Smart transmitters

About SMART Transmitters

1. Smart Transmitters

2. Table of content What are SMART transmitters? Difference between Conventional Transmitters and Smart Transmitters What is the need of SMART transmitters? SMART transmitter and HART Transmitter – block diagram How HART transmitter works? HART Communication Protocol HART Networks Point-to point Multidrop. How are HART instruments calibrated? And is HART calibration required ? benefits of HART protocol Advanced HART Application Is calibration of Smart Transmitter important? How to calibrate a Smart transmitter? Advantages and disadvantages of smart transmitters references

3. What are Smart Transmitters ? A smart transmitter is a microprocessor-based transmitter that can be programmed, has a memory, can perform calculations, self-diagnostics, reports faults, and can be communicated with a remote location.

4. Conventional Transmitters Work on basic loop current and does not allow digital reading. Readings on conventional transmitters deflect by 2-3% of the fixed reading value. The range ability of the conventional transmitter is 5:1 Conventional transmitters are not accurate It is difficult to do communication and monitoring. Smart Transmitters The smart transmitters work on the Highway Address Remote Transducer (HART) protocol. Zero value in the reading increases the accuracy of smart transmitters. The smart transmitter offers over 100:1 Smart transmitters highly accurate without any calibration. Communication and monitoring, a smart transmitter makes both easier. V/S

5. What is the need of SMART Transmitter? 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. There are two types of communication protocols used in smart transmitter that makes communication easy: HART (Highway Addressable Remote Transmitter) SMART (Single Modular Auto-ranging Remote Transducer)

6. It is a communication protocol. 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. HART standard helps instruments to digitally communicate with one another over the same two wires used to convey a 4-20 mA analog instrument signal. HART (Highway Addressable Remote Transmitter) SMART transmitters compared to analog transmitters have microprocessor as their integral part , which helps for self diagnostic abilities , non-linear compensations , re-ranging without performing calibrations ,and ability to communicate digitally over the network. SMART (Single Modular Auto ranging Remote Transducer)

7. Smart Transmitter Block Diagram

8. SMART Transmitter consist of three basic parts The input portion contains the process sensor or transducer as well as the ADC Analog to Digital Converter. The involved process vector (e.g. friction, temperature, wind, etc.) is calculated by the sensor and then converted to a relative electrical signal. The measured electrical signal is then converted into a digital register by the Analog to Digital Converter (ADC).  This digital count, which is representative of the process variable (PV), is then fed into the microprocessor conversion portion. Process sensor ADC Micro Processor DAC INPUT SECTION

9. In this section, the calculated mA value corresponding to the process vector is fed into a Digital to Analog Converter, which converts the mA value into a real 4-20mA electrical signal. A smart transmitter using the   HART protocol has a microprocessor that manipulates the device data instead of a solely mechanical or electrical direction between the input and the resulting 4-20 mA output signal as received in traditional analog transmitters. OUTPUT SECTION This section contains a microprocessor whose primary purpose is to convert the process vector to the process's mA representation mathematically. The microprocessor is directly linked to the memory where the transmitter assembly, initialization, and diagnostic data are stored. Conversion SECTION

10. Hart Transmitter Block Diagram

11. How HART Transmitter works ? The HART Protocol employs the Frequency Shift Keying (FSK) standard to superimpose low-level digital communication signals on top of the 4-20mA signal. This enables two-way field communication and allows additional information to be communicated to/from a smart field instrument in addition to the normal process variable. The HART Protocol transmits data at 1200 bps without interfering with the 4-20mA signal, allowing a host application (master) to receive two or more digital updates per second from a smart field device. There is no interference with the 4-20mA signal because the digital FSK signal is phase continuous. The HART Protocol provides two simultaneous communication channels: the 4-20mA analog signal and a digital signal. The 4-20mA signal uses the 4-20mA current loop, which is the fastest and most accurate industry standard, to transmit the primary calculated value (in the case of a field instrument).

12. HART Communication Protocol Bell-202 standard (FSK) bit ‘1’ 1200 Hz bit ‘0 ’ 2200 Hz Transfer Rate 1200 bit/s Signal Structure : 1 Start bit 8 Data bits 1 Odd parity bit 1 Stop bit

13. HART Networks HART devices can operate in one of two network configurations - point-to point multidrop.

14. Point-to-Point In point-to-point mode, the traditional 4–20 mA signal is used to communicate one process variable, while additional process variables, configuration parameters, and other device data are transferred digitally using the HART protocol . The 4–20 mA analog signal is not affected by the HART signal and can be used for control in the normal way. The HART communication digital signal gives access to secondary variables and other data that can be used for operations, commissioning, maintenance, and diagnostic purposes.

15. Primary and secondary masters The HART Protocol provides for up to two masters (primary and secondary) This allows secondary masters such as handheld communicators to be used without interfering with communications to/from the primary master, i.e. control/monitoring system.

16. Multidrop It is a burst communication mode, where only one slave device is used to broadcast a HART reply message. This mode of HART communication uses only a pair of wires. If possible an auxiliary power supply and safety barriers may also be added. All process variables are digitally transmitted. All field devices in this mode have polling addresses >0. The current is fixed at 4-20 mA.

