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Let’s talk about the history of pressure transmitters and the technical factors that drive the development of their third-generation versions. As is well known, pressure parameters are key indicators in process control, and pressure transmitters represent the most important and numerous type of automation devices among all the measuring instruments used in automation systems. Since Rosemount pioneered the era of micro-displacement transmitters in 1969, we have unknowingly embarked on a 50-year journey in the field of pressure transmitters. Today, the technical editor from Xi’an Hongli Yuanfan will talk to you about the history of pressure transmitters and the technological factors behind their third-generation products. I. Measurement of pressure parameters In the early days, in addition to local pressure gauges, there were two other types of devices used for measuring pressure parameters: base-type pressure instruments, and transmitter-type instruments that are part of unitized instrumentation systems. Base-type pressure instruments, such as those with mercury floats or double bellows, combine the measuring section, conversion section, indication and recording section, as well as any possible computing or regulating sections, all within the instrument’s housing; hence they are called base-type instruments. Mercury float-type instruments are devices that contain mercury; mercury is toxic and poses a serious threat to the health of those who use and maintain such instruments. In China, these instruments were phased out in the late 1960s, and double-diaphragm types were used instead for pressure measurement. However, due to issues such as the lack of remote transmission capability, large size, inability to adjust the measurement range, and low accuracy, their use has become increasingly rare. II. The Origin and Characteristics of Pressure Transmitters With the development of instrumentation technology, unitized combination instruments came into being. Each of the comprehensive functions of the aforementioned base-type instruments was assigned to a specific type of instrument: the detection function was handled by transmitters, the display function by indicators, the recording function by recorders, the calculation function by calculators, and the control function by controllers. Standardized unified signals such as 4mA–20mA and 0–10mA were used for communication between these different types of instruments. Thus, the transmitter as we know it was created. It is defined as a device or apparatus that can detect a specified physical quantity to be measured and convert it into a specified standard signal according to certain rules. A transmitter typically consists of a sensitive element and a signal converter. For transmitters that measure pressure and differential pressure signals, the physical quantities being measured include pressure, differential pressure, absolute pressure, negative pressure, liquid level, density, and so on. In the 1960s and 1970s, electric and pneumatic combined instruments were widely used in China; the pressure measuring transmitters used at that time were force-balanced and vector-type transmitters, with an accuracy of around 1%. In the 1960s, force-balance pneumatic transmitters were widely used in the U.S. instrumentation market, but they had drawbacks such as tendency to drift, a large number of moving parts, and high maintenance requirements. In 1969, Rosemount converted its first patented invention – a variable-capacitance pressure sensor – into the 1151 capacitive pressure transmitter, using electrical signals in place of pneumatic signals. In pressure measurement, capacitive transmitters exhibit minimal displacement and deformation of their sensing elements, which marked the beginning of a new era for micro-displacement transmitters; they have made significant progress in terms of stability, reliability, and accuracy. Since then, various instrument manufacturers have introduced their own micro-displacement pressure transmitters, with principles of operation such as inductive, diffused silicon, string vibration, resonant, and ceramic types. III. Representative models of third-generation products from various manufacturers Starting with the introduction of the 1151 analog pressure transmitter in 1969, Rosemount has developed three generations of transmitter products: the 1151 analog capacitive pressure transmitter represents the first generation; the 3051 intelligent transmitter introduced in 1988 constitutes the second generation; and the 3051S digital intelligent transmitter released in 2001 represents the third generation. To date, over 15 million Rosemount pressure transmitters have been used by more than 85,000 customers in 75 countries around the world. Internationally, the FC series transmitters from Fuji in Japan, as well as the EDR/EPR series transmitters from Hitachi in Japan, also belong to the first generation of analog products ； The ST3000 transmitters from Honeywell in the United States, the EJA transmitters from Yokogawa in Japan, the Cerabar S transmitters from E+H in Germany, the I/A transmitters from Foxboro in the United States, the FCX transmitters from Fuji in Japan, the XTC transmitters from Moore in the United States, the LD301 and LD302 transmitters from Smar in the United States, as well as the SITRANS P DSIII transmitters from Siemens in Germany and the MV2000T transmitters from ABB in Germany are intelligent second-generation products ； The EJX transmitters from Yokogawa in Japan, the ST3000/100 transmitters from Honeywell in the United States, and the 2600T265 series of transmitters from ABB in Germany can be regarded as third-generation digital intelligent transmitters. Recommendations for brands and products related to imported pressure transmitters: 1. Rosemount transmitter 3051 product series; 2. Yokogawa EJA pressure transmitters – Series E from Japan; 3. Cerabar S transmitters produced by E+H in Germany; 4. SITRANS P DSIII transmitters from Siemens in Germany; 5. ST3000 transmitters from Honeywell in the United States