Measurement techniques: A smart approach

Global process industry losses arising from unscheduled downtime and poor quality amount to $20bn, or 5% of annual production. ARC estimates that almost 80% of these losses are preventable and that 40% are primarily the result of operator error. 

Smart instrumentation combined with asset management can help minimise these losses.

Smart instruments measure or directly affect single or multiple plant variables, contain a microprocessor for processing data, and are commercially available off-the-shelf. Many include not only sensors for measurements and communications, but actuators, valves, motor variable speed drives, and other control equipment. They allow operators and engineers to gain information about the process and the device which was previously locked away.

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

Process engineers are no longer limited to a process variable measurement from a unidirectional 4-20 mA analogue signal. Intelligent instruments in fieldbus networks offer remote configuration and calibration, data beyond process variables, diagnostics, and more. These systems are decreasing the cost of process instrumentation while providing increased informational value.

The development of bus communications has 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.

Wireless possibilities

Potentially valuable information is often left stranded in the field, but could be monitored if a communications pathway back to the host control system were created.

Many existing installed instruments have a built-in HART communication protocol, normally used during instrument commissioning. With the arrival of wireless standards, such as WirelessHART, wireless adapters can be fitted to existing HART instruments, providing a cost-effective and secure communication pathway back to remote condition monitoring applications. With the arrival of battery-powered standalone devices, this capability has been further extended, opening up new opportunities for installing wireless devices in both safe and hazardous areas. 

Current estimates indicate that only 10% of the 30 million HART instruments installed since 1989 have a digital pathway back to the host. Remote digital access would allow operations and maintenance to take full advantage of this stranded instrument information. WirelessHART adapters for field instruments eliminate significant rewiring costs and provide a solution for secondary monitoring applications. 

Multivariable transmission

Developments in multi-parameter sensor technology present a raft of opportunities for plant-wide measurement. Bus communication supports multivariable transmission, enabling a single cable to convey all measured variables from a field device. The same goes for control signal transmission to a positioner for an actuator or control valve, with bus communications able to transmit multiple data such as control signals, limit signals, and valve opening signals.

Many other pieces of information can be used to expand measurement and control capabilities. Combining multiple sensor systems in a single pressure transmitter permits simultaneous measurement of differential pressure, absolute pressure and, via an external sensor, process temperature. 

Asset management

Smart instruments can play a key role in maximising asset availability. In coal pulverising applications in power plants, for example, problems can arise with the long impulse lines that transfer pressure to remotely mounted pressure transmitters.

Frequent plugging of the lines can affect the reliability of measurement. Smart pressure transmitters equipped with Plugged Impulse Line Detection (PILD) can quickly alert maintenance departments to measurement problems. On sensing a plugged impulse line, the transmitter displays a diagnostic message while sending a digital and/or analogue alarm. Alarm reports enable decision makers to quickly evaluate a situation and take appropriate action to prevent a breakdown.

NAMUR standards

The Namur NE107 recommendation enables operators to use diagnostic data from field devices and take appropriate actions as required. 

Focused asset management supports maximum productivity through fast, reliable start-ups, by adopting predictive maintenance strategies to assure reliability of essential production assets, and by using field-based information and diagnostics to identify and avoid potential trouble. Careful planning and execution of plant turnarounds minimises their duration and extends intervals between them. 

Growing pressure from all the key areas impacting on business are helping to drive plant operators to explore ways to work smarter. Intelligent instrumentation can help them do that.