as 4~20mADC, etc.), which secondary instruments such as indicating alarms, recorders and regulators can use for measurement, indication and process regulation.

There are two types of pressure transmitters: electric and pneumatic. The electric unified output signal is DC signal such as 0~10mA, 4~20mA or 1~5V. The pneumatic unified output signal is a gas pressure of 20-100Pa. According to different conversion principles, it can be divided into force (torque) balance, capacitive, inductive, strain and frequency types.

Pressure transmitters are one of the most commonly used sensors in industrial practice. It is widely used in various industrial automation environments, such as water conservancy and hydropower, railway transportation, intelligent buildings, production automation, aerospace, military, petrochemical, oil wells, electric power, ships, machine tools, pipelines and many other industries.

The Characteristics of the Pressure Transmitter

1. Wide range of measurable media, including oil, water and paste compatible with 316 stainless steel and 304 stainless steel; with certain anti-corrosion ability;
2. High accuracy, high stability, good linearity and high temperature stability;
3. Small size, light weight, easy to install, debug and use;
4. Stainless steel fully enclosed shell, good waterproof;
5. Dedicated integrated circuit, few peripheral devices, high reliability and simple maintenance.

The Working Principles of the Pressure Transmitter

Figure 2: Sectional view of the components and structures of the pressure transmitter.

The main function of the pressure transmitter is to transmit the pressure signal to the electronic device, and then display the pressure in the computer. The principle is roughly as follows: the strain gauge is tightly bonded to the matrix that generates mechanical strain through a special adhesive. When the stress of the substrate changes, the resistance strain gauges also deform together, so that the resistance of the strain gauges changes, making the voltage applied to the resistance to change.
The pressure of the electronic signal output in this way has a linear relationship with the magnitude of the voltage or current, which is generally proportional. Therefore, the voltage or current output by the transmitter increases as the pressure increases.

The two pressures of the measured medium of the pressure transmitter pass into the high-pressure chamber and the low-pressure chamber. The pressure of the low-pressure chamber adopts atmospheric pressure or vacuum, which acts on the isolation diaphragms on both sides of the delta element (i.e., the sensitive element), and is transmitted to both sides of the measuring diaphragm through the isolation diaphragm and the filling liquid in the element. When the pressure on both sides is inconsistent, the measuring diaphragm is displaced, and its displacement is proportional to the pressure difference.

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