Archive for September, 2012

pH and pH Meters – MyronLMeters.com

Posted by 24 Sep, 2012

TweetWhat is pH? pH measures the activity of the (solvated) hydrogen ion. Pure water has a pH very close to 7 at 25°C. Solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic or alkaline. The pH scale is traceable to a set of standard solutions […]

What is pH?

pH measures the activity of the (solvated) hydrogen ion. Pure water has a pH very close to 7 at 25°C. Solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic or alkaline. The pH scale is traceable to a set of standard solutions whose pH is established by international agreement. Measuring pH for aqueous solutions can be done with a glass electrode and a pH meter, or using indicators.

Measuring pH is important in water treatment, medicine, biology, chemistry, agriculture, forestry, food science, environmental science, oceanography, civil engineering, chemical engineering, and many other applications.

p[H] was first introduced by Danish chemist Søren Peder Lauritz Sørensen at the Carlsberg Laboratory in 1909 and revised to the modern pH in 1924 to accommodate definitions and measurements in terms of electrochemical cells.  According to the Carlsberg Foundation pH stands for “power of hydrogen”.

pH is defined as the decimal logarithm of the reciprocal of the hydrogen ion activity, aH+, in a solution.

pH Meters

A pH meter is an electronic device used for measuring the pH (acidity or alkalinity) of a liquid (though special probes are sometimes used to measure the pH of semi-solid substances). A typical pH meter consists of a special measuring probe (a glass electrode) connected to an electronic meter that measures and displays the pH reading.

The probe

The pH probe measures pH as the activity of the hydrogen cations surrounding a thin-walled glass bulb at its tip. The probe produces a small voltage (about 0.06 volt per pH unit) that is measured and displayed as pH units by the meter. For more information about pH probe care or replacement, please consult your Myron L meter operations manual.

Calibration and use

*Please consult your Myron L meter operations manual before calibrating.

For very precise work the pH meter should be calibrated before each measurement. For normal use calibration should be performed at the beginning of each day. The reason for this is that the glass electrode does not give a reproducible e.m.f. over longer periods of time. Calibration should be performed with at least two standard buffer solutions that span the range of pH values to be measured. For general purposes buffers at pH 4 and pH 10 are acceptable. The pH meter has one control (calibrate) to set the meter reading equal to the value of the first standard buffer and a second control (slope) which is used to adjust the meter reading to the value of the second buffer. A third control allows the temperature to be set. Standard buffer solutions, which can be obtained from MyronLMeters.com here:

http://www.myronlmeters.com/pH-Buffer-Calibration-Solutions-s/82.htm

usually state how the buffer value changes with temperature. For more precise measurements, a three buffer solution calibration is preferred. As pH 7 is essentially, a “zero point” calibration (akin to zeroing a scale), calibrating at pH 7 first, calibrating at the pH closest to the point of interest ( e.g. either 4 or 10) second and checking the third point will provide a more linear accuracy to what is essentially a non-linear problem. Some meters will allow a three point calibration and that is the preferred scheme for the most accurate work, and is recommended by Myron L Meters. Higher quality meters will have a provision to account for temperature coefficient correction, and high-end pH probes have temperature probes built in. The calibration process correlates the voltage produced by the probe (approximately 0.06 volts per pH unit) with the pH scale. After each single measurement, the probe is rinsed with distilled water or deionized water to remove any traces of the solution being measured, blotted with a scientific wipe to absorb any remaining water which could dilute the sample and thus alter the reading, and then quickly immersed in another solution.

Storage conditions of the glass probes

When not in use, the glass probe tip must be kept wet at all times to avoid the pH sensing membrane dehydration and the subsequent dysfunction of the electrode. You can get your sensor storage solution here:

http://www.myronlmeters.com/pH-Storage-Solution-p/s-ssq.htm

A glass electrode alone (i.e., without combined reference electrode) is typically stored immersed in an acidic solution of around pH 3.0. In an emergency, acidified tap water can be used, but distilled or deionised water must never be used for longer-term probe storage as the relatively ionless water “sucks” ions out of the probe membrane through diffusion, which degrades it.

Combined electrodes (glass membrane + reference electrode) are better stored immersed in the bridge electrolyte (often KCl  3 M) to avoid the diffusion of the electrolyte (KCl) out of the liquid junction.

Cleaning and troubleshooting of the glass probes

Occasionally (about once a month), the probe may be cleaned using pH-electrode cleaning solution; generally a 0.1 M solution of hydrochloric acid (HCl) is used, having a pH of one.

