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SPECIAL REPORT
2017 STATE OF TECHNOLOGY
LEVEL MEASUREMENT
VEGAPULS 69 is designed specifically for level measurement of bulk solids. Even in dusty conditions, it always provides precise readings. Dust in the silo or buildup on the antenna have no effect.
This radar sensor also features unrivalled focusing at a frequency of 80 GHz. Simply world-class!
www.vega.com/radar
Dust and buildup on the antenna? No problem!The future is 80 GHz: a new generation of radar level sensors
Wireless adjustment via Bluetooth with smartphone, tablet or PC. Compatible retrofit to all plics®
sensors manufactured since 2002.
TABLE OF CONTENTS
www.controlglobal.com
2017 State of technology: Level measurement 3
Liquid radar level moves up to 80 GHz 5
Radar level adds abilities 8
Density delivers in-process analysis 15
Level switch safety; level for flow 23
Resource guide: The latest in level measurement 28
AD INDEX
ABB 27
Acromag 22
Endress + Hauser 4
Krohne 7
Kobold 14
Vega Americas 2
Delivering true innovation in flow measurement
Proline Promass Q 300/500Premium accuracy in challenging applications
• Exceptional density measurement performance under real-world process conditions (liquids: ±0.0002 g/cc)
• “Multi-Frequency Technology” (MFT) for superior accuracy when metering liquids with entrained gas
• Widest useable flow range on the market – 20 to 60% better than competing devices
• Superior repeatability for custody transfer and meter proving applications• Lowest sensitivity to changing process pressure and temperature
on the market• Heartbeat Technology™ for a device verification during operation
www.us.endress.com/Promass-Q300www.us.endress.com/Promass-Q500
Endress+Hauser, Inc2350 Endress PlaceGreenwood, IN [email protected]
www.controlglobal.com
2017 State of technology: Level measurement 5
Noncontact radar level technology is widely used, offering accuracy to 2 mm, range
approaching 200 meters, and tolerance of extreme pressures and temperatures
with high sta-bility, no moving parts and little maintenance. Steady improvements
in signal processing that allow it to accommodate a broad range of vessels and process
materials, along with reduced power consumption (including two-wire versions that operate
on 4-20 mA) and lower costs have made it the first choice of many instrument specifiers for
liquid level.
But conventional noncontact radar is restricted to 26 GHz, which leads to compromises in
antenna size and beam angle that limit its ability to accommodate foam, buildup and spuri-
ous reflections from mounting fittings, tank walls, baffles, agitators and heaters, especially
in tall, small or narrow vessels. This 26 GHz frequency also reflects poorly from some liquids,
as well as many solids, which reduces sensitivity.
These limitations are most apparent in solids level measurement, prompting engineers to
wish for higher frequency. In the past few years, the FCC has granted this wish by allow-
ing the 80 GHz band for certain low-power applications, including automotive distance
measuring systems (for collision-avoidance and interval control) as well as radar solids
level sensors.
Liquid radar level moves up to 80 GHzNarrower beams, smaller antennas and higher sensitivity handle compact, cluttered or non-conductive applications.
by Paul Studebaker
www.controlglobal.com
2017 State of technology: Level measurement 6
Along with resulting economies of scale, the
pleasing performance of 80 GHz solids sen-
sors has invited instrument makers to adapt
them for difficult liquid applications. One
of the first to do so is Vega, which reports
its new VegaPuls 64 is “the first radar level
gauge on the market for liquids that mea-
sures at a frequency of 80 GHz.”
Higher frequency allows tighter focusing of
the radar beam, so it can avoid interference
with obstacles such as heating coils, baffles
or agitators. A radar sensor with a transmis-
sion frequency of 26 GHz and an 80 mm-
diameter antenna is limited to a beam angle
of approximately 10°. With an antenna of
the same size, VegaPuls 64 has a beam
angle of only 3°. At any given distance, a 3°
beam is about one-fourth the width of a 10°
beam, which allows the sensor to be used in
vessels with internal installations or heavy
buildup on the walls because its focused mi-
crowave beam can be positioned to avoid
the obstacles.
The narrower beam also allows the sen-
sor to fit in nozzles or standpipes, such as
those often used to access buried tanks, or
to make sensors accessible to tank rooftop
walkways, where a conventional sensor
beam gives spurious reflections by striking
the nozzle walls and flanges. It also allows
a ball valve to be installed between the
sensor and the vessel, so the sensor can be
safely isolated or removed for service.
Alternatively, the higher frequency can be
used to allow a smaller antenna. The 80
GHz VegaPuls 64 antenna is approximately
the size of a quarter (3/4 in.) instead of a
coaster (2-3 in.) at 26 GHz, which allows it
to be used in compact process fittings for
confined spaces in small vessels. The small
sensor size also allows applications in pilot
plants and laboratories, where conventional
radar sensors won’t fit. It also performs ac-
curate measurements closer to the antenna
without “ringing.”
The 80 GHz sensor also has a broader dy-
namic range, which improves measurement
certainty, and makes it suitable for a wider
range of applications. Where a 26 GHz sen-
sor would be limited to 96 dB, the 80 GHz
sensor can be set at 120 dB, which is 200
times as sensitive. Media with very poor
reflective properties, such as those with a
low dielectric constant like oil and liquefied
natural gas (LNG), can now be measured
with more certainty, and the sensor can be
tuned to accommodate a broader range of
foam, turbulent product surfaces, conden-
sation or buildup on the antenna.
The availability of 80 GHz radar is not only
raising the level of safety—and allowing the
next step toward self-driving cars—it’s com-
ing to keep an eye on your more difficult
liquid level applications.
