The development of pressure transmitters has gone through four stages:
(1) Early pressure transmitters adopted the working principle of large displacement, such as mercury float differential pressure gauges, diaphragm differential pressure transmitters, etc., with low accuracy and bulky.
(2) In the 1950s, there was a force balance differential pressure transmitter with high accuracy, but the feedback force was small, the structure was complex, and the reliability, stability and vibration resistance were poor.
(3) In the mid-1970s, with the emergence of new processes, new materials, and new technologies, especially the rapid development of electronic technology, displacement transmitters with small size and simple structure appeared.
(4) With the rapid development of science and technology in the 1990s, the measurement accuracy of transmitters has been improved, and they have gradually developed towards intelligence. Digital signal transmission is more conducive to data collection. Different types of transmitters have emerged, such as diffused silicon piezoresistive transmitters, capacitive transmitters, differential induction transmitters, and ceramic capacitive transmitters.
As a precision instrument, transmitters play an important role in the petroleum and petrochemical industry. The transmitter can not only convert some commonly used quantities into the expected required quantities, but also amplify some commonly used quantities. In various fields and industries, transmitters can be divided into pressure transmitters, integrated temperature transmitters, liquid level transmitters, etc. In the petroleum and petrochemical industry, pressure transmitters are often the most widely used and widely applied reasons. This article also takes pressure transmitters as the main research instrument calibration object. For the above-mentioned other functional transmitters, they will be explained in the attached table below, and their respective characteristics will be analyzed.
The main work of the pressure transmitter is to transmit the pressure signal commonly used in the petroleum and petrochemical industry to the electronic equipment, and reflect it in the computer operation through AD conversion. For example, taking water pressure as an example, the pressure signal generated by water pressure is transmitted to the heart device to generate the corresponding current (most transmitters currently have a current of 4-20mA). According to the corresponding algorithm formula, the current converted by the pressure transmitter also increases with the increase of the pressure signal generated by the pressure.
From a macroscopic point of view, the pressure transmitter uses the pressure star sensor to realize the size of the pressure, and then realizes AD conversion through the module circuit to obtain the voltage or current within the available range. Microscopically, the pressure is reflected in the integrated silicon pressure elements, forcing them to be deformed by the pressure, causing the bridge to act to obtain the corresponding voltage and current, and then the amplifier circuit amplifies the voltage and current obtained in the early stage and converts them into usable voltage or current.
According to the angle of measurement using the pressure transmitter. It can be divided into pressure transmitter and differential pressure transmitter. As the name implies, the former is a measurement of pressure, and the latter is a measurement of pressure difference. But the pressure transmitter well in principle can not only use this function, but also involve other indirect measurement quantities. For example, the upper and lower limits can be measured separately with two pressure transmitters or one differential pressure transmitter, and the difference of the electrical signal can be obtained, which can reflect the height of the liquid level. You can also measure the flow and density of the measured medium by intercepting the assembly, which shows the powerful function and wide application range of the pressure transmitter.
Pressure sensors can be classified not only from the perspective of satellite use, but also according to the structural scale of the pressure transmitter. Since the pressure transmitter is in direct contact with the measured liquid medium, considering that it is used in the petroleum and petrochemical industry, the liquid is often corrosive, causing damage to precision instruments and subsequent maintenance work. For this reason, pressure transmitters are divided into ordinary type and isolated type. The general pressure transmitter contacts the measured medium through the inner membrane in the black box of the zero protection transmitter, while the isolated pressure transmitter is sealed with silicone oil, which exists in the bellows as a protective liquid, and the outer membrane of the pressure transmitter contacts the measured medium. When the measured medium is pressed on the outer membrane, the silicone oil protective liquid in the inner membrane transmits the pressure to the ordinary bellows. On the other hand, compared with the general pressure transmitter, the isolated pressure transmitter has the advantage of not blocking the bellows chamber of the pressure conduit. Since the measured medium often carries dirty oil, it often blocks the bellows, and even due to the separation of the medium and the transmitter, crystallization will occur, forcing the medium to be pumped out of the pressure transmitter, which will definitely cause the pressure transmitter to not work properly, or even paralyze on a large scale, delaying the construction period. Usually, the isolated pressure transmitter adopts a flange connection method to allow the sensing diaphragm of the isolated pressure transmitter to enter the measured device, effectively solving the problems of blockage and stuck drill. Therefore, the measured medium will not be extracted by the wave.
