Development Trends of Pressure and Differential Pressure Transmitters

Pressure and differential pressure transmitters are the most important category of process variable transmitters. They have a wide range of applications. They can be used for pressure, differential pressure, and other parameters such as flow, level, and specific gravity. For a 5000t/d cement production line, pressure transmitters must be installed at key parts of the process, such as the kiln head, the kiln tail, the top and bottom of the preheaters at all levels, the various air ducts and the cooling chambers, etc. To monitor the normal operation of the process. According to statistics, a total of 80 pressure transmitters are required for a new dry process cement production line.

The pressure transmitter is divided according to the measurement mechanism, the most common being capacitive, inductive, diffusion silicon, vibrating wire and so on. In recent years, ABB, YOKOGAVA and other companies have introduced new transmitters that use single-crystal silicon resonant and composite solid-state silicon as their measuring mechanisms. Their performance is further improved in various aspects; they are divided into analog and intelligent types by structural transmitters. And digital smart three generations of products. In the 80s of last century, China's self-constructed cement plants mostly used the Rosemount 1151 series transmitters introduced by Xi'an Instrument Factory, except that the accuracy of the DR differential pressure transmitter used to measure the negative pressure of the kiln head was 0.5. In addition to %, the rest is mostly 0.25%. It is characterized by the use of analog instruments with 4mA to 20mA transmission. The on-site display meter is an indicator with a range ratio of around 6:1 and a stability of 6 months. This is the first Generation analog transmitter.

The second generation of products is smart transmitters. The so-called smart concept is that sensors and transmitters are microprocessor-driven and have the ability to communicate and self-diagnose. In the United States, Honeywell introduced the smart transmitter ST3000 in 1983, and in 1989, it launched an all-digital two-way protocol smart transmitter. Many companies including Rosemount later also launched smart transmitters. In addition to the high precision (0.1% to 0.075%), high ratio (up to 100:1) and high stability (1 to 5 years), the smart pressure transmitter generally has the HART protocol or the company. The agreements, such as ABB's BaileyFSK, Yokogawa's BRAIN protocol, and later products also come with FF or PROFIBUS-PA protocol that conforms to the international standards of the fieldbus. It changes the local display meter to digital, and can also be operated by hand or under control. The remote configuration of the system enables remote setting or remote modification of the transmitter configuration data. In recent years, our new dry cement plant has almost all adopted smart pressure transmitters. The main products are: EJA series transmitters produced by Chongqing Yokogawa Instruments, CerabarS transmitters from EH, MV2000T from ABB, Siemens SITRANSP and Rosemount upgraded the 1151 and 3051C transmitters, many of which also chose smart pressure transmitters with FF or PROFIBUS-PA protocols.

Into the 21st century, the third generation of transmitters - digital intelligent transmitters gradually entered our field of vision, and its representative products are Rosemount's 3051S transmitter, ABB's 2600T265 series transmitters, Yokogawa's EJX transmitter and so on. The third-generation transmitter adopts advanced detection technology to eliminate the effects of humidity, dust, and other harsh environments on the transmitter. The accuracy is higher, and its accuracy is reported to be better than 0.05%. The sub-range of the range is finer, the range ratio is expanded to 200î—²1, the stability is more than 5 years, and the communication protocol is more complete. The new transmitter also passed the safety argumentation and can guarantee safe shutdown when the process condition exceeds the critical value. Since the second-generation transmitter can meet the cement plant monitoring requirements, and the third-generation transmitter price is still relatively high, the author believes that the cement plant should not be promoted temporarily.