Safe and accurate level measurement in chemical and petrochemical applicationsOPTIWAVE series – technology driven by KROHNE
• New 24 and 80 GHz FMCW radar level transmitters for liquids, pastes and solids in process and storage applications
• Over 28 years of experience with FMCW radar technology: from basic applications to agitated and corrosive liquids in narrow tanks with internal obstructions
• Measures media with dielectrics ≥1.4, process conditions up to +200 °C / +392 °F and 100 barg/ 1450 psig
fact
More facts about our new radar portfolio: www.us.krohne.com/radar
products solutions services
ft
bbl
tcf
gal
www.controlglobal.com
2017 State of technology: Level measurement 8
Radar level adds abilitiesInnovations like 80-GHz, combined functions, onboard algorithms and wireless help radar level measurement handle multiplying applications.
by Jim Montague
The overall physical characteristics of liquids, gases, slurries, intermediates, solids and
aggregates don’t change much, so it might seem like the methods for measuring
their levels in tanks and other vessels wouldn’t evolve much either. It’s a logical as-
sumption, but it’s wrong.
This is because many refinements in level measurement like beam-narrowing 80-GHz non-
contact radar and improved guided-wave-radar (GWR), as well as supporting technologies
like wireless and improved communications, are enabling more accurate level measurement
and safety indications for more difficult, liquid/solid, foamy, multi-layered and vapor-blan-
keted substances in more challenging locations.
“Oil and gas prices are down, but that doesn’t mean production can stop, so users need
to increase efficiency by putting level measurement data on their networks,” says Herman
Coello, level marketing manager at Siemens’ (www. siemens.com/us) process instrumenta-
tion group. “This requires fewer people, and prepares users for added profit when prices go
back up.”
NARROWER BEAMS, CAPABLE CHIPS“There are more innovations in level measurement and increasing use of communic-
aions, but we’re also seeing high-cost technologies coming down to price levels where
www.controlglobal.com
2017 State of technology: Level measurement 9
they’re more reasonable for suppliers to
put in products at less cost. This means
more users can employ them, reduce total
cost of ownership (TCO), and achieve
safer, more reliable operations,” says Dean
Mallon, U.S. product manager for level at
Endress+Hauser (www.us.endress.com).
“For instance, we’re leading in innovat-
ing with 79-GHz, free-space radar, which
uses frequency-modulated, constant-wave
(FMCW). This non-contact technology has
been around for many years, but it was
cost-prohibitive until component and ma-
terial costs began to come down recently.
This is why 6-GHz or 26-GHz pulsed radar
was traditionally used for level measure-
ment.”
Mallon explains that 6 GHz is a lower,
broader frequency, so it’s better at pene-
trating steam and vapor, while 26 GHz can
get down to about a 12° beam, which is
cost-effective and has an encrypted Blue-
tooth link within 33 feet. “However, pulsed
is different than FMCW, and can only do
on, off and time gaps, while FMCW is a
constant wave that amps up and down,
achieves tighter, more focused energy,
and allows 79 GHz to create its narrower,
3-4° beam,” he says. “This means a better
signal and more reliability on the reflec-
tion, so it can get into more substances,
and avoid increased dispersal and absorp-
tion issues. However, there are so many
variables, such as vessel height, agitation,
foam and others, that we still need to test
to determine which solution is best for
each application.”
Coello adds that Siemens’ Sitrans LR560
79-GHz, non-contact radar level compo-
nents are popular in the grain industry
because their 4° signal is so focused that
they’re essentially unaffected by sidewalls
and structural supports, but still provide
continuous and dependable level mea-
surements.
“Many users didn’t have automated level
measurement before, and could only make
sporadic, manual measurements,” adds
Coello. “Now, they can tell what’s in their
tanks and silos all the time. Also, because so
many older engineers and operators are re-
tiring, we’re making level devices as easy as
possible to use, so younger personnel don’t
have to be experts to configure them.”
MULTITASKING FOR REDUNDANCYTo reliably measure levels of flammable
liquids and prevent overfills, chemical
manufacturer and toll processor KMCO LLC
(http://kmcollc.com) in Crosby, Texas, re-
cently employed continuous measurement
and high-level switches in tandem on some
of its tanks. However, because these efforts
can be hampered by space limits and added
costs of multiple process connections, it
asked Magnetrol (www.magnetrol. com)
for both technologies to be included in one
3-in. flange process connection. Open com-
munication and accurate feedback allowed
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2017 State of technology: Level measurement 10
this combined design to be accommodated.
GWR was chosen for continuous level, and
paired with an ultrasonic gap switch for
high-level indication. Both technologies
are suitable in Safety Integrity Level (SIL) 2
loops. And, since KMCO also wanted wire-
less communications, both level devices
were seamlessly integrated into a third-par-
ty wireless transmitter.
“Because of turnover of multiple prod-
ucts in the tanks, finding the right fit for a
level transmitter was difficult,” says Daniel
Charles, engineering manager at KMCO.
“Our initial order was roughly 20 Magnetrol
Eclipse 706 GWR transmitters. We were able
to set them up in the shop, and install twice
as many transmitters in half the time as com-
peting models. The key to this is the 706 dis-
play, which we can navigate through quickly,
and ensure that our setup is accurate.”
After installing the 20 units, Charles asked
Magnetrol engineers if they could also fit
a level switch in the flange assembly. “Our
tanks have only one or two process con-
nections on top, and using two ports for
level indication is difficult,” explains Charles.
“We use switches in all of our tanks to give
operators redundant communications to
prevent overfilling a vessel. KMCO is very
focused on health, safety and environment
(HS&E), and we take any step we can to
prevent errors. Magnetrol got back to me
with a design quickly, and we purchased the
first batch of these units. The install was just
as easy as with the 706s—all five were up in
a day. These are now our go-to level trans-
mitters, and they’ll be put on any future
tank level project.”
