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Application Bulletin

DeionizeD water

Water Quality InstrumentationAccuracy Reliability Simplicity

Years ago, high purity water was used only in limitedapplications. Today, deionized (Dl) water has become an

essential ingredient in hundreds of applications including:medical, laboratory, pharmaceutical, cosmetics, electronicsmanufacturing, food processing, plating, countless industrialprocesses, and even the nal rinse at the local car wash.

THE DEIONIZATION PROCESS

The vast majority of dissolved impurities in modern watersupplies are ions such as calcium, sodium, chlorides, etc. Thedeionization process removes ions from water via ion exchange.Positively charged ions (cations) and negatively charged ions

(anions) are exchanged for hydrogen (H+) and hydroxyl (OH-)ions, respectively, due to the resin's greater afnity for otherions. The ion exchange process occurs on the binding sites of

the resin beads. Once depleted of exchange capacity, the resinbed is regenerated with concentrated acid and caustic whichstrips away accumulated ions through physical displacement,leaving hydrogen or hydroxyl ions in their place.

DEIONIZER TYPES

Deionizers exist in four basic forms: disposable cartridges,portable exchange tanks, automatic units, and continuousunits. A two-bed system employs separate cation and anionresin beds. Mixed-bed deionizers utilize both resins in the samevessel. The highest quality water is produced by mixed-beddeionizers, while two-bed deionizers have a larger capacity.Continuous deionizers, mainly used in labs for polishing, donot require regeneration.

TESTING Dl WATER QUALITY

Water quality from deionizers varies with the type of resins used,feed water quality, ow, efciency of regeneration, remainingcapacity, etc. Because of these variables, it is critical in manyDl water applications to know the precise quality. Resistivity/conductivity is the most convenient method for testing Dl waterquality. Deionized pure water is a poor electrical conductor,having a resistivity of 18.2 million ohm-cm (18.2 megohm) andconductivity of 0.055 microsiemens. It is the amount of ionizedsubstances (or salts) dissolved in the water which determineswater's ability to conduct electricity. Therefore, resistivity andits inverse, conductivity, are good general purpose quality

parameters.

Because temperature dramatically affects the conductivity ofwater, conductivity measurements are internationally referencedto 25C to allow for comparisons of different samples. Withtypical water supplies, temperature changes the conductivityan average of 2%/C, which is relatively easy to compensate.Deionized water, however, is much more challenging toaccurately measure since temperature effects can approach10%/C! Accurate automatic temperature compensation,therefore, is the "heart' of any respectable instrument.

RECOMMENDED INSTRUMENTATION

Portable instruments are typically used to measure Dl watequality at points of use, pinpoint problems in a Dl system conrmmonitor readings, and test the feed water to the system. Thehandheld Myron L Company instruments have been the rschoice of Dl water professionals for many years. For two-bedDl systems, there are several usable models with displays ineither microsiemens or ppm (parts per million) of total dissolvedsolids. The most versatile instruments for Dl water is the 4Por 6PFCE Ultrameter II, which can measure both ultrapuremixed-bed quality water and unpuried water. It should be notedthat once Dl water leaves the piping, its resistivity will dropbecause the water absorbs dissolved carbon dioxide from theair. Measuring of ultrapure water with a hand-held instrumenrequires not only the right instrument, but the right technique

to obtain accurate, repeatable readings. Myron L Companyinstruments offer the accuracy and precision necessary foultrapure water measurements.

In-line Monitor/controllers are generally used in the moredemanding Dl water applications. Increased accuracy isrealized since the degrading effect of carbon dioxide on highpurity water is avoided by use of an in-line sensor (cell). Thissame degradation of ultrapure water is the reason there are noresistivity calibration standard solutions (as with conductivityinstruments). Electronic sensor substitutes are normally usedto calibrate resistivity Monitor/controllers.

Myron L Company manufactures a variety of in-line instruments

including resistivity Monitor/controllers which are designedspecically for Dl water. Seven resistivity ranges are availableto suit any Dl water application: 0-20 megohm, 0-10 megohm0-5 megohm, 0-2 megohm, 0-1 megohm, 0-500 kilohmand 0-200 kilohm. Temperature compensation is automaticand achieved via a dual thermistor circuit. Monitor/controllemodels contain an internal adjustable set point, Piezo alarmconnectors and a heavy-duty 10 amp relay circuit which can beused to control an alarm, valves, pump, etc. Available optionsinclude 4-20 milliamp output, 3 sensor input, 3 range capabilityand temperature. Internal electronic sensor substitutes arestandard on all Monitor/controllers.

