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THE DANFOSS JOURNAL. Published by Danfoss A/S, DK-6430 Nordborg, Denmark. Telephone: +45 7488 2222. Telefax: +45 7449 0949.E-mail: danfoss@danfoss.com. Telex: 50599 danfss dk. Visit us on the Internet: http://www.danfoss.com.Editor-in-Chief: Finn Märcher. Copyright: The publishers. Print: © Danfoss A/S 00.09.APH.FW.R.

AUTOMATIC CONTROLS DESIGN AND PRACTICE . 55TH YEAR NO. 3-2000 ISSN 0011-6076Also published in Danish, German, Spanish, Swedish, Dutch, French, Italian, Finnish, Russian, Polish, Czech, Chinese and Japanese.Reproduction of articles is usually permitted subject to acknowledgement. The editors accept no responsibility for possible errors in The Danfoss Journal.All trademarks in this material are the property of the respective companies. Danfoss and the Danfoss logotype are trademarks of Danfoss A/S.All rights reserved.Some Danfoss products mentioned in this publication may not be available in all countries.

Danfoss is a global company, created by theefforts of committed people respecting localvalues, mastering advanced technology andwith a high degree of environmental conscious-ness.

We are proud to present our products and ser-vices, which are for vital functions in our homes,at workplaces, in the industry and throughoutthe environment.

OXYgen-rich waterin the sea and infjords is a matter oflife and death – forfishes. With the newEVITA® OXY dissolved-oxygen sensor theoxygen content ofwater from waste-water treatmentplants is controlledbetter than ever.See article on page 8.

Water contamination inammonia refrigeration plantEvery day, Danfoss Industrial Refrigera-tion (DIR) has to advise customers allover the world whenever problems arisewith their industrial refrigeration plant.

Danfoss Constant Light™New outdoor lighting system fromDanfoss Lighting Controls.

Newly-developed pressuretransmitter for mobile hydraulicsDanfoss further strengthens its position asan innovative manufacturer of pressuretransmitters for hydraulic applications.

Shortening “time-to-market”With a dedicated bus communicationteam, Danfoss Instrumentation isdeeply involved in passing on tocustomers the new benefits availablefrom field bus communication.

Spring by the millionThe Danfoss Spring Factory has developedfrom being solely an in-house supplier forthe divisions of Danfoss into an indepen-dent business unit operating undernormal market conditions.

Nessie®®®®® water hydraulics– also suitable for mobile machinesA successful research project has shown that waterhydraulics can also be used with advantage asstandard equipment in forklift trucks.

Oxygen measurement revitalisedThe new EVITA® OXY dissolved-oxygensensor adds more user-friendly benefits tothe renowned Danfoss oxygen measure-ment technology for aeration tanks inwastewater treatment plants.

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Springs by the million

For almost three years the Danfoss SpringFactory has been part of the BurnerComponents Division. During the sameperiod the factory has developed frombeing solely an in-house supplier forthe divisions of Danfoss into an inde-pendent business unit operating undernormal market conditions.

During this period the number of custom-ers gained outside Danfoss accounts foralmost 20% of turnover, while at the sametime cooperation with internal Danfosscustomers has been maintained – primarilybecause of competitive prices, outstandingquality and an ability to keep to deliverypromises.

The spring factory has been developingand producing precision compressionsprings for the Danfoss quality productsthat are used in industrial applications allover the world for almost 40 years. Theexpertise and experience so gained isnow being offered to a broader circle ofnew customers – inside and outside theDanfoss Group.

The spring factory uses the latest pro-duction technology and its 60 expertemployees have taken up the challengeand today use their specialist knowledgein developing new types of springsfor customers in both existing andnew branches of industry. We offersprings made in a wide range ofmaterials and with many kindsof surface finish.

By Frank Rugbjerg Hansen,Sales RepresentativeCOMPONENTS FORBURNERS AND BOILERS

Today the spring factory regards itself asa cooperation partner for customers. Thismeans that we are only too pleased to helpdevelop and optimise springs for customerswhile keeping overall costs to a minimum.It also means that our designers shouldbe involved as early as possible in devel-opment work since process parametersand tolerances are often of great signifi-cance – both with regard to price and toensuring a design that best suits the sub-sequent assembly process.

In recent years the spring factory hasgained great success with a new totalsolution concept. The customer is offereda complete spring package exclusivelyfrom one supplier. The sizes of springs orvariants not included in the spring factory’sown range are obtained from other sup-pliers in our international network, butthe spring factory still guarantees both thequality of the entire package and punctualdelivery.

For more product information:Visit our homepage at www.danfoss.com/springs and ask for a brochure.Or contact Frank Rugbjerg Hansen,tel.: +45 7488 3656, or e-mail:springs-sale@danfoss.com

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Water contamination in ammonia refrigeration plant

Every day, Danfoss Industrial Refrigera-tion (DIR) has to use its knowledge andresources to help customers all over theworld solve problems with industrialrefrigeration plant. It is often the casethat the customer’s problem has nothingto do with our products or the way inwhich the plant is designed, but is theresult of completely different factors.

To help our customers save energy andminimise their service costs, we at DIRcollated some of our knowledge and ex-perience in a technical document whichwas presented to the 1998 annual confe-rence of The International Institute ofAmmonia Refrigeration (IIAR). This articleis an abstract of that document and itspresentation at the conference1).

The “vicious wet circle”The actual cause of many problems inindustrial ammonia refrigeration plants iswater contamination of the ammonia itself.Often, the only visible signs in the plantare just the result or a symptom of theproblem.

If the connection between cause andeffect in a refrigeration plant where theammonia refrigerant has been contami-nated by water is not known there is arisk of many resources being devoted to“curing” the symptoms rather than solvingthe real problem. We call this the “viciouswet circle”. (See fig. 1.)