Bob Botwinski, senior global product man-
ager for radar and GWR at Magnetrol, adds,
“There are very few companies in the pro-
cess industries that haven’t been affected by
low oil and gas prices in recent years. With
that in mind, Magnetrol and others suppliers
are concentrating more on chemical, power
and other industries. In addition, new prod-
ucts and solutions such as KMCO’s are help-
ing Magnetrol to diversify. Since releasing
the first two-wire, 4-20 mA, loop-powered
Model 705 GWR transmitter in 1998 and the
most recent Model 706 GWR transmitter in
2013, we’ve been focusing on other tech-
nologies. In fact, this past January, Magnetrol
introduced two new products: Model R96
non-contact radar transmitter and Jupiter
“On the face of it, level seems like a fairly straightforward measurement—it’s not, and is fraught with application-specific issues that mean many technologies aren’t suited to those applications.”
www.controlglobal.com
2017 State of technology: Level measurement 11
JM4 magnetostrictive transmitter. Both of
these transmitters are built on the Model 706
platform, and all have an intuitive user inter-
face and proactive diagnostics.”
Beyond new products, Botwinski adds it’s
just as important to talk to potential us-
ers about how these technologies can help
solve their level measurement problems.
“Magnetrol offers numerous level sensing
technologies, so we don’t have to force fit a
product into an application. Different tech-
nologies offer different advantages, which
can often open people’s eyes to unusual
conditions in their processes they didn’t
know existed.
This is part of the reason why GWR and
non-contact radar are becoming standard
in industries worldwide,” he adds. “Back in
the 1990’s, non-contact radar was thought
to be the technology of the future. At that
time, when GWR was introduced with its
probe contacting the process medium,
it was not thought to be revolutionary.
However, the probe, originally considered
to the weakness with GWR, has instead
shown itself to be a major strength due to
its signal reliability through vapors, foams
and other difficult situations. More recently,
radar level devices have added diagnos-
tics and other proactive capabilities like
automatic waveform capture to help users
minimize downtime. Now, when a diagnos-
tic event occurs at 1 or 2 a.m., level trans-
mitters can automatically save date and
time-stamped wave-forms and other data
that can be used for troubleshooting.”
BENEFITS FROM BIOMASS One primary reason why accurate level
measurement and distributable data are so
crucial is that many process applications
have grown increasingly varied and non-tra-
ditional, so they need better data to main-
tain efficient control and operations. For
instance, Drax Power Station (www.drax.
com) in Selby, North Yorkshire, U.K., oper-
ates a multi-million-pound, co-firing facility,
which burns low-carbon biomass alongside
coal, enabling Drax to produce 12.5% of its
electricity from sustainable materials and
reduce CO2 emissions.
The biomass facility receives, handles, stores
and processes a variety of biomass materials,
which are injected directly into Drax’s coal-
fired boilers. These feedstocks vary from
forestry residues to cultivated products,
such as Miscanthus and Willow, to agricul-
tural byproducts like straw. The plant’s stor-
age facility includes two 12,000-cubic-meter
silos, which must ensure the biomass is kept
in optimum condition before use. This is
important because biomass is lighter and has
fluctuating handling properties and gener-
ally lower variable-bulk density. This requires
larger storage facilities and presents other
challenges, such as careful stock rotation/
retention time to avoid degradation during
the typical 24-48 hours before it’s sent to
the boilers.
www.controlglobal.com
2017 State of technology: Level measurement 12
Drax reports its biomass silos are centrally
filled by conveyors from railcars, and are
emptied by rotary screw dischargers at
their bottoms. This constant filling and dis-
charging creates an uneven surface, which
requires long-range level measurement,
and reliance on non-contact radar level
transmitters to avoid fouling and wear. As
a result, Vega (www. vega.com) was asked
to install its VegaPuls 68 non-contact radar
level transmitters for solids, working over a
range of approximately 27 meters (Figure
1). Two units are installed on each silo to
provide average reading and dual-redun-
dancy level measurement of the biomass.
The transmitters are mounted toward the
center of the silos, and aimed down and
slightly outward to measure at an approxi-
mately half-radius point for good aver-
age level reading over the surface profile.
Though the conveyor fill point is close, Vega
reports its units work regardless of the fill-
ing stream. It adds there’s no crosstalk with
VegaPuls, even with multiple units in the
same silo, due to dedicated pulse sampling
filters. Drax adds the units have worked
reliably for several years; provide data that
facilitates available filling capacity for the
rail transport department; and deliver stock
supply data to the plant’s control room to
further optimize biomass supply.
WELLNESS WITH WIRELESSBeyond delivering operating and mainte-
nance benefits, radar level measurement
and its supporting technologies can also
aid process safety efforts. For example, a
petrochemical tank storage provider with
facilities in several cities along the Yangtze
River in China uses radar for continuous lev-
el measurement. However, a new standard
for level monitoring recently recommended
using an independent, overfill-prevention
sensor for tank storage. As a result, because
the provider’s engineers supported the
standard, they decided to implement side-
mounted Rosemount 2160 WirelessHART
vibrating-fork level switches from Emerson
Process Management (www.emersonproc-
ess.com) on the sides of their fixed-roof
storage tanks (Figure 2).
The tank provider installed 37 Rosemount
2160s to provide overfill protection with
high-level alarms throughout its facil-
ity, which ensures an extra level of safety
without the cost of added cabling. Data is
collected by a Rosemount 1420 gateway
OPTIMIZE BIOMASS POWERFigure 1: The two 12,000-cubic-meter biomass storage silos at U.K.-based Drax Power Station use Vega’s VegaPuls 68 non-contact radar level transmitters over 27 meters to optimize constant filling and discharge operations, helping the coal-fired station produce 12.5% of its electricity from sustainable materials and reduce CO2 emissions. (Source: Vega and Drax)
www.controlglobal.com
2017 State of technology: Level measurement 13
that interfaces with the company’s PLC via
Modbus communications. The level switches
also provide remote diagnostics, and mini-
mized installation costs because they didn’t
require cabling. The engineers report they
observed the potential of migrating to wire-
less, and add that this application was a
simple way to evaluate, learn and keep up
with advances in instrumentation.
