Transmitters are essential components in the process industry. And change is inevitable in the industrial sector as of all other fields, many of the conventional instruments were replaced with smart instruments. Smart instruments are much-sophisticated equipment with digital displays and provide much more to access to control the equipment.
Still, for some applications, conventional transmitters are used especially at few hazardous locations. Here we up to discuss the main difference between the smart transmitter and Conventional transmitter.
The loop current is controlled by a traditional 4-20 mA transmitter and only provides a system variable signal.
The adjustments to zero and length were analog changes. The zero and span changes were limited to around 2-3 percent of the fixed zero and span values in the case of fixed range transmitters.
Some conventional transmitters have an adjustable turndown range, but a simulated process variable (applied calibration pressure or simulated temperature (RTD or thermocouple) is required to calibrate a turndown range.
A smart transmitter also does the same function as a conventional transmitter. In addition that they provides a better display of parameters need to show, eg: zero and span info, tag (instrument loop identification), diagnostics, or even multiple process variables using a digital protocol.
Configuration change can be done directly through the smart transmitter using the keypad or touch screen provided or through HART protocol.
With a handheld communicator or a modem and program, HART communication is done. Turndown rangeability can be as high as 100:1 (with decreased low-end accuracy); 15:1 or 20:1 with specified accuracy and can be achieved without an external calibration signal, reference or supply being applied.
Advantages of smart transmitter:
- Long term stability
- High accuarcy
- Allowing remote recalibration or re-alignment by sending them a digital signal
- Capacity to store the last calibration date and indicate when it will require the next calibration.
- Capacity to store data in order to assess the output of the plant and instrument