The bottle testTo understand how large quantities ofwater enter an ammonia plant it is firstnecessary to look at the affinity that existsbetween water and ammonia. The easiestway to illustrate this phenomenon is byusing the so-called “bottle test”.If an empty bottle is turned upside down,filled with ammonia vapour and then takendown into water until the neck is immersed,water will begin to rise up in the bottle – atfirst slowly and then more quickly – untilthe bottle is almost full of water. The reasonis the affinity between water and ammonia;it is so great that the ammonia vapourdissolves in the water. The pressure in thebottle thereby falls and water is suckedup into it.The bottle test illustrates perfectly howwater can suddenly be sucked into anammonia refrigeration plant when therefrigerant is being evacuated, for exampleduring service work when it is normalpractice to blow the refrigerant out througha water-filled container. That is why theuse of a check valve in the drain line isalways recommended when ammonia isevacuated through water. The valve elim-inates the risk of water suddenly beingsucked into the plant (see fig. 2).

How and where does water come in?Water can enter a refrigerating plant inmany ways. Before starting up, there mayalready be water from pressure testing in

vessels, evaporators, condensers, etc., orwater condensate might appear becauseof temperature variations before the systemis charged with refrigerant. Such watercontamination can and should be avoidedpartly by drying out the system thoroughly,and partly by ensuring adequate vacuumin the system before the ammonia ischarged and the plant started.

When a plant is in operation, water canfind its way in when service work is beingcarried out, by accident (e.g. corrosion inchillers) or when on the low-pressure sideof the plant moist air is sucked in throughglands and gaskets that do not seal prop-erly. Water ingress in this way is especiallycommon if the normal suction pressureis lower than atmospheric pressure.

The air that enters the plant in this wayand which is blown out again on the high-pressure side (either manually or by anautomatic air purger) is completely drybecause it has yielded all the moisture itcontained to the ammonia and hence waterwill be accumulated. This is how wateraccumulates in the plant.

The aspect to be aware of here is that al-though automatic air purgers eliminate theproblem of air in the system, they do notsolve the problem of water accumulation.

The size of the problem can be illustratedwith the help of simple arithmetic:If 5 litres of air per minute is sucked intoa plant and allowed out again throughthe automatic air separator, and assum-ing an air temperature of 20°C [68°F]and air humidity of 80%, in the course of10 years the quantity of water dissolvedin the system ammonia will amount to363.5 litres.

Where is the water?Because of the great difference betweenthe vapour pressures of ammonia andwater, an ammonia refrigeration plantcan be regarded as a large distillery whereonly small amounts of water evaporatetogether with the ammonia. Water thusaccumulates in the low-pressure side, i.e.in liquid separators, intermediate coolers,etc. while, practically speaking, no waterappears in the high-pressure side.

The extraction of refrigerant in order tomeasure water content should thereforeonly be performed on the low-pressureside, while as much as possible of theammonia charge is on the high-pressureside of the plant. Such measurementswill reveal the largest percentage of watercontent.

By Per Skærbæk Nielsen,Product ManagerDANFOSS INDUSTRIALREFRIGERATION

Vapour from the system

Always use a check valve when evacuating through water

Fig. 2 The bottle testBottle test – shows the affinity between NH3 and H2O

Treating the symptoms, not the real problem

No investigation of water content

Increased service and operating costs

Capacity and energy consumption affected

Problems with valves and regulators

Corrosion

Fig. 1 Consequences of water contamination “Thevicious circle”

Incorrect service and maintenance procedures

Water penetrates into the system

Chemical reactions

Problems with oil and sludge, compressor affected

NH3Vapour

NH3Vapour

H20+NH3

H20

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How much water can actually be foundin a plant?In Denmark, Norway and Sweden, andwith the participation of the Danish Tech-nological Institute and other bodies, anextensive investigation into water contentwas conducted in 175 industrial ammoniarefrigeration plants. Of these, 25 containedmore than 3% water, 37 more than 2%and 77 more than 1%. In a few plants,water contents of 26%, 24% and 18.5%were found (see fig. 3).

In 65 of the plants examined a waterrectifier was installed to boil off the water.The quantity of boiled-off water was thenmeasured. In two of these plants, 250 litresof water were separated out and in oneplant 199 litres. On a further 10 plants, thefigures were between 100 and 150 litres(see fig. 4). In none of the plants wereservice personnel aware that there mightbe problems with water in the ammonia.

These measurements must be seen in thelight of the recommended water content inammonia refrigeration plant, i.e. max. 0.3%.

How can the water be removed?In industrial ammonia refrigeration plant,water is removed by distillation in a waterrectifier where the ammonia slowly evap-orates leaving the water behind in thevessel. When this process has beenrepeated many times, the residue in thecontainer is drained off. This normallyconsists of water with a content of about30-40% ammonia, depending on thepressure and temperature at the time ofemptying2).

What about filter driers?Danfoss has looked into the possibility ofproducing filter driers for ammonia refri-geration plant. The conclusion is thateven though it should be technically fea-sible to produce such a filter, it would bevery expensive and the amount of sepa-rated water very small in relation to thewater quantities that exist in ammoniarefrigeration plants (a few hundred gramsper filter).

In the case of small commercial ammoniarefrigeration plant with refrigerant chargesof less than about 4 kg, it is cheaper toreplace the whole charge several timesthan it is to install or replace a filter drier.Danfoss has also looked at other filters onthe market without finding any of themsuitable for ammonia refrigeration plant.

What happens to pressure and tempera-ture when water enters the plant?When water becomes mixed with theammonia, the thermodynamic propertiesof the mixture are different from those ofpure ammonia because changes occurin the relationship between the pressureof the respective saturated vapours andthe corresponding temperatures. At thesame pressure, an ammonia-water mix-ture has a higher evaporating temperaturethan pure ammonia. A refrigeration plantin which water has mixed with the ammo-nia must therefore operate with a lowerpressure in the evaporator to maintainthe same evaporating temperature than aplant with pure ammonia. This can haveserious consequences on plant capacityand operating economy.