“On the face of it, level seems like a fairly
straightforward measurement—it’s not, and
is fraught with application-specific issues
that mean many technologies aren’t suited to
those applications,” says Tim Chettle, electro-
mechanical business unit director of Emer-
son’s Rosemount Measurement division. “Our
customers can’t be experts in everything, and
that’s why we encourage them to talk with
us first. For instance, wireless instruments
offer many examples of applications where
customers have reaped large installation cost
benefits. Our latest instruments have a host
of on-board, self-checking and status diag-
nostics, which allow users to optimize mainte-
nance routines, saving further costs.”
PREDICTIVE, EASIER FUTUREFinally, Mallon reports that
Endress+Hauser’s GWR and non-contact
radar devices are also accomplishing pre-
dictive measurements thanks to on-board
microprocessors running algorithms in con-
junction with predefined parameters. These
can help keep level applications operating,
predicting process upsets before the loss of
echoes. Contained in preconfigured diag-
nostic software blocks, predictive param-
eters can include electronics temperatures,
voltage inputs, near-field/by-horn measure-
ments, or relative echo amplitude, which is
the strength of a returning signal.
“If the foam in a beer tank is very thick and
we can’t get an echo, then we can monitor
the relative echo amplitude,” says Mallon.
“If its typical measurement decreases 10%
due to foam, then we’ll know it’s happening
again when we see that decrease. Previous-
ly, when a unit signal failed, operators had
to wonder why the echo was lost, and go
and find out. Now, we know what’s going
on, and can predict measurements before
we lose a signal, run an output to a variable-
frequency drive, and more accurately and
reliably maintain level areas.”
WIRELESS AVOIDS OVERSPILLSFigure 2: A petrochemical tank storage facility along China’s Yangtze River uses 37 Rose-mount 2160 WirelessHART vibrating-fork level switches from Emerson Process Management on the sides of tanks monitored by its non-contract radar level transmitters to provide independent overfill prevention sensors and alarms. (Source: Emerson Process Management)
www.controlglobal.com
2017 State of technology: Level measurement 15
Density delivers in-process analysisLevel, flow and density instrumentation offer cost-effective ways to assess process fluids.
by Paul Studebaker
Insitu density measurements have long been useful in process control applications from
recycling nuclear fuel and refining oil to measuring beverage proof or degrees Brix (°Bx)
sugar content of an aqueous solution. Density measurements can provide real-time de-
terminations of concentration, blending ratio, fermentation or oil API (American Petroleum
Institute) gravity, which measures oil heaviness or lightness, etc. These can be used to ad-
just process variables and optimize throughput, quality, equipment and material utilization,
and energy efficiency.
So, it’s no surprise that densities of liquids, slurries and mixtures in vessels and pipes have
been measured for many decades, and density-measurement technologies have been
improved and refined over all those years. Today, in-process density measurements are
commonly performed in vessels using servo gauges, differential pressure (DP), tuning fork
instruments and sometimes radiometry. Flowing measurements can be done with radiom-
etry and with Coriolis flowmeters.
Here’s an overview of real-time, in-process density measurement methods, with recent de-
velopments that might inspire additional or improved instrumentation.
DENSITY FUNDAMENTALS BUBBLE UPDensity is defined as mass per unit volume, typically grams per cubic centimeter (g/cc),
www.controlglobal.com
2017 State of technology: Level measurement 16
but is often expressed in specialized
units such as specific gravity (as a ratio
to a standard such as water), API gravity
(where 10 is the same as water), degrees
Brix (specific gravity converted to sugar
content), proof (calculated to reflect the
percentage of ethanol), etc. The fact that
the fundamental units of density—mass
and volume—are simple (if not always
easy) to measure makes density attrac-
tive as a direct and indirect measurement
of attributes that might otherwise require
complex and expensive analyzers.
Since most fluids expand and contract
significantly with temperature changes—in-
dependent of the parameter of interest—
the temperature of the fluid must often be
taken into account when calculating prop-
erties. Measurements taken under signifi-
cant pressure or vacuum may also require
compensation for pressure-related density
changes.
For example, for years, concentrations of
acids in nuclear fuel recycling were mea-
sured by bubble tubes (Figure 1). By im-
mersing a glass tube to a known distance
below the surface of the acid solution in a
vessel, providing a very small flow of pres-
surized gas to form intermittent bubbles,
and measuring the gas pressure, engineers
could determine the pressure exerted by
the liquid above the bubble. With tem-
perature and, if necessary, ambient pres-
sure correction, they could measure the
fluid density and, hence, acid concentra-
tion. Only the bubbler tube was exposed
to the corrosive and possibly radioactive
process—the gas pump/supply and pres-
sure instrumentation could be placed at a
distance.
Another way to weigh the volume of a
liquid is by using a displacer—a float that
doesn’t float. The displacer can be lowered
using a servomotor and cable into and
through the fluid, and the force required to
support the float and cable can be mea-
sured to determine the weight of the dis-
placed fluid.
“A servo gauge and displacer is often used
Flow control
Purge gasP0
∆P
h Purge tube
Fluid ofdensity ρ
ARCHIMEDES WOULD APPROVEFigure 1: Bubblers have been used to mea-sure densities of liquids by immersing a glass tube to a known distance below the surface, flowing pressurized gas to form intermittent bubbles, and measuring the gas pressure.
www.controlglobal.com
2017 State of technology: Level measurement 17
to detect density interfaces in tank farm
and crude oil applications,” says Gene Hen-
ry, business manager, U.S. level products,
Endress+Hauser (www.us.endress.com).
