2017 STATE OF TECHNOLOGY LEVEL MEASUREMENT...TL ONTENTS 2017 State of technology: Level measurement 3 Liquid radar level moves up to 80 GHz 5 Radar level adds abilities 8 Density delivers

SPECIAL REPORT

2017 STATE OF TECHNOLOGY

LEVEL MEASUREMENT

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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

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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



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.

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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



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



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.”



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.



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)



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)

http://www.koboldusa.com



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),



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.



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."



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.



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



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.”



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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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

[email protected]

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



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]



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-



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

[email protected]

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

http://www.abb.com/level



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

http://www.omega.co.uk/prodinfo/level-measurement.html#faq

http://www.omega.co.uk/prodinfo/level-measurement.html#faq



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

http://info.controlglobal.com/differential-pressure-lp

http://info.controlglobal.com/differential-pressure-lp

http://www.youtube.com/watch?v=-MQU0xgh6bA

http://www.youtube.com/watch?v=-MQU0xgh6bA

http://www.youtube.com/watch?v=siAMerrbpPU

http://www.youtube.com/watch?v=xfo9n_ly8sA

http://www.youtube.com/watch?v=xfo9n_ly8sA

http://encyclopedia.che.engin.umich.edu/Pages/ProcessParameters/LevelMeasurement/LevelMeasurement.ht



http://www.youtube.com/watch?v=0du-QU1Q0T4

http://www.youtube.com/watch?v=0du-QU1Q0T4

Documents

2017 STATE OF TECHNOLOGY LEVEL MEASUREMENT...TL ONTENTS 2017 State of technology: Level measurement 3 Liquid radar level moves up to 80 GHz 5 Radar level adds abilities 8 Density delivers