Smart transmitters

Fig. 16. Exploded view of a smart transmitter based on variable capacitance sensor technology.

Microprocessor-Based Transmitters The cost of microprocessor technology has declined to the point where it is economic ly feasible to incorporate a microprocessor into each transmitter. Such microprocessor-based transmitters are often referred to as smart transmitters. As opposed to conventional or dumb transmitters, the smart transmitters offer the following capabilities ... 

Compensation of the measured value for conditions within the instrument, such as compensating the output of a pressure transmitter for the temperature within the transmitter. Smart transmitters are much less affected by temperature and pressure variations than conventional transmitters. 

Due to these capabihties, smart transmitters offer improved performance over conventional transmitters. 

Transmitter/Actuator Networks With the advent of smart transmitters and smart actuators, the limitations of the 4-20 milliamp analog signal transmission retard the full utilization of the capabilities of the smart devices. For smart transmitters, the following capabilities are required ... 

Transmission of more than one value from a transmitter. Information beyond the measured variable is available from the smart transmitter. For example, a smart pressure transmitter can also report the temperature within its housing. Knowing that this temperature is above normal values permits corrective action to be taken before the device fails. Such information is especially important during the initial commissioning of a plant. 

Bidirectional transmission. Configuration parameters such as span, engineering units, resolution, and so on, must be communicated to the smart transmitter. 

In order to meet their initial requirements, several manufacturers have developed digital communications capabilities for communicating with smart transmitters. These can be used either in addition to or in lieu of the 4-20 milliamp signal. Although most manufacturers release enough information on their communications features to permit another manufacturer to provide compatible instruments (and in some cases provide an open communication standard), the communications cap ihty provided by a manufacturer may be proprietaiy. 

Multivariable smart transmitters, 20 664 Multivariate Adaptive Regression Splines (MARS), 6 53... 

Henkel, S. Single Optical Fiber Does It All for Smart Transmitters. Sensors 8 (January 1992). 

Smart Transmitters and Associated Protocols—Intelligent Hardware... 

An instrument which not only measures a variable, but also carries out further processing in order to refine the data obtained before presentation either to an observer or to some other stage of the system, is generally termed intelligent or smart. In practice, additional functions are usually available as well as the data-processing facility and these are all normally contained within the transmitter of the measuring device. These so-called smart transmitters are microprocessor-based and enable the device ... 

The cost of an intelligent instrument can be twice that of the equivalent device without the smart facility (the latter is termed a dumb instrument)(99). However, the use of a smart transmitter does generally improve the inherent accuracy of the sensor itself. 

A common feature of smart devices is the ability, either to transmit the normal 4-20 mA analogue output (which is digitally linearised and compensated where necessary), or to provide digital communication with other devices as desired. Digital communication with a smart transmitter can be implemented from a microprocessor within the control room, or by the use of a hand-held terminal. The latter can be inserted at any point within the 4-20 mA current loop and instructions to change the range, calibration, etc. can be sent to a specific smart device(l00>. 

Eventually this technology, generally referred to as field bus, will replace all other forms of transmission (analog, pulse, and serial). Its acceptance by the user community has been slow, mainly due to the absense of a standard. Smart transmitters and smart valves have gained widespread acceptance, but initially the signal transmission continued to be via current loops. During tfiis interim, several manu-... 

Measurement Devices and Final Control Elements This lowest layer couples the control and information systems to the process. The measurement devices provide information on the current conditions within the process. The final control elements permit control decisions to be imposed on the process. Although traditionally analog, smart transmitters and smart valves based on microprocessor technology are now beginning to dominate this layer. 

Smart" field communicator for remote calibration and configuring of "smart" transmitter 1,000-3,000... 

TC Wire Errors For Wires Transmitter Error Is Additional and Recommended Span of Different Qualities3 in the Case of "Smart" Transmitters Limits3... 

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