In case of strong degradation of the glass membrane performance due to membrane poisoning, diluted hydrofluoric acid (HF < 2 %) can be used to quickly etch (< 1 minute) a thin damaged film of glass. Alternatively a dilute solution of ammonium fluoride (NH4F) can be used. To avoid unexpected problems, the best practice is however to always refer to the electrode manufacturer recommendations or to a classical textbook of analytical chemistry.

Types of pH meters

A pH meter for every industry

pH meters range from simple and inexpensive pen-like devices to complex and expensive laboratory instruments with computer interfaces and several inputs for indicator and temperature measurements to be entered to adjust for the slight variation in pH caused by temperature. Specialty meters and probes are available for use in special applications, harsh environments, etc. Myron L Meters offers a simple pen-style pH meter, analog handheld meters, digital handheld multiparameter meters, and inline monitor/controllers.

Myron L Ultrapen PT2 pH and Temperature Tester

 

 

 

 

 

 

 

 

https://www.myronlmeters.com/Ultrapen-PT2-Multiparameter-Meter-p/dh-up-pt2-ss.htm

ULTRAPEN PT2 pH and Temperature Pen

Accuracy of +/- 0.01 pH

Reliable Repeatable Results

Easy Calibration

Automatic Temperature Compensation

Measures Temperature

Durable, Fully Potted Circuitry

Waterproof

Comes with 2oz bottle of pH Storage Solution

 

 

Myron L AG-6 TDS and pH meter

 

 

 

 

 

 

 

 

 

http://www.myronlmeters.com/Analog-pH-Conductivity-Meter-p/ah-ds-ag6-fslash-ph.htm

 

Agri-Meter – Ag-6: 0-5 millimhos; 2-12 pH

Instant and accurate TDS tests

Electronic Internal Standard for easy field calibration

Fast Auto Temperature Compensation

Rugged design for years of trouble-free testing

Simple to use

 

Myron L Ultrameter II 6P multiparameter meter

 

 

 

 

 

 

 

 

 

http://www.myronlmeters.com/Ultrameter-II-6P-Multiparameter-Meter-p/dh-umii-6pii.htm

 

 

Multi-Parameter: Conductivity, TDS, Resistivity, pH, ORP, Temperature, Free Chlorine (FCE)

+/-1% Accuracy of Reading

Memory Storage: Save up to 100 samples w/ Date & Time stamp

Wireless Download Module Optional

Waterproof

 

Myron L 723II digital inline pH monitor/controller

 

 

 

 

 

 

 

 

 

http://www.myronlmeters.com/Inline-pH-Digital-Monitor-Controller-p/i-dmc-723ii.htm

 

The advanced “isolated” circuitry of the 720 Series II pH/ORP Monitor/ controllers guarantees accurate and reliable measurements — completely eliminating ground-loop and noise issues.

 

The unique sensor preamp allows for longer distances between the sensor and the Monitor/controller without the loss of accuracy or reliability.

 

All Myron L Monitor/controllers feature a highly refined and precise Temperature Compensation circuit. This feature perfectly matches the NERNST equation correcting the displayed reading to 25′C. The TC may be disabled to conform to USP requirements.

 

 

Categories : Product Updates, Science and Industry Updates

Ultrapen PT3 pen – Tests ORP / REDOX and Temperature – MyronLMeters.com

Posted by 23 Sep, 2012

TweetThe All NEW ULTRAPEN PT3 pen tests ORP / REDOX and Temperature with great reliability. Advanced features include highly stable microprocessor-based circuitry; automatic temperature compensation from 15ºC to … [Learn more about the ULTRAPEN PT3 pen NOW!]

The All NEW ULTRAPEN PT3 pen tests ORP / REDOX and Temperature with great reliability. Advanced features include highly stable microprocessor-based circuitry; automatic temperature compensation from 15ºC to … [Learn more about the ULTRAPEN PT3 pen NOW!]

Ultrapen PT3 instrument diagram

Categories : Product Updates

Conductivity and Conductivity Meters – MyronLMeters.com

Posted by 23 Sep, 2012

TweetThe conductivity (or specific conductance) of a solution is a measure of its ability to conduct electricity. The standard unit of conductivity is siemens per meter (S/m). Conductivity measurements are used routinely in many industrial and environmental applications as a fast, inexpensive and reliable way of measuring ionic content in a solution. For example, the […]

The conductivity (or specific conductance) of a solution is a measure of its ability to conduct electricity. The standard unit of conductivity is siemens per meter (S/m).