Sensors are available constructed in either 316 stainless

steel or titanium. All sensors are provided with a 3/4" MNPTpolypropylene bushing and 10 ft./3 meters of cable. OptionaPVDF or stainless steel bushings can be ordered, as well aslonger cable lengths up to 100 ft./30 meters.

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The following table briey covers Myron L Company instruments for Dl water applications. For details and recommendations, pleaserefer to Myron L data sheets, visit our website (www.myronl.com), or contact us by phone, fax, or email (sales@myronl.com).

DISYSTEM

WATER QUALITY HANDHELDINSTRUMENTS

RESISTIVITYMONITOR/CONTROLLERS

CONDUCTIVITYMONITOR/CONTROLLERS

Two Bed,WeakBase

Anion

20,000-50,000 ohms(50-20 S)

Model

6PIIFCE

4PII9PTK

PT1EPEP-10532M1

Display

digitaldigitaldigital

digitalanaloganaloganalog

Readout

kilohmkilohmkilohm

SM/MMM

Model

752II-17753II-17

Aquaswitch I*

Display

analogdigital

Readout

kilohmkilohm

Model

756II-111

757II-111Aquaswitch I*

Display

analog

analog

Readout

SS

Two BedStrongBaseAnion

50,000-200,000 ohms(20-5 S)

6PIIFCE

4PII9PTKPT1EP

EP-10532M1

digitaldigitaldigitaldigitalanaloganaloganalog

kilohmkilohmkilohm

SM/M

MM

752II-17753II-17

Aquaswitch I*

analogdigital

kilohmkilohm

756II-109757II-109758II-109

Aquaswitch I*

analogdigitaldigital

SSS

0.05-2.0 megohm(20-0.5 S)

6PIIFCE

4PIIEP

digitaldigitalanalog

S/MS/MM/M

752II-14753II-14

Aquaswitch I*

analogdigital

megohmmegohm

756II-109757II-109758II-109

Aquaswitch I*

analogdigitaldigital

SSS

Mixed Bed 1-18.23 megohm

(1-0.055 S)

6PIIFCE

4PIIEP

digital

digitalanalog

S/M

S/MM/M

752II-11

753II-11Aquaswitch I*

analog

digital

megohm

megohm

756II-101

757II-101758II-101

Aquaswitch I*

analog

digitaldigital

S

SS

18.2megohm

10megohm

5megohm

1megohm

100,000ohms

10,000ohms

1,000ohms

100ohms

20ohms

10ohms

1ohms

0.055siemens

0.1siemens

0.2siemens

1siemens

10siemens

100siemens

1,000siemens

10,000siemens

50,000siemens

100,000siemens

1mho

ULTRAPURE PUREWATER PUREWATER CITYSUPPLIES SEAWATER

RESISTIVITY VS. CONDUCTIVITY

Examples: 1 micromho (mho) = 1 microsiemen (S); 0.5 microsiemens = 2 megohms (2,000,000 ohms)

200 kilohm (200,000 ohms) = 0.2 megohm = 5 microsiemens

USEFUL CONVERSIONS

1megohm

microsiemens(micromho)

1microsiemens

(micromho)megohm= =

*Note: Aquaswitch I does not monitor water quality itself, but must be used withour Myron L Company 750 II resistivity or conductivity/TDS Monitor/controllers.

Myron L Company 2012 DIAB 05-12

Built On Trust. Founded in 1957, the Myron L Companyis one of the worlds leading manufacturers of water qualityinstruments. Because of our commitment to productimprovement, changes in design and specications arepossible. You have our assurance any changes will be guidedby our product philosophy: accuracy, reliability, and simplicity.

2450 Impala Drive

Carlsbad, CA 92010-7226 USA

Tel: +1-760-438-2021

Fax: +1-800-869-7668 / +1-760-931-9189

www.myronl.com

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