A rule of thumb says, “at low evaporatingtemperatures the power consumption ofthe plant rises about 5% for each degreeCelsius the corresponding pressure dropson the suction side.” The plant capacityfalls markedly at the same time.

An example:At an absolute pressure of 3 bar [43.5 psia]the evaporating temperatures will be asfollows (see fig. 5):–9.23°C [15.39°F] with pure ammonia–6.69°C [19.96°F] with 10% water in theammonia–3.16°C [26.31°F] with 20% water in theammonia.Such a change in the evaporating tempera-ture because of water in the ammonia canhave a significant effect on the capacityand power consumption in, for example, achiller unit. When working with dry expan-sion on ammonia systems such changesin pressures and temperatures will be re-gistered as superheat by the thermostaticexpansion valve – without this being thecase. In the event of too high a “falsesuperheat” the valve will become unableto “control” the evaporator.

What happens “chemically” in the plant?Pure ammonia or, as it might be called,“dry” ammonia is not particularly chemi-cally reactive. In fact, if ammonia were freeof water and remained in this condition,copper or copper alloys such as brasscould be used in ammonia systems.

Fig. 4 Quantity of drained-off water per plant (1)

Litres

Dra

ined

-off

wat

er (1

)

EP temp. (-50;-31)ºCEP temp. (-31;5)ºC

Lowest evaporating temperature in refrigeration plant

175 refrigeration plants, totalMeasured values77: ≥≥≥≥≥ 1% water37: ≥≥≥≥≥ 2% water25: ≥≥≥≥≥ 3% water

Fig. 3 Water content given at evaporating temperature

Intermediate cooler (-50; -31) ºCSeparator or evaporator (-50; -31) ºCSeparator or evaporator -31 ºC

Wat

er/w

eigh

t per

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age

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Conversely, aqueous or “wet” ammonia isvery chemically reactive and very aggres-sive towards copper, copper alloys, zinc,etc. “Wet” ammonia is highly corrosiveand can lead to galvanic corrosion of thevalves, which in turn might result in regula-tion problems. This corrosive environmenttogether with vibration and/or pulsation canalso give rise to the phenomenon knownas “fretting corrosion” where surface metalfatigue, wear and corrosion becomes in-tensified by the presence of the other two.Under these conditions, mechanical reg-ulators and valves can either seize upcompletely or malfunction because of in-creased friction (see fig. 6).

What about the oil?Ammonia containing water and oxygenalso reacts with the oil in the compressorand creates reaction products. Some ofthese are organic acids that react withthe ammonia and form complex nitrogencompounds (e.g. sludge, salt and soapproducts) all of which are highly injuriousto the plant.

Characteristic of the nitrogen compoundsis that:– they are partially soluble in ammonia

(the ammonia becomes coloured),– they do not dissolve in oil,– they are able to pass through the oil

separator together with the ammonia,– they create sludge in the compressor

and throughout the whole system(valves, regulators, evaporators),

– they act as catalysts which acceleratethe on-going process by creating moredamaging nitrogen compounds.

Orifice wear in an ammonia plant?It is well known that the orifices can besubjected to wear because of the erosionand cavitation that occur in the orificewhere expansion takes place. Erosion iscaused by the flowing medium, which atcertain points can reach a velocity almostthe same as that of sound. Cavitationarises because small bubbles in theammonia implode (collapse).

Wear in orifice elements such as floats andexpansion valves becomes greater whenthe ammonia contains water. The watercreates corrosion in the orifice, i.e. it addscorrosion to the erosion and cavitationalready taking place. Furthermore, waterin the ammonia might intensify the cavi-tation affecting the orifice (even thoughthis has not been scientifically proved).Wear from erosion is also intensified bythe larger amounts of rust and sludgeparticles that circulate in the system.

ConclusionIt can be concluded that ammonia refri-geration plants often contain more thanthe maximum recommended 0.3% water.This can be because automatic air purgers“hide” leakage and allied problems whichallow water to accumulate in the system.Another cause is that personnel who ser-vice such plants are not always very wellacquainted with water-related problems.

It is thus a very good idea to make theinspection of system water content a partof normal service and maintenance proce-dures. Finally, the installation of a waterrectifier can be an attractive investmentin terms of operating economy.

The “good dry circle”Now let us look at the “good dry circle”where the real problem is cured ratherthan just the symptoms (see fig. 7).

The initial step is to follow the correctprocedure in starting up and servicingthe plant. The better these instructionsare observed the fewer the problems withoil and sludge become, and the smallerbecomes the risk of corrosion. Problemswith mechanical valves and regulatorswill thus be fewer.

Making sure that the plant runs withminimum water content means lowerservice and operating costs, withoutnegatively affecting capacity and powerconsumption.

For further information, please contactPer Skærbæk Nielsen, tel.: +45 87389641, fax: +45 8628 0801, or e-mail:psn.dkacd@danfoss.com

The real problem is solved and not just the symptoms

Investigation of water content. Use of water rectifierunits

Reduced service and operating costs

Capacity and energy consumption not affected

Fewer problems with valves and regulators

Minimum risk of corrosion

Fig. 7

Advantages of keeping systems dry – “The good circle”

Correct service and maintenance procedures

Minimum water penetration

Minimum number of chemical reactions

Fewer problems with oil and sludge. Longer serviceintervals

Fig. 6Water-related problems on valves and mechanicalregulators

Rust and sludge“Fretting” corrosionValves, filters can become blocked or seize up

Vibration/pulsationFatigue in asperitiesAsperities break offLoose particles on surface + corrosionParticles grow in sizeIncreased frictionIncreased wearValves and regulators seize up

2Fe + 02 →→→→→ Fe0, black3Fe0 + 1/2 02 →→→→→ Fe304, blue/black2Fe0 + 1/2 02 →→→→→ 3Fe2 03 , red/brown →→→→→ wearFe203 + H20 →→→→→ 2Fe00H, red/brown →→→→→ rust

Many small movements

1) A copy of the DIR (Danfoss Industrial Refrigeration)technical document “Effects of Water Contaminationin Ammonia Refrigeration Systems” can be obtainedfrom the author of this article.

