Field instrumentation has played a key role in enabling these industries to meet those demands. It has evolved from relatively crude, pneumatic, mechanical devices to sophisticated microprocessor-based electronic transmitters. Pressure transmitters can now not only provide simple process variable (PV) information, but can also provide information about the health of the instrument and of the process itself.
Pressure measurement is one of the most commonly utilized measurements in a process manufacturing facility. Pressure can be used to infer flow in a pipe, level in a tank or pressure across a filter. Early pressure measurements relied on pneumatic devices, which were mechanical in nature, resulting in low reliability and high maintenance costs. During the late 1960s, the first step change in technology occurred with the development of electronic analog transmitters. These transmitters typically used capacitance measurement technology and resulted in more accurate and reliable measurement.
The advancement of sensor technologies and microprocessor-based electronics in the late 1980s provided significant improvement in pressure transmitter performance and reliability. Microprocessor advancements also led to the introduction of “smart” transmitters. Smart transmitters store additional information such as tag number, alarm information, product information and process data to allow for easier calibration and maintenance.
The multivariable transmitter incorporated measurement of differential pressure, pressure and temperature in a single device providing extremely accurate and reliable flow measurements. In addition, these sensor technologies provided for more efficient installations, in which the primary elements and isolation valves could be integrated into a single measurement solution that included the transmitter. This not only saved money but also helped minimize environmental impact.
Another significant development in the 1990s was the introduction of high-speed digital bus communication protocols. These protocols allowed significant installation savings due to reduced wiring costs, and also allowed the transmitter to transition from a simple PV provider to an information server. Because information is communicated continuously, control algorithms, such as proportional-integral-derivative (PID) and arithmetic blocks, as well as other basic control functions can be executed within the transmitter itself.
All of these advances have combined to produce notable advances in field instrumentation technology. For example, one recently released instrumentation series leverages advances in sensor and application-specific integrated circuit (ASIC) technology in order to double performance and reliability over previous models. It has introduced the concept of scalability, to allow the customer not only to choose level of performance, but also be able to provide an appropriate integrated pressure, flow or level solution. In addition, the platform is scalable from a technology standpoint to allow the integration of simple “featureboards” for implementation of advanced diagnostics capabilities as they are introduced.
Field instrumentation will play an increasingly important role in the process industry as more emphasis is focused on plant efficiency and predictive maintenance. Thus, the role of field instrumentation will continue to evolve with advances in sensor, microprocessor and communication technologies. While performance and reliability will continue to improve, the ability of the instrumentation to look into the process and detect subtle changes in process parameters will enable predictive information about the health of the instrument, process and associated equipment. The challenge will be to ensure that customers can easily implement this capability so that they may take full advantage of these benefits.
Scott A. Eliason, [email protected]
Scott Eliason is a product marketing manager at Rosemount Inc.
