What is a Smart Pressure Transmitter?

Figure 1: A sample of a Trumen TFP-40S smart pressure transmitter.

The definition of a smart pressure transmitter is arguable. Some people think that smart pressure transmitters refer to those with highway addressable remote transducer (HART) protocol output; others think that pressure transmitters with adjustable pressure measurement range can be regarded as smart pressure transmitters. Generally speaking, a smart pressure transmitter is a pressure uses a microprocessor to process the collected signals, which makes it possible to achieve some functions that simple circuits cannot achieve through logical operations.

The smart pressure transmitter consists of two parts: smart sensor and smart electronic board. The smart sensor part includes: capacitive sensor, measuring diaphragm, temperature sensor and temperature compensation circuit. The smart electronic board part includes: microcomputer controller and peripheral circuit, responsible for completing the conversion of pressure signal to 4 ~ 20mA DC.

The Differences between a Smart Pressure Transmitter and an Ordinary Pressure Transmitter

Their differences mainly lie in signal conversion: the pressure transmitter converts other signals into analog signals and outputs them to the device. The signal format of the smart pressure transmitter is compatible with analog and digital. And the analog signal and the digital signal share a channel, and use the protocol (HART) to communicate. In simple terms, it can monitor the scene or connect with the host computer to form an on-site monitoring system through the chip in the smart pressure transmitter.

In addition, in terms of use, the smart pressure transmitter can obtain the information of the field equipment without being on-site, and can directly save the allocation information of the field pressure transmitter to the remote computer through transmission. Ordinary pressure transmitters do not have such a function.

The Constitution of Smart Pressure Transmitters

Figure 2: Smart pressure transmitter’s components and working principles in block diagram.

Smart pressure transmitters are generally composed of sensors, microprocessors, memory and analog-to-digital and digital-to-analog converters.
Sensors are used to detect the signal being measured, and the materials used vary from manufacturer to manufacturer. Yokogawa EJA uses a silicon resonance type, which converts the measured parameters into the vibration frequency of the silicon beam; Fuji's FCX-A/C is a silicon micro-capacitor type, and the measured differential pressure or pressure value is obtained by measuring the capacitance.
The microprocessor is the core of the smart transmitter and is responsible for the comprehensive operation and processing of the data, such as linearization of the detection signal, range readjustment, function operation, working unit conversion and diagnosis and communication functions.
The memory is used to store various constants, programs, and transmitter configurations that are called by the microprocessor, and are generally rewritable.
Analog-to-digital and digital-to-analog converters convert analog signals to digital signals. An analog-to-digital converter is required for the detection signal of the sensor to the microprocessor, and a digital-to-analog converter is required to output the 4-20mA signal from the microprocessor.
The smart transmitter needs to output a digital signal to communicate with the distributed control system (DCS), and a smart field communicator (SFC) or a hand-held communicator is attached to communicate with the transmitter. In addition, the smart transmitter is equipped with a backup power supply to avoid data loss in the memory during a power failure.

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