2) For a more detailed description of how water contentis measured and how water is boiled off in ammoniasystems refer to the IIAR (The International Instituteof Refrigeration) technical bulletin no. 108.

0.05 NA NA NA NA -50 0.254 0.326 0.373 0.4080.1 NA NA NA NA -48 0.285 0.366 0.420 0.4490.2 NA NA NA NA -46 0.321 0.411 0.471 0.5150.3 -47.15 NA NA NA -44 0.360 0.460 0.527 0.5760.4 -42.10 -46.48 -48.82 NA -42 0.402 0.514 0.588 0.6440.5 -38.00 -42.51 -44.93 46.52 -40 0.449 0.573 0.655 0.7171.0 -24.07 -28.96 -31.71 -3359 -38 0.500 0.637 0.797 0.7972.0 -7.71 -13.62 -16.70 -18.85 -36 0.556 0.708 0.808 0.8853.0 -2.51 -3.16 -6.69 -9.23 -34 0.617 0.784 0.895 0.9804.0 -10.32 4.45 -0.79 -1.88 -32 0.679 0.986 0.986 1.08

Fig. 5: Thermodynamic properties NH3 + H2O

SaturationpressureBar

Saturation temperature, °C if

NH3 70% 80% 90% 100%N20 30% 10% 10%

SaturationpressureBar

Saturation temperature, °C if

NH3 70% 80% 90% 100%N20 30% 10% 10%

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Electrically driven forklifttruck with Nessie® water hydraulics.

Nessie® water hydraulics – also suitablefor mobile machines

A successful research project has shownthat water hydraulics may also be usedwith advantage as standard equipmentin forklift trucks.

Water hydraulics is no longer restrictedto stationary applications; good use canalso be made of water hydraulics and itsmany advantages in mobile machines.Among the characteristics offered by waterhydraulics are excellent functionality andreliability, low purchase price, energy-saving design and, last but not least, avery environment-friendly pressure medium.

This is the brief conclusion from the Eurekaresearch project “Water-hydraulic liftingsystems with variable speed” in whichDanfoss, in cooperation with the “Institutfür Fluidtechnik” at the Dresden Universityof Technology, Germany, converted anordinary electrically driven forklift truck foroperation with a water-hydraulic liftingand tilting system.

Even in the preliminary studies it couldbe documented that solely from the pointof view of function, water-hydraulic systemslend themselves incredibly well to mobilemachines, even though units such as fork-lift trucks do impose high demands onwater hydraulics. Nevertheless, successfuldevelopment work on the new forklift truckhas been carried out in different areasand users will be able to take advantageof both the technical and ergonomicprogress made.

No grounds for prejudiceThe positive results of the project go a longway in dispelling many of the prejudicesoften expressed in connection with water-hydraulic systems in mobile machines.A few of the usual prejudices are givenbelow together with counter-arguments:– Prohibitive cost of hydraulic compo-

nents such as pumps and valves, moreexpensive actuators (cylinders of specialsteel). Against this are the advantagesof design changes involving blockdesign, the module principle, coatedcylinders or plastic cylinders, etc.

– Another prejudice is that the temperaturewater hydraulics is able to withstand– whether the working temperature orambient temperature – is limited. Butindoor temperatures can nearly alwaysbe held between +3 and +50°C; a rangein which water hydraulics functionsvery reliably. For outdoor applicationsit is possible to use anti-frost additivesin the water, e.g. environment-friendlyglycols. Furthermore, through activecooling, high temperatures can be re-duced in water-hydraulic systems mucheasier than with oil hydraulics, in thatwater has much better heat conductivity.

– Another advantage of water hydraulicsis often overlooked: The viscosity ofwater changes very little within theworking temperature range. Thus, waterflow conditions remain constant andthere is none of the start sluggishnessso often experienced with mineral oil,which means higher energy consump-tion and extra wear.

Design details from the research projectThe hydraulic changeover function in theforklift truck has been optimised by usinga Danfoss CAN bus serial communicationinterface, the necessary pressure beinggenerated by a Nessie® axial piston pump.

The direction of travel of lifting and tiltingcylinders is controlled by Nessie type 2/2-way directional valves, while the speedis controlled by Nessie proportional flowregulating valves bridge-coupled withcheck valves. Pressureless circulation isensured by check valves that protect thepump, and a bypass valve.

Lifting and tilting speeds depend on themovements of the joystick which, in turn,determine pump output. Matching pumpdelivery to demand can therefore give aconsiderable reduction in the amount ofenergy used by forklift trucks, whichnormally consume a great deal of energy.

The control block – compact anduniversally applicableThe project also included the developmentof a control block consisting of standardvalve components from the Nessie waterhydraulics range. The basic requirementin this development was a compact unit,the dimensions of which would allow in-stallation in the restricted space availablein forklift trucks.

The system is built up of modules andcan thus be extended as required. Thecontrol is divided into individual blockswhich as far as possible are of universaldesign and can be combined to suit theapplication.

For further information, please contact:Torben G. Pedersen, tel.: +45 74885272, fax: +45 7445 3831, or e-mail:tgp@danfoss.com

At the moment, Nessie water hydrauliccomponents are distributed in WesternEurope and the USA.

Nessie® is a registered trademark of Danfoss A/S.

By Rudolf Fritzsche,Product ManagerDanfoss Antiebs- undRegeltechnik GmbH,GermanyWATER HYDRAULICS

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Oxygen measurement revitalised

The new EVITA® OXY dissolved-oXYgensensor adds more user-friendly benefits tothe renowned Danfoss oXYgen measure-ment technology for aeration tanks inwastewater treatment plants.

On-line oxygen measurement for the con-trol of processes in wastewater treatmentplants is rapidly gaining ground – thanksnot least to the fact that it paves the wayfor savings as high as 25-65 percent ofthe energy consumption.

