Basics of smart transmitters

instrumentation

#1

What is a Smart transmitter?

Smart transmitters are microprocessor-based transmitters that can perform calculations, produce diagnostics. They are useful in remote area communication and calibration process. The sensor signal transmitter into a unified standard signal: 0/4-20mADC, 1-5VDC, 0-10VDc. The output control signal is standard such as 4-20mA.

A smart sensor is insensitive to noise and which use the digital communication protocol that can be used for reading transmitter measurement and configure various settings in the transmitter.

Block Diagram:

smart transmitter

A smart transmitter is a microprocessor-based transmitter which includes a signal processing system.

The smart transmitter has one extra inbuilt sensor, the purpose of this sensor is to measure the atmospheric parameter which gives the compensate for, environmental disturbances

There is two output provided, the 4-20mA analog signal and digital value through HART modem. HART signal is used during calibration. The communication standard used by smart transmitters is the Hart protocol, which employs frequency shift keying (FSK).

The microprocessor/microcontroller is available with memory where we can write our settings in. Long range communication is possible with 4-20mA signal, thus twisted pair wire is used.

Other main features:

  • Often incorporate multiple sensors covering different measurement ranges and allow automatic selection of the required range. The range can be readily altered if initially estimated incorrectly.

  • Can adjust for non-linearities to produce a linear output

  • Self-calibration: Capability that allows removal of zero drift and sensitivity drift errors.

  • Self-diagnosis and fault detection: Self-diagnostic capability that allows them to report problems or requirements for maintenance. The best theoretical approach to this difficulty is to apply mathematical modelling techniques to the sensor and plant in which it is working, with the aim of detecting inconsistencies in data from the sensor. It is not used widely as it is a little expensive.

Advantages:

  • Improved accuracy and repeatability

  • Long-term stability is improved and required recalibration frequency is reduced

  • Reduced maintenance cost

  • Single penetration into the measured process rather than the multiple penetration required by discrete devices, making installation easier and cheaper

  • Allowing remote recalibration or re-ranging by sending a digital signal to them

  • Reduction in number of spare instruments required, since one spare transmitter can be configured to cover any range and so replace any faulty transmitter.

  • Ability to store last calibration date and indicate when next calibration is required.

  • Long-term stability is improved and required recalibration frequency is reduced

  • Ability to store data so that plant and instrument performance can be analysed