Maybe it's all those crystal-clear highballs and free-flowing beverages that make level measurement seem conceptually simple to uninformed observers. However, when they sober up and peer into pitch-black tanks and silos with internal structures, mixers and agitators that must handle viscous and volatile fluids, solids and slurries—not to mention the build-up, dust, vapor, foam and other conditions they generate—well, let's just say accurate level measurement in the real-world is a whole different ballgame.
These challenges have been met by generations of inventive operators, process engineers, system integrators and suppliers, who have developed an array of innovative techniques for precisely determining the level and volume of materials in all kinds of vessels without actually sticking one's head inside them. But, while floats, magnets, pressure transmitters, radar, lasers and ultrasonics get most of the attention, they've all been assisted over the past couple of decades by smaller, faster and less costly microprocessors, increasingly capable software and other forms of embedded intelligence, which can perform calculations internally, or reach out and work via industrial networks that have also grown more capable.
Watch your head
Just as our bony skulls house people's delicate gray matter, the first step in deploying embedded intelligence for level measurement is protecting it for service in often harsh and dangerous environments.
For instance, KGHM International Ltd's mine in Sudbury, Ontario, Canada, crushes five types of copper ore, feeds it into one ore pass, and stores it in a huge underground silo. Unfortunately, ore falling onto the rubber-lined trap door/pass frame at the bottom of the pass was causing excessive damage, which forced KGHM to replace the $100,000 frame too often and experience multi-day downtimes. To maintain a buffer of stationary rock that could act as a cushion, the mine's engineers needed a level measurement down to the bottom of the 225-foot-deep pass, but most instruments couldn't do it due the dust and area dimensions. Also, the rock buffer allowed too much rock in the pass, which could allow different grades to mix unintentionally and cause inefficiencies during processing.
As a result, KGHM installed a Rosemount 5708 3D solids scanner from Emerson Automation Solutions at the top of the pass. The transmitter/sensor uses an acoustic, phased-array of three antennas that generate dust-penetrating, low-frequency acoustic waves, receives time/distance and direction echoes from contents, and penetrated the ore pass's dust and measured to its bottom. This enabled the mine's operators to avoid running the pass frame empty, and ensured the line and pass frame were no longer exposed to falling rocks. Collecting multiple echoes from different directions and distances enables Rosemount 5708 to calculate volume of stored material, and lets its Rosemount 3DVision software generate 3D visualizations of material, while its Rosemount 3DMultiVision software and server let users monitor multiple vessels at multiple sites (Figure 1).
“By installing the scanner, we also minimized the mixing of different ore grades and increased safety,” says Adam Savignac, automation team leader, Sudbury Operations, KGHM.
Market for smarts
To profile some other level measurement users, Control polled close to 150 of them in its March 2017 market intelligence report, "Temperature, Level, Pressure and Flow." The group reported they prefer using differential pressure and radar most often, followed by hydrostatic, ultrasonic and float or other mechanical technologies, while weighing systems, RF admittance or capacitance, and magnetostrictive were also popular (Table 1). Just over half the respondents added that less than 1% of their field instruments have Ethernet communications, while only 5% said more than half their instruments have Ethernet.
"Embedded intelligence devices with level instruments are driven by 24 V DC loops, so we're really looking forward to Power over Ethernet (PoE), which is on the way," says Dean Mallon, national marketing manager for level at Endress+Hauser Inc. "Meanwhile, intelligence inside level devices mainly focuses on the ability to analyze data and increase reliability, such as incorporating multi-echo tracking, which can be especially helpful with free-space radar applications. This method uses a static map of a vessel interior when a radar instrument is installed, and its algorithm generates a dynamic map as the process changes to show how it's performing and ignore upsets. By using the static and dynamic maps, they continually adjust to address process upsets for added reliability. In fact, the settings in an instrument can even be adjusted to monitor foam, for example, which can alert the unit to add an anti-foaming agent on its own without shutting down its process. This means the right decisions get made a lot earlier. "
Similarly, Endress+Hauser recently added Heartbeat Technology to its Micropilot FMR5X free-space radar and FMP5X Levelflex guided radar level transmitters. Heartbeat is an onboard diagnostics and instrument verification system that continuously monitors the status of mechanical, electromechanical and electronic components in the sensor, and sends alerts when it detects a problem. Alerts are sent in accordance with NAMUR recommendation NE 107 and are displayed at the device or at the PLC/DCS. Its built-in diagnostics can detect process problems, such as build-up or foam before failure occurs.
Heartbeat also performs device verifications in accordance with requirements of the pharmaceutical, food and beverage, oil and gas, chemical and other industries. Such requirements call for level instruments to be removed and calibrated unless in-situ verification proves the device is operating properly. During verification, Heartbeat compares internal components with their reference values, which determines device status. Verification produces a pass/fail statement, and generates a verification report in compliance with quality, safety and regulatory requirements, and meeting the needs of agency auditors. Verification information, reports, diagnostics alerts and instrument data can be viewed at the control and monitoring system, or via a web browser running on a PC, tablet or smartphone.
Heartbeat reduces the need for onsite adjustments requiring the removal of instruments from the process; improves product throughput; immediately alerts operators when an instrument requires service; and provides diagnostics functions to describe problems so technicians know what they are dealing with before they go to the field.
"To further simplify these tools for level, we also have two software wizards that take users through the six basic configuration steps for installing Heartbeat's foam detection and build-up detection features," adds Mallon.
Chips for brains
Just as microprocessors everywhere have decreased in size and increased in power, their counterparts in level instruments have followed suit. "We've had intelligent chips in level devices for 20 years, but the old ones were bigger, slower and couldn't process as much data," says Gregory Tischler, product manager for radar and guided wave radar sensors at VEGA Americas Inc. "Now, they're able to gather more information, perform diagnostics, and provide more value. Their data usually comes in two streams: production information and diagnostics about the device itself. We still don't have an Ethernet standard for field devices or sensors, but it would be good if we did."
More recently, these "inside experts" are living up to their names by incorporating algorithms that integrate the best practices of veteran process engineers, perform beyond the usual setpoints and parameters, and analyze and respond to a much wider range of process conditions. Plus, just as users have always sought to mask known obstacles in their vessels to prevent false indications, embedded data processing and software is being used to identify and account for more obstacles impeding true readings.
"Microprocessors have gained huge increases in memory and capacity for many years in accordance with Moore's Law," adds Patrick Koenig, product manager for signal conditioners, indicators and software at VEGA Americas. "This has improved data acquisition, historian and trending functions in radar level and sensors, and enhanced their diagnostics and reliability."