As the world’s leading supplier of oxygenmeters, Danfoss has fuelled this develop-ment with EVITA® OXY measurement tech-nology, originally introduced more than20 years ago. And with the recent launch-ing of a radically improved version – theEVITA OXY dissolved-oxygen sensor – arange of new user-friendly features is with-in reach where installation, maintenance,reliability and long-term accuracy areconcerned.

Fast installationAs everyone in this industry knows, in-stalling oxygen meters in aeration tankscan be very tiresome. Most makes requirea supply of water and compressed air forcleaning the sensor – a costly arrangement,especially in major wastewater treatmentplants. In addition, cabling is usually com-plicated, and in many cases there is arisk of damage to the meter because ofincorrect installation.

The EVITA OXY dissolved-oxygen sensorovercomes these obstacles by virtue of aninstallation procedure that can be com-pared to putting a plug in a socket. Thesensor comes with two wires, requiringonly the connection of power cable andsignal cable. No technical skills are re-quired; the operation can be performedwithout a manual, and no damage canbe done to the sensor during installation.

Easy maintenanceTime-consuming maintenance often standsin the way of the profitable use of oxygenmeasurement. With the EVITA OXY sensor,Danfoss has overcome this barrier byoffering a sensor that needs minimummaintenance. In addition, subsequenthandling is operator-independent.

This user-friendliness is manifested by anumber of design details. Among them are:– Calibration only twice a year.– Automatic calibration: Calibration takes

less than five minutes by simply tiltingthe sensor, i.e. a tilt switch, TILTCAL®,automatically initiates the calibrationroutine.

– Self-cleaning thanks to a patentedsensor design with one float and fourfins that increase water velocity aroundit by 125 percent – enough to renderthe use of compressed air, fresh water,grindstones or chemicals superfluous.

– Cleaning confined to three times yearlyand then only a cloth to wipe thesensor is necessary.

– Simple replacement of the sensor everytwo or three years has taken the place ofrenovation. The operation is performedquickly, with no mistakes possible: Thecollar holding the sensor in place is un-screwed and a new sensor is inserted.

By Helle Obeling,Product SponsorDANFOSS ANALYTICAL

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Enhanced reliabilityThe fact that the EVITA OXY dissolved-oxygen sensor offers replacement of thesensor instead of renovation not onlymeans easy maintenance. It also ensuresthe accuracy of measured values andthus considerably enhances the reliabilityof the method.

Sensor replacement instead of renovationmeans that precision is not affected bythe risky handling of O-rings, membranes,cleaning liquids and other variables thatinfluence accuracy.

Another detail that increases reliability isthe sensor construction without O-rings.Instead, the pre-stressed membrane isbonded direct onto the sensor, preventingany water percolation.

Furthermore, the sensor is provided withan alarm that is triggered by membraneleakage. And the electronics are self-diagnostic.

Accuracy in the long runNaturally, accuracy is a matter of concernto all operators of wastewater treatmentplants. However, the crux of the matteris: How long will the accuracy achievedduring installation last?

The EVITA OXY sensor answers this ques-tion more satisfactorily than any otheroxygen meters have been able to so far.The design ensures unerring measure-ment and accurate results for years afterthe sensor has been installed.

An unimpaired membrane is particularlyimportant when it comes to the accuracyof oxygen measurement. ConsequentlyDanfoss has focused strongly on thisaspect to ensure long-term accuracy.

An extremely accurate Pt 1000 tempera-ture sensor (>0.01ºC) ensures correctcompensation of temperature-depend-ent membrane permeability. In this way,the constant accuracy of measuredvalues is ensured. As an extra benefit,contamination of the electrolyte isprevented.

Combined with the advantages alreadymentioned: elimination of renovation,automatic leakage detection, and the self-cleaning feature, this membrane designgives years of unfailing process optimisationin the aeration tanks of all wastewatertreatment plant.

For more information about the EVITA® OXY

dissolved-oxygen sensor, please contactHelle Obeling on +45 7442 1056-207, ore-mail: danfoss.analytical@danfoss.com

EVITA® is a registered trademark of Danfoss A/S.

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A new outdoor lighting system fromDanfoss Lighting Controls: Danfoss hasintroduced a new lighting system whichin addition to giving a much higher qualityof illumination in outdoor applicationsalso means significant energy savings.

The lighting system has been speciallydeveloped for advertising and traffic signs.The system makes it possible to dimen-sion the light intensity in a sign to ensureconstant optimum colour reproductionirrespective of the ambient temperature,the supply voltage, and tube deterioration.

Light quality and energy consumptionEveryone with experience of fluorescenttubes in areas with varying temperatureshas met the problem: The great differencein light output in relation to the ambienttemperature and tube deterioration. Innormal systems it is therefore necessaryto dimension the sign so that acceptableillumination is ensured even at very lowtemperatures. This means that in certainperiods the light intensity is far higher thandesired, therefore the amount of energyconsumed by the sign is also too high.

Our experience with illuminated signsshows that the desired degree of illumi-nation lies at a level equivalent to thatobtained when the ambient temperatureis around 0°C [32°F]. The graph belowshows the light output from Danfoss Con-stant Light™ with thermotubes com-pared with conventional lighting systems.

As can be seen, the yellow hatched areaexpresses surplus illumination and wastedenergy because the actual requirementis lower light intensity. The green hatchedarea expresses poor illumination qualitywhich could be avoided with DanfossConstant Light, without increasing theelectricity bill.

Measurements taken in cooperation witha sign manufacturer and the KøbenhavnsBelysningsvæsen (Copenhagen Energy)have shown that it is possible to save upto 58% in energy consumption and atthe same time achieve a better degree ofillumination. A résumé of the report fromKøbenhavns Belysningsvæsen can beobtained from Danfoss Lighting Controls.