The displacer can be lowered to detect the
liquid level, then lowered through the liquid
to detect interfaces between layers, includ-
ing the level of any water in the bottom of
the tank. “The gauge can report the density
of each layer. If needed, the density can be
corrected for temperature with the input
from a multi-point temperature probe,”
Henry says.
HYDROSTATIC AND DIFFERENTIAL PRESSUREPressures at known fluid depths are com-
monly used to measure level and/or den-
sity, either by a single measurement (hy-
drostatic) or by the difference between
two measurements (differential pressure,
or DP). Bear in mind that a pressure sen-
sor at a depth can’t tell whether a pressure
change is due to a level change or to a
change in density—to determine one, the
other must be held constant or compen-
sated using an additional instrument.
“Hydrostatic level, using one pressure sen-
sor, requires the fluid have a known density
or specific gravity, so density changes intro-
duce error,” says Jeff Brand, product man-
ager, pressure, Vega Americas (www.vega.
com). Adding a second sensor in the fluid
at a known height above the first provides a
DP measurement, and allows density to be
calculated.
“DP for density is usually used on open-ves-
sel applications such as flotation cells, mud
pits and shakers on mud processing units
where a vapor pressure would not interfere.
Of course, both sensors must be immersed.
In a pressurized tank, you can still calcu-
late density but not level, as the instrument
can’t tell the difference between a pressure
and a level change.”
Instruments are available to mount on
the outside of a tank or through the top.
“They’re immune to effects from agitation,
foam or obstructions,” Brand adds.
The relatively low cost, simplicity and
proven technology of DP has led to wide-
spread use. “Everybody knows how to
calibrate a pressure sensor,” says Nathan
Stokes, product manager, DP level, Emer-
son Automation Solutions (www.emerson.
com/en-us/automation-solutions). “How-
"Sensitive equipment can be fine when the process is running at status quo, but getting there can cause damage."
www.controlglobal.com
2017 State of technology: Level measurement 18
ever, the span of DP for density is on the
lower side. And if you use a DP cell, there
are challenges of impulse piping (leaks,
plugging, fluid evaporation), with remote
seals, and with error due to temperature
changes affecting the density of the fill
fluid.”
More recent developments include electron-
ic systems to measure DP (Figure 2), with
built-in calculations for density and density-
compensated level. “Now, electronic remote
sensors eliminate the need for capillary
tubes. Two separate sensors are mounted
top and bottom to get a single 4-20 mA
signal for DP,” says Stokes. “Eliminating the
mechanical system increases reliability.”
Advances in sensors, seals, electronics,
computing power and diagnostics are in-
creasing precision, improving reliability and
reducing maintenance. “Ultra performance
class” transmitters offer precision to 0.025%
of span, says Stokes. “Sensitive equipment
can be fine when the process is running
at status quo, but getting there can cause
damage—an instrument can be out of spec
from the beginning.” Overpressure protec-
tion allows significant overpressures with-
out drift to withstand startup surges, slugs
and spikes.
DP cell transmitters are being fitted with
advanced diagnostics that can detect
plugged impulse lines. “This is really help-
ful for those wet- and dry-leg applications
where you get sediment buildup in the wet
legs that can solidify, or get liquid buildup in
the dry legs so sensitively is reduced,” says
Wally Baker, content management, pres-
sure, Emerson.
“Diagnostics also monitor transducers
for overpressure, saturation or over-
temperature conditions, so you can know
when these conditions are present,” adds
Baker. “Advanced diagnostics can detect
low voltages or brownouts, and diagnose
power supply or water-in-conduit prob-
lems. That can be built right in via HART or
wireless to give an alarm or notification.”
∆P
L
d
EMBEDDED INTELLIGENCE EMPOWERS DPFigure 2: Electronic remote sensors eliminate the need for capillary tubes. Two separate sensors can be mounted top and bottom to get a single 4-20 mA signal for differential pressure (DP). Built-in calculations provide density and density-compensated level outputs, and eliminating the capillary tubes increases reliability.
www.controlglobal.com
2017 State of technology: Level measurement 19
TUNING FORK MAKES WAVES Another technology that started with level
detection and now does density is the tun-
ing fork-based level switch. “Tuning fork de-
tectors were developed for level, as the fork
frequency in air is different than in liquid.
When a difference of 20% is detected, they
switch the output,” says Endress+Hauser’s
Henry. “But the density of the liquid affects
the frequency, so tuning forks can be used
to monitor density.”
Density also varies with temperature, so you
also need a temperature probe and a den-
sity computer. And you can add a pressure
sensor and input where needed. “The den-
sity computer output can be in degrees Brix
or concentration rather than raw density,”
Henry says. “It can indicate regular vs. high-
test gasoline.”
These instruments are useful in batch opera-
tions, such as blending orange juice from
concentrate, fermenting grape juice, or mak-
ing apple vinegar. “You can tune the recipe
with density, tell when the batch is fermented,
or determine when to stop heating. You can
control proof of rum,” Henry says.
Measuring density directly can have advan-
tages in certain applications. “Acid concen-
tration can be measured with conductivity,
but many acids have a non-linear relation-
ship—with a hump in the curve—so if it’s
way off, you may not be able to tell,” Henry
says. Density has a direct response with
concentration.
CORIOLIS DOES ALL IN ONEWhile DP remains a fine way to measure
density of liquids in vessels, Coriolis flow-
meters have become an increasingly com-
mon way to determine densities of flowing
fluids and mixtures. Capable of extremely
precise and accurate mass flow measure-
ment, the oscillation frequency of a Coriolis
flowmeter’s tubes is inversely proportional
to the fluid density.
