Process Variable Transmitter Technology Trends

First, what is a process variable transmitter (PVT)

In order to achieve cement process control, process automation variables must be collected from the site. Process variables are mainly concentrated in four major categories, namely, pressure, temperature, material level, and flow rate. The so-called process variable transmitter converts changes in the physical quantity sensed by the sensor into an accurate, standard analog or digital signal and sends it to the network. Realize the connection of process sensors and control systems in the field. The process variable transmitter is at the bottom of the pyramid model of the control system, but it is a very critical link. A typical 5000t/d cement production line needs to detect about 500 to 600 process variables, and the point to be alarmed is about 1000. One. According to the statistics of a 2500t/d production line of the China Cement Group, there are 495 process variables to be monitored by the computer system, and the number of alarm points required is about 720. Therefore, a 2500t/d cement production line is required for the process variable transmitter. About 500 or so. Based on the fact that process variable transmitters have a wide range of applications, many are required and process monitoring is indispensable, major cement groups attach great importance to the selection of process variable transmitters. In the past two decades, the sensor and transmitter technologies have made great progress, such as increased sensitivity, reduced response time, reduced hysteresis, and long-term stability and durability. These characteristics make the process changeable. The feeder becomes more accurate, more reliable, more stable, and more secure. With continuous improvement of new dry process cement technology and rapid advancements in electronic technology, process variable transmitters have also gone through three generations of analog, intelligent and digital intelligence. Process variable transmitters installed in China's cement production lines are also simulated. Go to smart and start using a transmitter with fieldbus FF or PROFIBUS-PA protocol.

Second, pressure transmitter technology development pressure, differential pressure transmitter is the most important category of process variable transmitter, a wide range of applications, in addition to pressure, differential pressure measurement can also be used for flow, Level, specific gravity and other parameters are measured. 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, and Siemens. Many of the SITRANSP and Rosemount upgraded 1151 and 3051C transmitters also use 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 uses 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—¾1, 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.

Third, the technological development temperature of the intelligent temperature transmitter is also a very important category in the process variable transmitter. It is one of the basic elements for measuring flow, density and other process variables. A 5000t/d cement production line must have temperature transmitters installed in key parts of the process and important equipment. According to statistics, a new dry process cement line requires a total of 80 to 100 pressure transmitters.

Based on the great progress in the development of temperature measurement, it also promotes the accuracy, reliability and repeatability of temperature transmitters in the field of process control industry, and at the same time, it also contributes to the continuous improvement of process control quality. contribution.

The so-called smart temperature transmitter refers to a temperature transmitter that combines the temperature sensor technology with additional electronic components. It can realize remote setting or remote modification of configuration data. Looking at the current temperature transmitter market and the application of the cement industry, there are mainly three types of different intelligent temperature transmitter products. From the application and cost perspective, each type of smart temperature transmitter has its advantages and disadvantages.

1. Weatherproof Temperature Transmitters These types of temperature transmitters are often installed in demanding, demanding applications such as kiln tails, precalciners, and five-stage preheaters. This type of temperature transmitter is housed in a hermetically sealed housing, which is usually made of stainless steel. Its characteristics are high accuracy, high reliability, good safety, and weatherproof. Its main disadvantage is its relatively low price. high. It usually has an on-site header that can be monitored, adjusted and configured on site. Representative products are EMERSON's 3144, 3244 and Beijing Far East's 444. In addition, EH and Siemens also have similar products.

2. DIN rail mount, instrument panel mounted temperature transmitters These types of temperature transmitters can be DIN rail mounted and are usually installed in the control room. It is cheap, simple to install and maintain, and can match different types of temperature sensors by changing the configuration. The measurement accuracy is lower due to the longer connection wire with the remotely mounted sensor. This type of temperature transmitter can be recommended for cement mills.

3. Integrated Temperature Transmitter This type of temperature transmitter can be mounted directly on the DIN connector of the temperature sensor. It has the advantages of low installation cost, compact size, and compatibility with various types of temperature sensors. Since this temperature transmitter is directly mounted on the temperature sensor's connector, the electrical connection and sensor wiring are very simple. Cement plant kiln system in addition to the requirements of the site, the use of integrated temperature transmitter, grinding system can also be used.

The communication protocol used by the smart temperature transmitter is the same as that of the pressure transmitter. The HART protocol is the dominant one, and the FF or PROFIBUS-PA protocol conforms to the international standards of the field bus.

IV. Technological development of process variable transmitters The main trends of current process variable transmitters are wireless applications, smaller form factors and the application of multivariable process transmitters. As some cement large groups have adopted wireless technologies for their local auxiliary processes, for example, Jidong Cement Group has adopted wireless control at circulating pump stations, and some cement plants in Zhejiang use wireless control to load and unload bulk cement vessels. Wireless transmitters will also receive Cement industry concerns. It is worthwhile to add the wireless function to the process variable transmitter. Considering that some cement plants occupy a large amount of physical space, some process measurement locations are difficult to install, and some process measurement point environments are very harsh and use traditional hard links. The cost of wire-mounting devices is too high. If the connection between the process variable transmitter and the control circuit is eliminated, switching to wireless communication can save energy and reduce the wiring and maintenance costs, so the wireless function is added to the process variable transmitter. Value for money, wireless communication technology is another hot technology after the field bus and industrial Ethernet. Wireless variable transmitters Typical products and applications are the XYR5000 series of wireless pressure transmitters based on the Zig-Bee wireless transmission protocol introduced by Honeywell in the United States in 2004. They can monitor pressure, differential pressure, time, and ultrasonic noise. They are used to Add the wireless function to the analog input interface on the 4mA to 20mA device and the optional external antenna. Its accuracy is ±0.1% and the battery life is 5 years.

In the new dry cement production line, the process variable transmitter is very important as a monitor eye. It improves the accuracy, reliability, stability, and safety, and makes continuous improvement for the process control quality and the final product quality. Contributed.