Corporate imageA large part of the marketing work carriedout by modern companies is aimed atdifferentiating each company from itscompetitors. Here, the projection of acompany’s corporate image is an importanttask and illuminated signs have an essen-tial role to play in such communication.

Danfoss Constant Light now makes itpossible to manufacture signs of optimumcolour, design and illumination quality.The system also ensures that this highquality is maintained at all temperaturesthroughout the entire life of the sign.

Signs incorporating Danfoss Constant Lightare also very attractive from the point ofview of economy. The large energy savingsthey give mean much lower operatingcosts.

Another aspect is that the energy savingsachieved lighten the burden on the envi-ronment. In addition, there is a possibilityof meeting the increasing demand for areduction in “light pollution” which in manyplaces is given high priority.

Design freedomThe manufacturer now has the possibilityof designing signs that meet customerwishes without compromise. DanfossConstant Light is intended for signs thatmeet severe demands on lighting stabilityand thus colour reproduction, whateverthe ambient temperature.

Not only can the desired light intensityand colour reproduction be achieved andmaintained, but there is much greaterflexibility as regards the number of tubesand their placing in the sign.

And as already mentioned, Danfoss Con-stant Light cuts down the amount ofenergy consumed by illuminated signs.

Illumination profileDanfoss Constant Light can of course beconnected to on/off control, dimmingrelays and similar equipment.

The big advantage here is that the desiredillumination profile can be set for 24 hoursso that in certain periods, dusk for ex-ample, dimming is suppressed to give asharper contrast with the surroundings.When darkness falls, the system is acti-vated automatically and more energy issaved.

With such an illumination profile there ismuch to be saved on the electricity bill,the communication value of the sign isimproved, and a more attractive milieu iscreated.

System build-upThe system is very simple in build-upand can therefore easily be installed inexisting signs to give the same advantages.

By Finn Nicolaisen,Marketing ManagerDANFOSS LIGHTINGCONTROLS

Light output from an illuminated sign with Danfoss Constant Light™ compared with a conventional lighting system.

(Reference point = 0°C)

Temperature ºC

Conventional lighting system

Danfoss Constant Light

Ligh

t out

put (

lux)

Danfoss Constant Light™

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Danfoss Constant Light consists of one ormore Danfoss EBH 2000 high-frequencyelectronic ballasts and a controller, EBC1001, that is able to control several hun-dred EBHs and associated equipment.

The EBC 1001 controller can be positionedso that its built-in sensor registers on oneof the fluorescent tubes in the sign andensures that the light intensity from thissource is held constant at a certain level.

Both the Danfoss EBH 2000 high-frequen-cy ballasts and the EBC 1001 controllerare heavy-duty models. The standardversions are protected against moisture,corrosion and vibration, and can thereforebe used outdoors. These components arealso available in an IP 65 version for parti-cularly demanding applications. DanfossConstant Light will ignite fluorescent tubesin ambient temperatures right down to–35°C [-31°F] and, to take the oppositecase, right up to +75°C [167°F].

Danfoss Constant Light gives “the rightillumination”, to the satisfaction of:– those who see the sign as part of the

corporate image,– those who just see the sign,– those who maintain the sign,– those who have to pay the electricity bill,– and not least the environment!

For further information on DanfossConstant Light™, please contactFinn Nicolaisen, tel.: +45 7488 4745,fax: +45 7488 6998, or e-mail:lighting@danfoss.com

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Newly-developed pressure transmitterfor mobile hydraulics

With the introduction of the new MBS3250 high-temperature version in theseries of heavy-duty pressure transmitters,Danfoss further strengthens its positionas an innovative manufacturer of pressuretransmitters for hydraulic applications.

BackgroundFor many years Danfoss pressure trans-mitters have been used for demandingapplications in hydraulic systems in manyindustries (e.g. wind turbine gears, ships’winches, presses). In 1998, on the basisof experience gained, Danfoss launcheda series of heavy-duty pressure transmit-ters intended especially for applicationswhere high pressure peaks, liquid hammerand/or cavitation occur. Close cooperationwith customers within agriculture, forestry,mining, building and construction, and inparticular Danfoss Fluid Power (now Sauer-Danfoss A/S) led to product adaptation inorder to meet the special requirementsof such industries. In addition to liquidhammer, there are ever-increasing oiltemperatures, large variations in ambienttemperatures, and very strict EMC require-ments to meet, all factors which have hada decisive influence on the design of thenew pressure transmitters.

A new solution to an old problem– liquid hammerApplications where strong pressure surgesor liquid hammer occur are nothing new– on the contrary*. But as described pre-viously, the problem cannot be solvedmerely by concentrating on the pressuresurge itself, it is very important to look atthe situation ahead of the pressure surge.This phenomenon is most often seen onthe outlet side of a valve or pump: rapidload variations resulting from the move-ments of a vehicle on open terrain cancreate gas pockets or cavitation in frontof the pressure transmitter diaphragm.This occurs when the pressure becomeslower than the vapour pressure of theliquid. Gas pockets or cavitation can tearthe liquid from the pressure transmitterdiaphragm.

When the liquid column is sucked back it“hammers” back against the diaphragmwith a force as if from a metal bar.The solution to the problem is simple andeffective: The incorporation of a dampingnozzle (pulse snubber) in the pressuretransmitter to prevent dangerous cavitationat the diaphragm (see fig. 1).

Unlike other sensors, the piezo-resistivesilicon sensor needs no protection againstpressure peaks, in that the pressure safetyfactor is typically six times (max. 1500 bar)the measuring range. Therefore the nozzlediameter can be so large that it does notnoticeably increase the total (mechanicaland electronic) time constant of the pres-sure transmitter for normal viscosities(τ < 4 ms at 100 cSt.)

Increasing oil temperaturesIn contrast to hydraulic systems in industrywhere, typically, large quantities of oil areavailable for the system, mobile applica-tions have to operate with relatively smallquantities. This imposes severe demandson the hydraulic oil cooling system whichin practice has to cope with oil at workingtemperatures of more than 100°C [212°F],in some cases even up to 125°C [257°F].The MBS 3250 series has been speciallydeveloped to meet these severe demandsand will complete the existing range ofMBS 3050 pressure transmitters, espe-cially for applications where workingtemperatures exceed 85°C [185°F].