17. How are HART instruments calibrated ? Calibration of an analog transmitter is fairly straightforward. Following an As-Found test, the zero and span adjustments may be used to set the correct relationship between the input signal and the 4 – 20 mA output. An As-Left test completes the calibration.

18. How are HART instruments calibrated ? The second stage is a computational stage . The Instrument out which is nothing but the output trim. The sensor input stage sets the relationship between an input sensor and the PV, or primary variable. There are three distinct stages for the HART calibration:

19. Hart Transmitter Calibration

20. ZERO ERROR ( Constant all over the range)

21. Calibration of individual error Span Error Zero error

22. Calibration for Zero and Span Zero Adjustment Zero Adjustment Span Adjustment Span Adjustment Zero Adjustment Zero Adjustment Zero Adjustment Span Adjustment Span Adjustment

23. Accuracy  and  stability of HART instruments  does not eliminate the need for calibration. Is HART Calibration Required? Calibration interval  should  be set short enough to insure  that an instrument never drifts out of tolerance. Calibration can not be accomplished by re-ranging field instruments

24. Pros The digital signal in the HART transmission is relatively slow. The analog signal is not available The number of devices that can share the transmission line is limited. Integration with other protocols and standards is necessary. Cons Advantage of conventional 4-20 mA standard. Broad selection availability of HART products Compatible with host applications and devices. Preferred choice for multi-variable instruments Commonly used with smart-field devices.   Of H ART

25. The HART applications Millions of HART-enabled devices are used in process automation and other industrial applications.  More than 250 member companies of the HART Communication Foundation that have their HART-enabled products in the market. As the HART uses the older 4-20 mA standard, it has become the  de facto standard for data communication for smart-field devices and grid instrumentation. The wireless HART is also widely used in instrumentation and automation. It allows for the communication of sensor data without complex multiplexing and cable installations. 

26. Even the best instruments and sensors drift over time, especially when used in challenging process applications. Regulatory and quality standards often state the minimum time period for instrument calibration. Economical reasons – measurement of process parameters often has a direct economical effect. Health & Safety – it is essential that regular checks are performed in order to adhere to necessary health and safety requirements. Although a ‘Smart’ Transmitter is advertised as being smart and extremely accurate, there is still a need to calibrate the instruments. The output protocol of a transmitter does not change the needs for calibration. Put simply, calibration must always be a priority due to the following reasons: Is calibr ation of Smart Transmi tter important?

27. How to calibrate a Smart Transmitter ? Sensor Trim Range setting Current trim The smart transmitter  should not be calibrated  just like the conventional analog transmitter calibrate. Analog transmitters are calibrated by applying a physical input and turning the trim potentiometers to adjust the sensor so that the analog output current becomes correct according to the desired measurement range. For smart transmitters calibration is divided into three parts:

28. How to calibrate a Smart Transmitter ? Sensor Trim Range setting For sensor trim, a technician should apply actual physical input signal to the transmitter. For that calibration can be done in the field or at the lab. Typically there are three forms of sensor trim: Zero sensor trim Lower sensor trim Upper sensor trim Range setting is is usually referred to as “calibrated range” or “calibration range”. Transmitter range setting is done without applying input, and therefore can be done remotely from the control room.Range setting is only applicable to the transmitter with 4-20 mA analog output. That is, for 4-20 mA/HART transmitters , not for pure digital solutions.

29. How to calibrate a Smart Transmitter ? Current Trim Current trim is used to correct the transmitter analog output drift. For instance, if the analog output current is 4.13 mA when it should be 4.00 mA, then current trim is used to adjust it to 4 mA. Current trim is used to match the transmitter analog output current to the current input of the analog input (AI) card channel on the DCS. Current trim is only applicable to the transmitter with 4-20 mA analog output. That is, for 4-20 mA/HART transmitters, not for FOUNDATION fieldbus (FF) or Wireless HART transmitters, the reason being pure digital transmitters have no 4-20 mA analog output

30. Cons Improved accuracy and repeatability Long-term stability is improved and required re-calibration frequency is reduced Reduced maintenance cost Easier and cheaper installation Access to remote calibration Ability to store data so that plant and instrument performance can be analysed Fewer spare instruments required Pros As a part of preventive maintenance, calibration or validation can not be avoided, though the transmitters are SMART. &

31. Some Smart Transmitters Manufacturers Foxboro Honeywell Moore Products Rosemount Emerson Process Management SMAR ABB Siemens Yokogawa

32. References https://www.slideshare.net/jamaju56/smart-transmitter https://instrumentationforum.com/t/smart-transmitters-working-principle/6310 https://forumautomation.com/t/basics-of-smart-transmitters/3030 https://www.transmittershop.com/blog/all-questions-on-smart-transmitters-and-their-calibration-answered https://www.slideshare.net/OMKARKALE5/smart-transmitters-hart-protocol https://instrumentationtools.com/how-are-hart-instruments-calibrated/ https://www.coleparmer.in/tech-article/hart-transmitter-calibration

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