Smart Transmitter

A process transmitter is a device that senses a physical parameter, whether that be pressure or temperature in an application and generates an output signal proportional to the measured input.

What is a ‘Smart’ Transmitter?

In order for an instrument to be coined ‘Smart’, it usually utilises a microprocessor. A microprocessor-based smart transmitter has a memory that can perform calculations, produce diagnostics and out-perform older, more conventional transmitters, when it comes to accuracy and stability.

Smart transducer is an analog or digital transducer or actuator combined with a processing unit and a communication interface. As sensors and actuators become more complex they provide support for various modes of operation and interfacing. Some applications require additionally fault-tolerance and distributed computing. Such high-level functionality can be achieved by adding an embedded microcontroller to the classical sensor/actuator, which increases the ability to cope with complexity at a fair price.

A ‘Smart’ Transmitter would also have a digital communication protocol that can be used for reading the transmitter’s measurement values and for configuring various settings in the transmitter. For engineer’s who need to configure and calibrate the transmitter, the digital communication protocol makes the biggest difference. Engineers can no longer simply measure the output analogue signal – they need to be able to communicate with the transmitter and read the digital signal.

Digital communication with Smart Transmitters

The most common digital communication protocols is HART protocol, which stands for Highway Addressable Remote Transducer. A HART transmitter contains both a conventional analogue mA signal and a digital signal superimposed on top of the analogue signal. Since it also has the analogue signal, it is compatible with conventional installations. Field bus and Profibus contain only a digital output, with no analogue signal.

FOUNDATION Fieldbus is an all-digital, serial, two-way communications system that serves as the base-level network in a plant or factory automation environment. It is an open architecture, developed and administered by the Fieldbus Foundation. It is targeted for applications using basic and advanced regulatory control, and for much of the discrete control associated with those functions. Foundation fieldbus technology is mostly used in process industries, but has recently been implemented in powerplants. FOUNDATION fieldbus was originally intended as a replacement for the 4-20 mA standard, and today it coexists alongside other technologies such as Modbus, Profibus, and Industrial Ethernet.

FOUNDATION fieldbus today enjoys a growing installed base in many heavy process applications such as refining, petrochemicals, power generation, and even food and beverage, pharmaceuticals, and nuclear applications. FOUNDATION fieldbus was developed over a period of many years by the International Society of Automation, or ISA, as SP50. In 1996 the first H1 (31.25 kbit/s) specifications were released. In 1999 the first HSE (High Speed Ethernet) specifications were released. The International Electrotechnical Commission (IEC) standard on field bus, including FOUNDATION Fieldbus, is IEC 61158.