Built-In Condition Monitoring Increases Efficiency

Instrument technicians can use wireless technologies to monitor and manage instruments from smartphone apps, such as Endress+Hauser’s SmartBlue app, without the need to physically open up the instruments and connect other test devices.

Modern smart instruments monitor and transmit large volumes of process and diagnostic data to reduce maintenance efforts and increase uptime.

By Keith Riley, Endress+Hauser

Modern plants use vast installations of instrumentation to continuously monitor and control their processes, with the goal of maximizing operational productivity, product quality, and process/personnel safety. Instrumentation ranges from inline process sensors — directly measuring flow, temperature, pressure, level, and other characteristics of products or ingredients — to safety sensors around the workspace, such as ambient gas detectors.

Although they are critical in modern facilities, all these instruments require time and expertise to install, operate, maintain, and document accurately. Because measurement accuracy can be adversely impacted by changing process conditions, it is common for conventional analog instruments — limited to a single 4-20mA output signal — to fall out of quality compliance without warning. These instruments cannot be adjusted to ambient conditions or proactively signal impending device failures, so they must be regularly calibrated.

To address these and other challenges, modern smart instruments use digital communication protocols and self-monitoring capabilities to provide host systems and plant personnel with process and diagnostic data. This information helps optimize operations, gather additional process data, reduce maintenance burdens, preemptively predict failures, and minimize unplanned downtime.

Left unmaintained, process-plant instrument performance can degrade over time due to adverse and accumulating process conditions, leading to measurement drift. All figures courtesy of Endress+Hauser

Analog limitations

Modern process facilities face increasingly stringent production, accuracy, and safety requirements, and conventional analog instrumentation does not adequately meet these constraints. Many factors can interfere with measurement accuracy, including product buildup, corrosion, bubbles, and sedimentation. Because traditional analog instruments are limited to transmitting a single process value using a 4-20mA signal, they cannot provide any additional information about sensor health or measurement quality. As a result, operators and maintenance technicians must often deduce or guess whether measurements are accurate.

Communication limitations can also inhibit analog instruments from warning about unfavorable issues developing in the process. Left unchecked, these sorts of conditions can cause quality deviations, requiring unplanned downtime to address. In the worst cases, failures can cause severe equipment damage or safety incidents.

Historically, there have been two common choices for instrumentation maintenance: adherence to strict calibration cycles or run to failure. Both strategies have tradeoffs.

Strict calibration scheduling decreases overall production because it requires shutting down the associated process from time to time. While this method reduces the risk of off-spec production, it can increase the risk of failure to individual instruments due to manual removal and installation requirements, which can be prone to systematic errors. Additionally, many of the instruments removed for calibration are still operating within specification.

Run to failure avoids the unnecessary removal of instruments operating within specification, but it comes at the cost of periodic unscheduled shutdowns and maintenance requirements, negatively affecting productivity.

Even with diligent upkeep, instruments are bound to occasionally fall out of specifications without allowing users to determine exactly when the deviation occurred. On the other hand, recalibrating instruments that are comfortably within bounds consumes significant unnecessary effort.

This diagram represents a common digital instrument architecture consisting of field devices, human machine interfaces (HMIs), and intermediary controllers and gateways. Several protocols are used, including HART, fieldbus, Ethernet, and WirelessHART.

Connectivity with digital protocols

Incorporating smart instrumentation into plants facilitates better process operation, management, and optimization by overcoming the challenges posed by analog-only instruments. Modern instruments employ digital communication protocols—such as WirelessHART, PROFINET, EtherNet/IP, and IO-Link—over advanced media, including wired Ethernet cables and wireless pathways, either in place of basic hardwired installation or superimposed on top of this analog infrastructure, increasing capabilities and value.

In applications where hardwiring the transmitters to a host system is convenient, including many facility retrofit projects, the two-way digital HART communication protocol is a good option for improving condition monitoring. This protocol uses traditional 4-20mA wired media, enabling two-way digital data exchange between smart instrumentation and calibration devices or host systems.

Smart instruments can also use fieldbus and Ethernet-based protocols, which offer all the digital capabilities of HART, although they typically operate at much higher speeds, using advanced communication media such as wired Ethernet or wireless connectivity.

When wired connections are impractical, smart instruments can use 2.4-GHz radio-wave protocols, such as WirelessHART. Many smart instruments now come with native wireless support, while others require add-on adapters. In both cases, wireless capabilities can be used to create mesh sensor networks throughout a plant. These types of connections are secure, with encrypted data transfer and password protection preventing unauthorized access. They provide communication redundancy by allowing alternative routing between devices should the shortest path become broken.

Increase insight, control

Regardless of the media and protocol used, digital communication enables each smart instrument to transmit multiple process values, exhaustive diagnostic data, complete calibration information, and more, bi-directionally where appropriate. This enhanced communication provides deeper insight into process conditions and facilitates comprehensive control.

