Today’s plant engineers and operators have access to such functions as power management, maintenance systems, process automation, asset optimisation, and safety systems. Standards such as NAMUR NE107 are steadily improving the Human Machine Interface (HMI), making it easier to commission, configure, and manipulate instrument parameters.
Benefits of smart instruments
Smart instruments are characterised by:
• Fast, bidirectional digital-communication
• Enhanced sensor, electronics, and process diagnostics
• Increased measurement accuracy under varying operating conditions
• Better record keeping
• Wireless communication capability
With the introduction of intelligent instruments in fieldbus networks, process engineers can now access an increasing array of data that can be used to optimise process performance. Remote configuration and calibration, detailed process variables data and diagnostics are all available at a fraction of traditional costs, without compromising informational value.
The key benefits of smart instrumentation include:
• Scaled process variable: No further scaling is needed outside of the instrument, reducing complexity and the possibility of introducing error
• Self-validation/status: Indication of instrument’s state and health, alerting operators to a change in quality of measurement and potential problems
• Tag-number: Clear P&ID identification of the device within the network, reducing potential errors
• Description: A written definition of the instrument and its application more clearly identifies its role
• Time stamp: Provides a real-time record of process variable information
• Serial number: Can be synchronised with remote instrument life-cycle management systems and maintenance information
• Traceable validation: Indication that device calibration is valid, often addressing ISO 2001 Chapter 7.6
The development of bus communications has drastically increased the amount of transmissible information. Also, bidirectional communication of digital information can take place between a field device and a system, and between field devices.
To make the most of communication improvements and to satisfy more advanced needs, big changes are taking place within field devices, especially those with wireless capabilities.
Currently, potentially valuable information acquired by process instruments is often left stranded in the field. This information could be monitored if a communications pathway back to the host control system were created.
Many instruments have a built-in HART communication protocol normally used during instrument commissioning. With the arrival of WirelessHART wireless adapters, cost-effective and secure communication to remote condition monitoring applications can now be achieved.
By having a wireless communication pathway, plant assets can be maximised, and unplanned plant shutdowns reduced, with both helping to reduce costs and maximise productivity.
Recovered information could include:
• Multivariable process data
• Instrument condition monitoring
• Degrading valve performance
• Sticking valve
• Analyser calibration required
• Low level of pH calibration buffer stock
• Instrument over-pressure counter
• Mass flow and totaliser
• Mass flow and density/temperature
In addition to the measured value, status and alarm messages provide valuable information about plant conditions as well as the reliability of the measured values.
As bus communication supports multivariable transmission, an instrument can transmit multiple measured variables via a single cable compared to traditional analogue transmission systems which require a cable for each variable.
Using a bus communication system enables the transmission of multiple data such as control signals, limit signals, and valve opening signals.
By combining multiple sensor systems, measurement and control capabilities can be expanded to simultaneously measure variables such as pressure, temperature and flowrate, helping to effectively monitor a wide range of applications. With such information made available, outside forces such as environmental effects can be compensated for and process control becomes quicker and more efficient.
Improving DP flowmeter accuracy
A single multivariable DP instrument can measure gauge or absolute pressure, differential pressure, and temperature, overcoming the problems associated with multiple instruments by reducing pipe intrusions and the opportunities for leaks while facilitating regulatory compliance.
Three sources of error exist in a DP flow measurement, specifically:
• Minimising transmitter errors
• Minimising errors in gas and steam caused by pressure and temperature variations
• Minimising primary element errors
Minimising all three sources provides the best accuracy and repeatability.
New smart transmitters can improve performance by considering the effects of the various sources of pressure variability and flow errors that can affect DP flow measurement.
Equipment uptime for continuous production represents an important factor in improving process plant productivity and overall profitability. Smart instruments can play a key role in optimising the maintenance function toward this end.
In some applications, such as power plants, maintenance problems can occur in cases where long impulse lines transfer pressure to remotely mounted pressure transmitters. These lines may plug as often as once a week, which can dramatically affect measurement reliability. Smart pressure transmitters equipped with Plugged Impulse Line Detection (PILD) can quickly alert maintenance departments to measurement problems. In this situation, a diagnostic message can be displayed while sending a digital and/or analogue alarm.
This capability protects the transmitter while offering predictive diagnostics of the pressure measurement loop.
The operating conditions of critically important rotating machinery can also be monitored. Permanently installed sensors make it possible to communicate vibration information continuously. Vibration levels of support machinery can also be measured periodically in the field by plant personnel using portable equipment.
Furthermore, a complete picture of operating conditions can be provided by data processing via health management software. The ability to overlay frequencies, and match fault frequencies to peaks, allows trained personnel to efficiently analyse the data. Alarm reports enable decision makers to quickly evaluate a situation and take appropriate action to prevent a breakdown.
ABB smart instruments follow the NAMUR NE107 “Traffic Light” principle for identifying fault levels, which can be adapted by the customer, depending on the application.
This type of focused asset management supports maximum productivity while incurring minimum costs. Productivity is maximised by adopting predictive maintenance strategies to assure reliability of essential production assets, and by using field-based diagnostics to identify and avoid potential trouble. Careful planning and execution of plant turnarounds minimises their duration and extends intervals between them.
A predictive maintenance program can be expected to bring a 1% to 3% improvement in product throughput, generating enough additional revenue for payback in three to six months.
Despite the numerous benefits of smart instrumentation, there still remains a long way to go before the benefits of field-based intelligence are fully embraced throughout the process industries. However, growing pressure from all the key areas impacting on business today, from tough trading conditions and health and safety issues to energy costs and environmental concerns, are all driving plant operators to look for ways to work smarter. Intelligent instrumentation can help them do that.