Conductivity measurements are used routinely in many industrial and environmental applications as a fast, inexpensive and reliable way of measuring ionic content in a solution. For example, the measurement of product conductivity is a typical way to monitor and continuously trend the performance of water purification systems.

In many cases, conductivity is linked directly to the total dissolved solids (TDS). High quality deionized water has a conductivity of about 5.5 μS/m, typical drinking water in the range of 5-50 mS/m, while sea water about 5 S/m (i.e., sea water’s conductivity is one million times higher than deionized water).

Conductivity is traditionally determined by measuring the AC resistance of the solution between two electrodes.

Resistivity of pure water (in MΩ-cm) as a function of temperature

The standard unit of conductivity is S/m and usually refers to 25 °C (standard temperature). Often encountered in industry is the traditional unit of μS/cm. 106 μS/cm = 103 mS/cm = 1 S/cm. The numbers in μS/cm are higher than those in μS/m by a factor of 100 (i.e., 1 μS/cm = 100 μS/m). Occasionally a unit of “EC” (electrical conductivity) is found on scales of instruments: 1 EC = 1 μS/cm. Sometimes encountered is a so-called mho (reciprocal of ohm): 1 mho/m = 1 S/m. Historically, mhos antedate Siemens by many decades; good vacuum-tube testers, for instance, gave transconductance readings in micromhos.

The commonly used standard cell has a width of 1 cm, and thus for very pure water in equilibrium with air would have a resistance of about 106 ohm, known as a megohm. Ultra-pure water could achieve 18 megohms or more. Thus in the past megohm-cm was used, sometimes abbreviated to “megohm”. Sometimes conductivity is given just in “microSiemens” (omitting the distance term in the unit). While this is an error, it’s usually assumed to be equal to the traditional μS/cm. The typical conversion of conductivity to the total dissolved solids is done assuming that the solid is sodium chloride: 1 μS/cm is then an equivalent of about 0.6 mg of NaCl per kg of water.

A conductivity meter and probe

The electrical conductivity of a solution is measured by determining the resistance of the solution between two flat or cylindrical electrodes separated by a fixed distance. An alternating voltage is used in order to avoid electrolysis. The resistance is measured by a conductivity meter. Typical frequencies used are in the range 1–3 kHz. The dependence on the frequency is usually small, but may become appreciable at very high frequencies, an effect known as the Debye–Falkenhagen effect.

A wide variety of instrumentation is commercially available. There are two types of cell, the classical type with flat or cylindrical electrodes and a second type based on induction. Many commercial systems, Myron L meters, e.g.,  offer automatic temperature correction.

MyronLMeters.com offers many reliable conductivity meters – some analog, some digital, some pen-style, some multiparameter – but all accurate, reliable, and easy-to-use.

Myron L analog handheld conductivity meter 512M5

 

 

 

 

 

 

 

 

 

Analog Handheld conductivity meter

512M5: 0-5000 micromhos/microsiemens

Instant and accurate Conductivity tests

Electronic Internal Standard for easy field calibration

Fast Auto Temperature Compensation

Rugged design for years of trouble-free testing

Simple to use

 

Myron L Digital Handheld Conductivity, TDS, Salinity Pen

 

 

 

 

 

 

 

 

 

Digital Handheld Conductivity, TDS, Salinity Pen

ULTRAPEN PT1 Conductivity – TDS – Salinity Pen

Accuracy of +/-1% of READING (+/-.2% at Calibration Point)

Reliable Repeatable Results

Solution modes: KCl, NaCl and 442

Automatic Temperature Compensation

Autoranging

Durable, Fully Potted Circuitry

Waterproof

 

Myron L Digital Handheld Multiparameter Meter: Ultrameter 6P II FCe

 

 

 

 

 

 

 

 

 

Digital Handheld Multi-Parameter meter: Conductivity, TDS, Resistivity, pH, ORP, Temperature, Free Chlorine (FCE)
+/-1% Accuracy of Reading
Memory Storage: Save up to 100 samples w/ Date & Time stamp
Wireless Download Module Optional
Waterproof

 

Myron L digital inline conductivity monitor/controller 758II

 

 

 

 

 

 

 

 

 

Digital In-Line Conductivity Monitor/Controller

The unique circuitry of our 750 Series II Conductivity Inline Meters guarantees accurate and reliable measurements. Drift-free performance is assured by “field proven” electronics, including automatic DC offset compensation and highly accurate drive voltage.