With the increasing sophistication and fall-
ing cost of digital signal processing, as well
as lower costs for its demanding physical
construction made possible by mass pro-
duction, Coriolis flowmeter applications
are on the rise. “The best Coriolis meter
can measure to 0.0002 g/cc with no spe-
cial adjustment required in the field,” says
Nathan Hedrick, flow product marketing
manager, Endress+Hauser. “They’re now
commonly used in some cases to measure
density, but many people take advantage of
the multivariable capabilities. From a single
instrument, you can get mass flow, density,
temperature and even viscosity from some
Coriolis meters.”
RADIOMETRY: THE NUCLEAR OPTIONOver the years, some of the most challeng-
ing in-situ density measurement problems
www.controlglobal.com
2017 State of technology: Level measurement 20
have been solved using radiometric (also
called nuclear or gamma) technology,
where the intensity of gamma radiation
from a source on one side of a process
pipeline or vessel is measured using a de-
tector on the other side. The intensity of
transmitted radiation is related to the den-
sity of the process medium.
“The technology is beautiful because
it’s completely impervious,” says Chris
Willoughby, product manager, nuclear,
Vega Americas. “Unlike Coriolis, a bolt-on
solution can be added without modifying
the piping.” Radiometry has been used
for many decades, and proven reliable in
power plants, paper mills and metal ore
processing. It’s suitable for a wide range
of pipe sizes, wall thicknesses and den-
sity ranges, and is especially appropriate
where pipe sizes are 3-4-in. and larger. It’s
typically used for pipe diameters down to
2 in. and up to 36 in., including lined metal
and plastic pipe.
“Radiometry is very prevalent in the mining
industry, where they often combine a mag-
netic flowmeter and a density meter to get
the mass flow of liquids and slurries,” says
Henry. “Those non-intrusive technologies
handle slurries well, without the tortured
path of a Coriolis meter, which can lead to a
lot of erosion.”
Radiometric methods are also used for level
measurement, but usually those aren’t com-
bined with density measurements. “Most
nuclear level applications are on vessels
that are too large to measure density di-
rectly—that’s typically limited to diameters
of 3 ft or less,” says Willoughby. “However,
it can be done by inserting the source in
a drywell with a detector on the outside.
This is commonly performed on separator
processes in refineries using a multi-point
density array. For example, in a desalter
with an emulsion layer, we can put sources
in a drywell, and use external detectors to
generate a density profile to detect changes
associated with an interface.”
The maximum diameter for radiometric
methods depends on the strength of the
radiation source and the sensitivity of the
detector. Because the source is radioactive
material, it’s closely regulated worldwide,
and requires a license to own, install, oper-
ate and service.
"We can put sources in a drywell, and use external detectors to generate a density profile to detect changes associated with an interface.”
www.controlglobal.com
2017 State of technology: Level measurement 21
Advances in detector technology have al-
lowed lower-level sources to handle larger
applications. “The old ion chamber detec-
tors could handle an 18-in. pipe using a
250 mCi Cesium-137 source. Now, using a
scintillator tube with a crystal or PVT [poly-
vinyltoluene] detector, an 18-in. pipe can be
done with 20 mCi,” Henry adds. A crystal
detector is most sensitive, and can use the
lowest-level source.
With the more sensitive detectors, “We can
do more applications with Cesium, which
has a half-life of 30 years,” Henry says.
“Cobalt penetrates through more material,
and is used for the difficult level applica-
tions, but it has a half-life of 5.2 years, which
means the source must be replaced more
often. Today’s detectors can automatically
compensate for this source decay.”
Licensing can be an impediment, so “suppli-
ers will offer assistance,” says Willoughby.
They offer safety training, license services,
consulting on safety programs and auditing.
“They’ll review the user’s license before de-
livery, make sure it’s adequate and suggest
revisions to make it more effective.”
Laboratory analysis may be more precise,
but tuning forks, Coriolis meters, radiomet-
ric and differential pressure methods offer
in-situ measurements. Whatever method is
chosen, in-process density measurement
can be a cost-effective way to improve pro-
cess efficiency, throughput and quality.
“Advances in detector technology have allowed lower-level sources to handle larger applications.”
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www.controlglobal.com
2017 State of technology: Level measurement 23
Level switch safety; level for flowAre piezoelectric switches really safe in hazardous areas? How can we use a level gauge to set a flow alarm?
Q: Are piezoelectric switches really safe in
hazardous areas?
I understand that in the vibrating, tuning
fork-type level switch, a piezoelectric crys-
tal is generating an oscillating frequency.
We have a Class A product stored in a tank,
which requires a Zone 0 installation, and I
need a level switch that is certified for Zone
0. My question is, even when it’s certified
for Zone 0, is the use of such a frequency-
generating crystal design good practice?
Why does a frequency-generating crystal
in not represent a risk in a hazardous area?
What type of protection has been provided
to achieve that?
I understand that intrinsic safety (IS) applies
to wiring and terminals associated with
the enclosure—is the section between the
tuning fork and the enclosure intrinsically
safe? Is the transmission of frequency from
a piezoelectric crystal safe when the switch
is used in an application involving a Class A
product? How is the safety achieved?
M. Ulaganathan, instrumentation design engineer
A: IS certification looks at the energy of the
whole circuit, including wiring and the end
device. All components have to be as-
sessed.
Essentially, the piezoelectric crystal is as-
sessed as an energy storage device (i.e.
inductance and/or capacitance). The energy
storage equations are (1/2)LI2 and (1/2)
CV2. The energy storage of the end device
is added to that from the wiring calculation.
The total energy storage has to be less than
that required for the specific IS calculation. A
www.controlglobal.com
2017 State of technology: Level measurement 24
piezo crystal would not have any inductance,
so all the energy would be stored in the
equivalent capacity.