The big challenge has been to developa pressure sensor with sufficiently goodlong-term stability at 125°C [257°F], sothat the transmitter would be capable ofreliably measuring pressure year afteryear, without recalibration or adjustment.Since pressure transmitters in such appli-cations are often installed encapsulated,the temperature within the encapsulationcan also reach 90-125°C. The wholetransmitter (not just the sensor) musttherefore be able to withstand high work-ing temperatures.

Extreme ambient temperatures-40°C to 125°C [40°F to 257°F]All components in the hydraulic system ofvehicles must be capable of withstandingextreme environments. If the enclosure isnot absolutely tight, moisture will find itsway in: the pressure in the encapsulationwill change as a function of the temperature(according to Avogadro’s law, ((P x V)/T =Constant). If V (volume) is assumed to beconstant, the air pressure in the encap-sulation will change with the temperature).Pressure changes normally produce a“pumping effect” (during pressure equa-lisation) which in under-pressure periodssucks moisture into the encapsulation –often with catastrophic consequences forelectronic products. The pressure trans-mitters in the heavy-duty series are pro-tected against moisture using elasticsilicone potting compounds. The electricalconnector end of the transmitter incorpo-rates a new, patented seal which givesoptimum resistance to moisture ingres-sion, even via pumping. Where possible,the use of gaskets and O-rings insidethe transmitter has been avoided. Thesensor is fully welded and contains nointernal seals.

Søren LiljenbergBusiness Area ManagerINDUSTRIAL CONTROLS

Fig. 1Pulse snubber

* The Danfoss Journal 1-1998:The pressure transmitter - a small detail withgreat influence, by Ole Friis Knudsen

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Electrical connection/plugExperience from the last two years inmarketing the heavy-duty series is mostclearly reflected in the electrical connec-tion. In many applications, ingress ofmoisture and dust, as well as vibrationhave presented almost insoluble problemsfor years. There are many different typesof connections on the market, especiallybecause the number of standardised con-nections is limited. But we see a tendencytowards the use of plugs from the automo-tive industry and the MBS range includesconnections with an ingress protection ofup to IP 69K (steam-jet-proof).

EMCAll pressure transmitters from Danfosscarry the CE mark and therefore follow EUdirectives on EMC (EN 50081-1/2 andEN 50082-1/2). Our many years of expe-rience in this area, and the fact that thecompany has its own EMC test facilities,have been decisive in developing the heavy-duty pressure transmitters. In additionto the EU standards mentioned, severalbranch-related EMC standards have ap-peared, among them ISO 13766 “Earth-moving machinery – EMC”, DIN 40389(EMV in Straßenfahrzeugen) and EN ISO14982 “Agricultural and forestry machines– EMC – Test methods ..”, which lay downmany more stringent requirements onelectronic components, especially thosethat are part of safety or steering systems(brakes, speed control, steering). Depend-ing on the output signal and plug confi-guration, the new heavy-duty transmittershave already been tested for noiseimmunity up to 100 V/m.

ApplicationsControl and monitoring of hydraulicpressureThrough the years several companies haveused Danfoss MBS 3050/4050 pressuretransmitters in connection with the controlof rotation, applied force and system pres-sure in mining drills, an application whichimposes severe demands on transmitterreliability, mechanical robustness, andthe ability to withstand high pressurepeaks. Up to nine transmitters on eachdrilling rig form part of a computerisedcontrol system that has made the drillingprocess far less operator-dependent.

SafetyIn recent years the EU has introducedlegislation to increase crane and forklifttruck safety. One requirement is that itmust not, under any conditions, be possi-ble for cranes/forklift trucks to topplebecause of overload. A number of com-panies have therefore incorporated pres-sure measurement in their equipment tomonitor load. Where cranes are concerned,pressure measurement is combined withthe measurement of boom angle, i.e. theapplied moment is calculated – the distancefrom the axis of the crane to the middleof the load multiplied by the weight of theload.

PerspectivesThroughout the mobile hydraulics industry,the scene is one of rapid developmentwhere electronic sensors and controls playa decisive role. Accelerating demands inrelation to efficiency, safety and the envi-ronment increase the need for machineautomation.

An obvious example is agriculture wheremuch discussion is devoted to “PrecisionFarming” – a new development that evennow is changing the way in which wecultivate and harvest our fields.

Among the processes used here is thecontinuous measurement of harvest yield.This makes it possible to prepare a profilethat can be used the next year to deter-mine the quantity and distribution of fer-tiliser. Again this imposes severe demandson machine automation and the continu-ous measurement of, for example,– harvest yield– dosing of fertiliser– positioning, using GPS (Global Position

System) and differential GPS.

The same tendency can be seen in manyother industries and as a producer ofhydraulic components Danfoss is deeplyinvolved in such developments. In recentyears the company has been devotingmore and more attention to electricallycontrolled hydraulic systems and today isable to offer complete solutions (systemintegration). This knowledge of systemsand the many years of experience Danfosshas gained as a manufacturer of pressuretransmitters comprise the basis on whichthe new range of transmitters has beendeveloped.

For further information, please contactSøren Liljenberg, tel.: +45 7488 5899,fax: +45 7488 5757, or e-mail:sliljenberg@danfoss.com

Fig. 3 Truck/crane weighing

Fig. 2 Product range

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– A Profibus PA add-on module waslaunched earlier this year, followingsuccessful field trials in England andGermany. This module conforms tothe Profibus flow transmitter »profile«which covers both magnetic and massflow transmitters. Some extra system-specific functions included in this releaseare ‘Batch control’ and ‘USM-II specificerror and diagnostics messages’. Moreadvanced system-specific features maybe added based on customer feedback.