Since Temperature Compensation is at the heart of accurate water measurement, all Myron L Monitor/controllers feature a highly refined and precise TC circuit. This feature perfectly matches the water temperature coefficient as it changes. All models are corrected to 25′C. The TC may be disabled to conform to USP requirements.

 

 

Categories : Product Updates, Technical Tips

Circuit Board Cleanliness Testing – MyronLMeters.com

Posted by 19 Sep, 2012

TweetContamination of circuit boards can bring about severe degradation of insulation resistance and dielectric strength. Cleanliness of completed circuit boards is, therefore, of vital interest. For those companies who have established circuit board cleaning procedures, the MIL Spec P-28809 has been used as a guideline for control. Now a simple “on line” test for the […]

Contamination of circuit boards can bring about severe degradation of insulation resistance and dielectric strength. Cleanliness of completed circuit boards is, therefore, of vital interest.

For those companies who have established circuit board cleaning procedures, the MIL Spec P-28809 has been used as a guideline for control. Now a simple “on line” test for the relative measurement of ionic contamination has been developed.

This fast and economical method for testing circuit board cleanliness uses an Ultrameter II™ 4P or 6P, a suitable container, and a mixture of Dl (deionized) water and alcohol. The procedure is as follows:

1. Mix a stock quantity of solution using 25 parts by volume of Dl water and 75 parts by volume of 99% isopropyl alcohol. The conductivity, measured with the Ultrameter II 4P or 6P should be a maximum of 0.166 micromhos/microseimens/cm.

2. Measure out an amount of the water/alcohol mixture equal to 100 ml per 10 square inches of circuit board surface to be tested (considering both sides of the board but not components), and add 60 ml additional. In other words: 2(L X W) (10 ml) + 60 ml = total solution needed.

3. Fill a poly “zip-lock” bag or other suitable plastic or glass container with the measured water/alcohol solution.

4. Using the measured water/alcohol solution in the poly bag, rinse out the Ultrameter II’s cell cup three (3) times, discarding the rinse solution each time. Fill the instrument cell cup a fourth time and take a meter reading. This value should be 0.166 micromhos/microseimens/cm or less and is the very clean control (or “comparison”) reading for the test.

5. Being very careful not to contaminate the PCB, totally immerse the circuit board in the solution. Seal bag. Allow it to soak for three (3) minutes with mild agitation.

6. At the conclusion of the soaking, pour the solution directly into the instruments cell cup four (4) times; take the fourth reading.

7. Compare the control reading in Step 4 with the reading taken in Step 6 (The higher the difference between the two readings, the greater the ionic contamination). Record this final extract reading for comparison with other boards tested in the same manner.

The level of cleanliness needed can be determined by each individual company.

Mil Spec P-28809 can be used as a guideline, or standards can be established based upon available data. In either event, the comparative method using the Myron L Ultrameter II will assist in the determination of that level of cleanliness.

 

 

Categories : Application Advice, Technical Tips

Saving With Automatic Rinse Tank Controls – MyronLMeters.com

Posted by 18 Sep, 2012

TweetProper rinsing is one of the most important steps in quality manufacturing or metal finishing. Plenty of low cost, good quality water for rinsing has been available in the past, so rinse water conservation has been largely ignored. Today, this is no longer true. Tap water costs have increased dramatically. Various new regulations are now […]

Proper rinsing is one of the most important steps in quality manufacturing or metal finishing. Plenty of low cost, good quality water for rinsing has been available in the past, so rinse water conservation has been largely ignored.

Today, this is no longer true. Tap water costs have increased dramatically. Various new regulations are now in effect which limit the allowable volume of wastewater. Others require wastewater treatment. Still other laws tax the amount of water going down the sewer.

These factors have all encouraged many manufacturers and platers to invest in automatic rinse tank control systems. Many platers using automatic control systems for the first time are pleased to discover a reduction in water usage of up to 80%.

This water use reduction provides two major benefits:

1. LOWER WATER BILLS

The savings possible with Myron L automatic Rinse Tank CONTROLSTIK II™ Systems are illustrated in the following table. Figures are based on a 50% water reduction rate; the minimum that can usually be expected. Exact savings depend on several variables, including the type and frequency of workloads, rinse tank size, and type of contaminant.

NOTE: 100 cubic feet of water is equivalent to 2831.5 liters/748 gallons.