This is exactly the same as for any end
device (e.g. transmitter, positioner, sole-
noid). Any end device has to be certified to
be IS (except for simple apparatus that do
not generate more than 1.5 V, 100 mA and
25 mW). The certification then provides
the energy ratings for that device, which is
used in the IS calculation. In practice, this
information can come in a variety of ways.
There is a lot of information from the barrier
vendor websites on certification, what the
data means, and how it is used.
Note that the energy is coming from the
power supply in the equipment room. In
this application, the piezo is not generating
power; it is only storing energy. It is moving in
response to applied electrical energy. We are
not vibrating it externally to produce energy.
The most likely hazardous area protection
technique for Zone 0 is IS. Intrinsically safe
designs ensure that the energy level of the
instrument and associated wiring and power
supplies is below the level that would ignite
the potentially flammable atmosphere.
IS is an established design code and prac-
tice. It has been around for more than 40
years and is recognized by the various elec-
trical standards (ATEX, IEC, NEC, etc). The
latest edition of Liptak’s handbook has a
chapter written about the use of instrumen-
tation in explosive atmospheres.
Vendors also provide a lot of literature
explaining various explosion-proofing
techniques. For example, see www.intec-
automatizari.ro/custom_images/Resurse/
Principles_of_Explosion_Protection_2012.
pdf. Also look at the Pepperl+Fuchs website
for their literature.
Simon Lucchini, chief controls specialist and Fluor
Fellow in safety systems, [email protected]
A: The non-scientific response is, if you’re
not comfortable with something, don’t use
it. A device rated for an application should
be safe. A rated device probably requires
special installation requirements for it to be
safe. Installation details must be followed
and the installation inspected by the proper
person. There are plenty of level switches
based on other technologies; you could
look at them and find something you’re
comfortable with.
Cullen Langford, [email protected]
A: If you’re interested, Micronor offers an
inherently safe fiber optic microswitch, model
MR386 (http://micronor.com/products/fiber-
optic-microswitch). The switch is an entirely
passive, all optical, and non-electrical sensor.
The remote controller outputs are inherently
safe optical radiation. A suitable, inherently
safe level limit switch can be constructed us-
ing such a fiber optic microswitch.
Dennis Horwitz, [email protected]
www.controlglobal.com
2017 State of technology: Level measurement 25
Q: How can we use a level gauge
to set a flow alarm?
What is the easiest way to implement a level
decline alarm? We have a tank that supplies
caustic injected to a process. The caustic
flow doesn’t have a flowmeter, but the level
decline is fairly consistent. We want to alert
the operator if the caustic pump suddenly
trips and there is no caustic flow to the
process by using the level decline. How do
we implement an alarm to let the operator
know that the level drop is abnormal? Note
that the level doesn’t stay constant if a pump
trips, as two pumps are operating in parallel
most of the time. We want to alert the op-
erator when at least one pump has tripped.
The level is detected by an electronic
guided wave radar (GWR) transmitter.
There is no pressure transmitter on the
pump discharge, only a pressure gauge.
The level decline (rate of level dropping) is
pretty constant, with the rate being low if
one pump is running, and about double if
two are running.
Yee Kiat, [email protected]
A: If you have a DCS/PLC control system,
the control circuits in the motor control
center (MCC) for the pumps probably have
auxiliary contacts for remote indications.
These can generate alarms to signal if
pumps stop.
You can also use an algorithm in the DCS/
PLC to convert a change of level into a
flow rate, both when one and when two
pumps are running, as volume rate flow.
Alarms could be set for these.
H.S.Gambhir, [email protected]
A: Level is unlikely to be a sensitive method
of detection, as you will have to compare
an “old” reading against a “current” read-
ing of the level sensor. Assuming the tank is
of constant cross-section, you can store a
value and convert it to volume (level*area).
Store this value for (say) one hour, and
repeat the measurement and calculation.
Difference between the two will be an aver-
age flowrate over the past hour. Store the
current value in place of the old value and
repeat. As I said, insensitive.
An alternative, faster method is to fit the tank
with a much smaller diameter gauge tube,
and feed the pump(s) from the gauge tube,
measuring the level from the gauge tube.
Intermittently close the connection from the
tank to the gauge tube and time the drop in
level, then reopen the tank connection. This
does give you an increased risk of failure,
however, as the valve may fail to open.
Why not bite the bullet and fit a magnetic
flowmeter—they are not all that expensive.
Ian H. Gibson, process, control and safety engineering
consultant, [email protected]
A: One of the key rules of measurement
is that indirect measurements are to be
avoided whenever possible. You’re look-
www.controlglobal.com
2017 State of technology: Level measurement 26
ing for flow, not level change. If you want
to alert the operator if a pump has tripped,
then alarm on the run status from the mo-
tor. The power/current measurement of the
motor will give a reasonable indication of
flow from the pump.
I would not use the rate of change; it will be
problematic to set the right time intervals
to do the rate of change. It can either not
alarm when needed or give spurious alarms.
A better solution is to add a power or cur-
rent meter to the motor starter. This will give
an indication of the caustic flow. Since you’re
looking for a change, the absolute accuracy
will not be a problem. The advantage over
the motor run status is that it will detect a
blocked discharge from the pump (i.e. power
will go down). A power meter would be bet-
ter than a current meter since it’s indepen-
dent of the current vs. phase angle charac-
teristics of the motor (for example, some
motors have strange current characteristics
when consuming lower power).
Either a power or current meter are relative-
ly inexpensive, and don’t involve process
plant modifications for installing a flowme-
ter. It is also a direct measurement of flow.
Since the rate of change of level is a
programming exercise, you could just try
it. You can then confirm for yourself if it
gives a reliable/consistent result or not. It
would be a quick and cheap change.