– In the pipeline:Profibus DP: This version of Profibusis optimised for speed and is typicallyused in systems where intrinsic safetyand loop powering of instruments arenot required. It is especially useful forbus interfacing flow transmitters withother Danfoss products such as VLT®

frequency converters.DeviceNet: This popular and efficientbus system is fast becoming a nichearea for Danfoss Instrumentation, whoat present is one of the few suppliersof magnetic and coriolis mass flow-meters with direct DeviceNet support.

Functionality easily enhancedAlthough the standard Profibus flow trans-mitter profile is fairly comprehensive, theDanfoss flow transmitters have manymore features in addition to those alreadymentioned. Nevertheless, our modulehas been designed to make it relativelyeasy to add more Danfoss system-specificfunctionality if required. The decisionwhether to add anything extra is mainlydetermined by feedback from field trialsand the market feedback following fullrelease.

The basis for this approach is in keepingwith the overall objective of the bus com-munication team: to provide full protocolcompliance – no more no less – for eachcustomer as fast as possible. Not every-one needs (or wants) a solution with allthe »bells and whistles«. However, every-body wants new benefits fast!

In case customers come up with specialrequirements, this approach does not letanyone down. Our USM-II platform andour organisation are geared to developingtailored functionality in close collaborationwith users. This flexibility is unrivalled inthe flowmeter industry.

– Investment protection: Change of bussystem does not require changing thesignal converters – an extremely cost-saving benefit in these times of frequentorganisational changes which often leadto different project management strate-gies, e.g. a company merger mightchange bus selection strategiesdramatically.

– The modules add – they do not substi-tute. Extra I/O terminals are reservedfor the add-on modules to ensure thatstandard I/Os, including the 4-20 mAoutput, are still available if required.Thus no functionality is lost when addinga module to the signal converter.

– Existing plant configuration and wiringcan be retained in parallel with addingnew bus functionality.Reduced inventory:

– One signal converter for either analogor field bus requirements.

– The same modules are used for bothMAGFLO and MASSFLO meters

– The module can be plugged into a newsignal converter in case of damage tothe latter.

Concept on the moveAs the word ‘modular’ suggests, theUSM-II concept is dynamic – constantlyintroducing the latest conquests in buscommunication technology. And this isprecisely where the Danfoss bus commu-nication team gets into the picture. Ourprimary goal is to initiate the developmentof add-on functionality to meet the require-ments of the market by offering standardand customised fieldbus solutions andgetting them to the market as fast aspossible.

The current state of our efforts can besummed up as follows:– A HART® add-on module was intro-

duced about a year ago. This modulehas complete generic support for theHART protocol as well as a comprehen-sive system-specific command set.System drivers have been developedand registered with the HART Communi-cation Foundation. We are constantlyendeavouring to develop other systemdrivers for major HART master systemsto further enhance the applicabilityand user-friendliness of the module.Its flexibility already means that mostfeatures and functions of the trans-mitter are available in Windows-basedapplications as well as in hand-heldcommunicators.

With a dedicated bus communicationteam, Danfoss Instrumentation is deeplyinvolved in passing on to customers thenew benefits available from field buscommunication.

The bus communication field is complex,fast moving and raises a host of questions.To mention just a few: Which conceptshould I choose? How is it implemented?What are the total costs?

This situation calls for clear signals on thepart of suppliers of instrumentation to thewater business, industries and districtheating. To improve its responsiveness tothis vital customer requirement, Danfosshas formed a bus communication teamwith a determined commitment to monitormarket developments and utilise theknowledge obtained for further productdevelopment.

The endeavours of the team are basedon solid ground: The recently introduced,modular and flexible USM-II technologyplatform for MAGFLO® electromagneticflowmeters and MASSFLO® mass flow-meters. USM-II is the only flow transmit-ter concept on the market that supportstrue plug-and-play functionality. Amongits many features the following deservespecial mention:– Unsure which bus system to implement?

With USM-II you can take the signalconverter now, and add or change thebus later.

– Easy installation: Add-on modules areplugged into the signal converter with-out the use of tools.

– No additional programming: When thesignal converter is powered up, the mo-dule is auto-detected by the converterand adds a new menu item in thelocal keypad/display (if one is fitted).

By Wayne Gray-Garney,Product Manager– Bus CommunicationsINSTRUMENTATION

Shortening time-to-market

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German automotive manufacturers areamong MASSFLO OEM customers whohave derived specific advantage from ourflexible and modular USM-II design. Theirrequirements led us to develop a custom-ised CAN bus module for a time-criticalbatch application using MASSFLO meters.

By focusing our attention evenly on devel-oping the standard fieldbus profiles as wellas customised solutions for individual re-quirements, we consider both the wide-spread fast-to-market interest and theneed for individual and more time-savingsolutions.

Successful installation ensuredAnother focal point of the Danfoss buscommunication team is the compatibilityof our products with the reality they areconfronted with. In other words, we recog-nise the need to understand how our sys-tems present themselves on major bussystems, masters or hosts.

In consequence, we frequently work outstep-by-step instructions to help custom-ers cope with typical configuration andsetup issues. By providing the necessaryknowledge we see to it that our productsare ‘escorted home’ – all the way tosuccessful installation in the applicationconcerned.

For further information, please contact:Wayne Gray-Garney, tel: +45 7488 2651,fax: +45 7488 3414, or e-mail:wayne@danfoss.com

MAGFLO® and MASSFLO® are registeredtrademarks of Danfoss A/S.

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The Danfoss product range comprises refrigeration and air conditioning controls, components for burners and boilers, comfort controls, industrialcontrols, mobile hydraulics, water hydraulics, compressors for refrigerators and freezers, thermostats for refrigerators and freezers, heating andventilating controls, electrical drives and controls, instrumentation, compressors for air conditioning and refrigeration and water valves.

DJ.00.03.02

Pump stations and valves

The complete pump range

Gearwheel pumpsup to 6,000 l/h