Intelligent plant-analysis systems can ingest this wealth of data to facilitate proactive maintenance and condition monitoring, which reduces unplanned downtime and costs, and minimizes the risk of harm to humans or plant equipment. Instead of waiting for secondary process out-of-compliance alarm notifications or outright device failures, these systems sift through the available data looking for trends that indicate impending problems, and then alert plant personnel. These systems can also provide troubleshooting and maintenance recommendations, guiding technicians through remediation efforts.

Smart instruments may even feature on-board automated and on-demand self-verification, where a series of in-situ tests is performed. A report can then be generated, verifying functional status. These verifications typically exhibit very low undetected failure rates and provide sufficient coverage to justify extending calibration intervals.

In certain applications, condition monitoring can be further extended to include automatic system responses that mitigate the adverse condition. For example, smart-level instruments monitoring surface foam as a secondary process value can provide a direct signal output to activate a defoaming agent without requiring an external controller. Or, for particularly dusty processes, smart instruments can provide output signals to activate solenoid valves controlling plant air when limits are exceeded.

It is often possible to commission smart instruments wirelessly, for instance, by using a smartphone or tablet app connected to the device with Bluetooth. This significantly simplifies commissioning in inconvenient or hazardous locations that otherwise require special certifications for operators to enter.

Endress+Hauser’s Micropilot FMR60B 80 GHz level instrument monitors centrate and foam levels simultaneously in a wastewater treatment facility’s sludge dewatering system. It also activates a defoaming agent when limits are breached.

One large wastewater treatment plant installed an Endress+Hauser, Greenwood, IN (us.endress.com), Micropilot FMR60B Smart 80 GHz radar level instrument to monitor centrate levels in its sludge dewatering system. Because the centrate produced in the dewatering process contains high concentrations of ammonium nitrate, it must be held in a retention tank and gradually released into the wastewater stream. Foam tends to form inside this tank, risking overflow if left unchecked, so careful monitoring is critical to detect foam and activate defoaming pumps, when needed.

Prior to installing the new instrument, the plant required two separate sensors to measure liquid and foam levels, neither of which were suitably accurate. The new sensor now handles both functions, reliably measuring liquid and foam levels simultaneously. It also directly regulates defoaming pumps with a continuous control signal, ensuring they operate at appropriate speeds for handling real-time foam levels. 

This new setup provides the plant with better accuracy for improved efficiency, reduced maintenance needs, lower operating costs, and increased system availability.

At an edible-oil refinery producing high-quality oils in compliance with HACCP food safety standards, pipe systems must be completely free of residues between batches to prevent mixing different oil types. When the system is emptied, tuning-fork level switches are used to detect the presence of any remaining oil. Unfortunately, buildup on the tuning fork is a common issue.

During the refining process, bleaching earth is added to oil at high temperatures to remove contaminants. This mixture of oil and bleached earth tends to accumulate on measuring devices over time. Eventually, this can cause sensors to falsely indicate the presence of oil in a pipe, forcing the refinery to pause production and remove the instrument for maintenance.

The Endress+Hauser Liquiphant FTL51B level switch verifies the refining system is free of oil and performs self-monitoring to detect problematic buildup on the sensor.

To mitigate these problems, the refinery installed Liquiphant FTL51B smart level switches in locations where buildup cannot be visually detected. These devices identify developing buildup, exhibited as a decrease in tuning fork vibrational frequency over time, making it possible to predict when maintenance will be required.

Plant personnel can leverage these predictions to proactively schedule maintenance in advance, reducing unplanned downtime. This saves the plant an estimated 1 hr. of maintenance time for every measuring point/week. Device status can be easily checked in an app with a Bluetooth connection with a standard smartphone or tablet.

Overcome analog constraints

When process conditions degrade, traditional analog instrumentation simply may not provide adequate warnings for plant personnel. However, modern smart instruments provide the tools to overcome these shortcomings, with extended process and diagnostic data, in addition to the ability to warn users of, or locally adapt to, developing issues that can cause failures when left unmitigated.

End users can manage this wealth of data according to plant, enterprise, or industry requirements, ranging from sub-second real-time updates to overall process and diagnostic information history for analysis and review. Additionally, smart instruments provide increased flexibility and operator safety when measuring processes in remote, hazardous, or difficult-to-wire areas.

The digital communication protocols used by smart instrumentation enable extensive data transmission between devices and host systems, providing proactive insight into process conditions, fostering predictive maintenance, and empowering improved process control. These capabilities help facilities maximize production uptime, product quality, and human and equipment safety, ultimately benefiting employee satisfaction and bottom-line profits.

Keith Riley is National Product Manager for Level and Pressure at Endress+Hauser, Greenwood, IN (us.endress.com). He has been with the company since 2008 and has more than 20 years of sales, marketing, and instrumentation experience in the process industries.