Simon Lucchini, chief controls specialist and
Fluor Fellow in safety systems
A: The best way to do it may be to program
a rate-of-change logic. Some DCSs have
embedded the rate-of-change variable out
of the analogic variable block (PCS7, for
instance). When I do this, I typically cap-
ture several samples in a period of time (for
instance, 10 samples every six seconds), and
then do a minute average with the corre-
sponding time and unit conversion.
If we’re talking about a slow ramp, this can
be done using two samples in a minute. The
program has to consider the pumps run-
ning, and also hold the last value if the tank
is being filled. The tricky part is to have an
accurate calculation of the volume based
on the tank geometry, which can be verified
using a calibration column if available. If the
value needs to be obtained as mass flow,
a density sensor is also needed to convert
volume to mass.
F. Alcala, [email protected]
A: Connect the level transmitter to a con-
troller and generate a calculation of how
fast the level changes based on one or two
pumps operating. That way, the change in
level will be measured against the setpoint,
which is based on the calculated change in
level when the pumps are operating. Set an
alarm setpoint to this rate of level change.
Alex (Alejandro) Varga, [email protected]
—K-TEK LMT level transmittersSimple, reliable, and accurate.
ABB’s new K-TEK LMT series of magnetostrictive level transmitters minimize downtime and help maximize profits. Featuring easy setup for level and interface measurement, the LMT can be mounted internally (LMT 100) or externally (LMT 200). Discover level measurement made easy. www.abb.com/level
www.controlglobal.com
2017 State of technology: Level measurement 28
Resource guide: The latest in level measurement
BOILER DRUM INSPECTION GUIDEThe 2016 edition of Clark Reliance’s Boiler
Inspection Guidelines for Drum Level In-
strumentation is easy to understand and
concisely presents ASME Section I water
gauge inspection requirements for handy,
on-the-job reference by boiler operators. It
includes code requirements for water col-
umns, water gauge valves, gauge glass, re-
mote level indicators, magnetic water level
gauges and water column isolation shutoff
valves, as well as 2015 Code changes and
CSD-1 requirements and recommendations
from Section 7. The guide also lists the most
common non-compliant, drum-level ar-
rangements and solutions. Copies are avail-
able at www.boilerinspectionguide.com,
and free to qualified recipients.
Clark-Reliance Corp.
440-572-1500; www.clark-reliance.com
LEVEL SENSING INTRODUCTIONThe “Level Sensor” article at Omega Engi-
neering’s website covers non-contact ultra-
sonic, contact ultrasonic and capacitance
technologies. It also provides questions to
help choose level measurement sensors,
and answers frequently asked questions. It’s
at www.omega.co.uk/prodinfo/level-
measurement.html#faq.
Omega Engineering, www.omega.co.uk
DP LEVEL FOR ROOKIESThis online feature article, “Beginner’s Guide
to Diffential Pressure Level Transmtters,” by
David Spitzer presents “the not-so-straight-
forward basics of this measurment tech-
nique.” To help users avoid costly mistakes,
it shows readers how to understand DP level
measurement, and its techniquea and limita-
tions. The guide also covers three different
www.controlglobal.com
2017 State of technology: Level measurement 29
techniques used to calibrate pressure level
transmitters. It’s located at http://info.con-
trolglobal.com/differential-pressure-lp
CONTROL, www.controlglobal.com
BASICS OF LEVEL—AND HISTORYThis classic, 10-minute video hosted by for-
mer Control editor Walt Boyers examines all
the essential concepts of measurement, in-
cluding some of its earliest origins in, where
else, Egypt, where floods from the Nile
made early level measurement a necessity.
The video also demonstrates methods for
selecting the correct level technology for
different types of process applications. It’s
located at www.youtube.com/watch?v=-
MQU0xgh6bA.
CONTROL, www.controlglobal.com
ULTRASONIC VS. GUIDED WAVEThis 13-minute video is presented by Jason
Beck of Flo-Corp., who explains the some
of the basic physics and characteristics of
ultrasonic and guided-wave radar technolo-
gies, shows how their capabilities work in
process applications, demonstrates poten-
tial issues with each method, and shows
how viewers can find the most useful solu-
tion for their requirements. It’s located at
www.youtube.com/watch?v=siAMerrbpPU.
Flo-Corp., www.flo-corp.com
OPEN TANK LEVELInitially intended for students at NAIT,
this 17-minute tutorial video demonstrates
how to perform open-tank level measure-
ment with a Rosemount 1151 DP transmitter,
though the methods and concepts pre-
sented are useful for many technologies.
It also covers set up, calibration, system
layout, output wiring, input calibration
and bench calibration hook-up, and other
tasks. It’s located at www.youtube.com/
watch?v=xfo9n_ly8sA.
Northern Alberta Institute of Technology, www.nait.ca
ADVANTAGES AND DISADVANTAGESThe level measurement entry in the Ency-
clopedia of Chemical Engineering Equip-
ment by the Chemical Engineering Dept.
at the University of Michigan’s College of
Engineering covers the many of the main
types of level measurement technologies
with descriptions and photos. However, it
also presents the advantages and disadvan-
tages of each level measurement method.
It’s at http://encyclopedia.che.engin.umich.
edu/Pages/ProcessParameters/LevelMea-
surement/LevelMeasurement.html.
University of Michigan, www.engin.umich.edu/che
CAPACITIVE LIQUID LEVELThis 4.5-minute, blackboard-style video by
U.K.-based Gill Sensors & Controls provides
a quick summary of the primary aspects of
capacitive level sensing, including behavior
of the dielectric, and shows how differ-
ent probe materials can serve the needs of
different applications. It’s located at www.
youtube.com/watch?v=0du-QU1Q0T4.
Gill Sensors & Controls, www.gillsc.co.uk