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."
Naturally, once devices with embedded intelligence starts chugging along on a regular basis, it's not much of a stretch for their developers to start seeking ways for them to collaborate with others.
For example, Caviro s.c.a. in Faenza, Italy, is a 12,000-member agricultural cooperative that cultivates 10% of the nation's grapes in eight regions, and is Italy's largest wine producer. To guarantee correct management of Caviro's complex range of wines bottled in four facilities nationwide, system integrator S.A.I.I.E in Forli, Italy, recently automated its 480,000-hectoliter storage and bottling facility in Forli, which bottles or packages 6,000 hectoliters of wine each day in bottles, Tetrapacks and bulk bags. During the bottling process, Caviro's operators must continuously monitor how many hectoliters of wine are in each storage vessel because bottling becomes inefficient if they have too many or too few containers for each type of wine.
Because the Forli plant's 124 vessels come in many shapes and sizes, Caviro needed a flexible level measurement solution. It considered using a radar transmitter with a horn antenna, but settled on Siemens' Sitrans LR250 radar transmitters with flanged, encapsulated antennas. They were mounted on the hatch at the top of each tank, which meant that operators didn't need to unbolt them during cleaning cycles (Figure 2).
On the seven automatic outflow pipes that move wine from the vessels to the filling area, the Forli plant added Sitrans F M MAG 6000 flowmeters with Sitrans F M MAG 1100 stainless-steel sensors to monitor flow. Seven Sinamics G120C inverters control pumps attached to the outflow pipes, while Sitrans LVL100 vibrating level switches provide minimum and maximum levels, so operators know exactly when a vessel is empty and when to avoid overfill, respectively. To handle 24 vessels with other vessels mounted directly above them with no room for a radar transmitter, S.A.I.I.E.'s engineers opted for Sitrans P DS III pressure transmitters to continuously monitor differential pressure at the bottom of the vessels, and employ a PLC to convert their readings to volume measurements.
All these level and other instruments were then tied together by a Simatic S7-1500 control system and Totally Integrated Automation (TIA) portal from Siemens. Simatic ET 200 SP I/O system receives radar signals from the instruments, and sends them to a Simatic S7-1500 PLC, which again converts the real-time readings to volume measurements, so Caviro's operators can maintain exact wine mixtures and take precise inventories.
“An advanced instrumentation and control system such as the one provided by Siemens allows us to concentrate on process quality,” says Domenico Dosio, general maintenance, investment and technical service manager at Caviro.
Herman Coello, product marketing manager for radar and ultrasonic level at Siemens, adds that, "The main role of software and algorithms in level devices is to help us avoid picking up unhelpful echoes from our radar and ultrasonic instruments. We need to separate the wheat from the chaff, but this isn't easy because there are so many different shapes, ladders, agitators and other structures in tanks. Because there are so many different echoes, we need algorithms to see through to the real echo and find its position. This used to involve manual mapping to filter out, mask and block the echoes from obstructions, but today's microprocessors, software and algorithms can help determine more quickly if a multiple echoes are valid or not. For example, our Sitrans LUT 400 ultrasonic level transmitter can perform digital filtering to improve echo profiles and eliminate noise, and it has a set-up wizard, so even a less-experienced user can configure it in minutes. In very challenging applications, we even have echo-tracking functions that predict where subsequent echoes will be based on prior position evaluations."
While it's terrific that microprocessors have gained so much speed at less cost, they only become useful in level measurement when specific best practices are codified and added to their programming and operating routines.
"In our case, we add the data and experience captured from more than 100,000 service recordings collected over more than 20 years," explains VEGA's Tischler. "On top of that, we integrate the last two generations of our radar, guided-wave radar and pressure solutions, add the service reporting experience gained from our other sensors, and run all this through our development process to evaluate how new sensors will response in particular situations."
These records are raw values, such as radar echoes, which VEGA examines, and then matches with a return signal for a true level. This data is presented to VEGA's echo decision software, while the sensor is shown the data from the service record file. This allows VEGA to use the old sensor data to develop better algorithms for its new sensors.
"This knowledge allows our sensors to be more easily programmed, and enables us to create measurement solutions for more specific applications, which we've been doing since 2009," adds VEGA's Koenig. "Instead of tweaking sensors, we can implement applications to adjust sensor parameters automatically. This benefits users when they're configuring at start-up, and deciding to measure liquids, solids, crushed rocks, sand, boulders or chemical reactions."
Embedded reaches out
Of course, once an embedded intelligence device looks outward via an industrial network, especially Ethernet and wireless, then most if not all Internet functions are available to it as well.
For instance, Synergy Resources Corp., an independent producer in the Denver-Julesburg (D-J) Basin, eastern Colo., recently needed an automated wellhead and tank-level monitoring solution that was scalable, customizable, cost-effective, and able to interface with an ABB Totalflow Gas Flow computer. The wellpad consists of 11 wellheads, which each required instrumentation to collect data for casing, tubing and surface pressures, as well as monitoring plunger arrival. The pad also had 14 storage tanks, which each required monitoring of product, interface and temperature.
To automate the wellheads and monitor the tanks, Synergy enlisted Five Star Measurement, a service provider in Windsor, Colo., which in turn recommended OleumTech's IO Max wireless transmitters for the wellheads, and a combination of 14 Liquid Level sensors and transmitters for the tanks.
IO Max has four analog inputs (0-10V/4-20mA) for connecting to third-party pressure transducers, which made it easy to monitor the wellheads' casing, tubing and surface pressure. The transmitter also has two discrete inputs for accepting plunger arrival inputs in this application. Its radio frequency (RF) communications have a 10-mile range via the 900 MHz ISM band, and it accepts external 9-24 VDC power, but a solar-powered version was used at Synergy's wellpad. The Liquid Level sensors also mate OleumTech's wireless transmitters using their quick-connect adapters, and this self-contained, internal battery-powered solution has a 7,500-foot RF range and is rated for use in Class I, Div 1 hazardous locations. Likewise, communication between wireless nodes and ABB Totalflow are managed using OleumTech's Wireless Gateway with a Modbus RS485 Serial connection that collects data from 25 field instruments.
Once its wireless wellhead and tank-monitoring solution was designed, Synergy reports that one OleumTech engineer and four Five Star technicians completed the field installation in just one day; didn't interrupt production because no trenching or conduit was needed; and saved at least $30,000 compared to the cost of a hardwired system.
Adonis Reyes, product manager for condition sensing at Rockwell Automation (www.rockwellautomation.com), adds that, "Onboard instrument intelligence is slowly, steadily moving away from hardware-based designs to firmware or software that's easier to update and is a lot more modular. They're also using IO-Link (www.io-link.com) point-to-point serial communication protocol, which can use existing wiring, and is a low-cost method for adding communication and diagnostics. IO-Link also needs less I/O points because it can divide flow and temperature signals on the same channel, instead of using the two I/O inputs that used to be required, and would also need to be converted."
Likewise, VEGA reports it's offering a Bluetooth-compatible version of PLICSCOM modular display and adjustment unit, which allows users to remotely and securely operate a linked sensor via an app. From a safe distance with a device type manager (DTM) on a Windows-based PC, users can immediately set up and adjust sensors using secure, encrypted communications.