 

 

 

 

 

 

2. WASTE TREATMENT SYSTEM INVESTMENT IS REDUCED.

The second major cost advantage of the CONTROLSTIK II™ System: Reducing the investment required for waste treatment equipment. Because less water is handled, smaller capacity treatment/recovery systems can be used to meet government water pollution regulations.

Generally, chemicals being “dragged in” and salts that are dissolved from work being rinsed cause rinse water contamination. These solutions ionize and can be measured and controlled by Electrical Conductivity (EC). EC measures both the total dissolved solids and the non-solid (eg: acid) contaminants, thereby giving the most correct method of control. As water contamination increases, so does the conductivity; the automatic rinse tank controls operate on this principle. When conductivity reaches the value selected as a control point, the water valve turns on to dilute the contamination. When the contaminants are reduced by the dilution, the conductivity falls and the water valve turns off.

The unit of measurement for conductivity is the micromhos (microseimens); Myron L systems are calibrated to this unit. All Myron L Rinse Tank CONTROLSTIK II Systems can be used in either normal tap water or in Deionized (DI) water tanks. The dual range sensor can be set on either the 5-500 or the 500-5000 micromhos range. The AUTOMATIC RINSE TANK CONTROL is briefly described below. All Myron L CONTROLSTIK II Systems consist of three components: Transformer Box, CONTROLSTIK Sensor, and Solenoid Valve.

AUTOMATIC RINSE TANK MODEL

Model: 597

Features

Reliable solid-state electronics in a heavy-duty, IP65/NEMA 4X Corrosion and water resistant transformer box enclosure, suitable for any plating environment.

OTHER PRODUCTS USEFUL FOR FINISHING APPLICATIONS

Also available are hand-held Conductivity & pH Instruments for “on-the-spot” water quality testing. The Conductivity and pH sensors are built in for maximum protection. The pH sensor is user replaceable. 750 Series II Monitor/controllers for continuous in-line water quality monitoring. For additional information, please refer to Myron L data sheets, or Ask An Expert at MyronLMeters.com.

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Categories : Application Advice, Technical Tips

Boiler and Cooling Tower Water – MyronLMeters.com

Posted by 15 Sep, 2012

TweetBoilers and cooling towers share two major water related problems: deposits and corrosion. As a boiler or water evaporating from a cooling tower generates steam, dissolved minerals are left behind, increasing the concentration of these minerals. Additional minerals are introduced via the water added to makeup the water lost to steam/evaporation. Eventually, the minerals reach […]

Boilers and cooling towers share two major water related problems: deposits and corrosion. As a boiler or water evaporating from a cooling tower generates steam, dissolved minerals are left behind, increasing the concentration of these minerals. Additional minerals are introduced via the water added to makeup the water lost to steam/evaporation. Eventually, the minerals reach a level (or cycle) of concentration that will cause either loss of efficiency due to scale or damage from corrosion. This level can be determined by the Ryznar or Langlier indices and correlated to a conductivity or TDS range. Most people recognize problems associated with corrosion. Effects from scale deposits, however, are equally important. For example, as little as 1/8″ of scale can reduce the efficiency of a boiler by 18% or a cooling tower heat exchanger by 40%!

A variety of water treatment methods are employed in an effort to control these problems. Even with water treatment, it is still necessary to regularly blow down or bleed off part of the concentrated water and make up with lower salinity water to reduce the overall mineral concentration.

To conserve water and treatment chemicals, it is desirable to allow the dissolved minerals to reach a maximum cycle of concentration while still avoiding problems. Because feed water/make-up waters vary in the types and amounts of minerals present, the allowable cycles of concentration will vary. As a result, regular testing of boiler and cooling waters is essential to optimize water treatment programs and blow down schedules. Tests commonly performed include conductivity or TDS, pH and ORP. Myron L meters provide you with a simple, fast, and accurate means of testing these parameters.

Many cooling towers and boilers have inline controllers used to release water from the tower or boiler and feed chemical(s) into the system. The controllers must be calibrated regularly to ensure fouling or drift of the sensor has not occurred. Our portable instruments in conjunction with NIST traceable standard solutions provide rapid verification of the accuracy of inline controllers. This method reduces manpower and the likelihood of disturbing or damaging sensors.

Conductivity

Conductivity is the measurement of a solution’s ability to transmit an electrical current. It is usually expressed in microsiemens/cm (micromhos/cm). Pure water is actually a poor electrical conductor (18,200,000 ohms/cm of resistance). It is the amount of ionized substances (or salts) dissolved in water, which determines the conductivity. Because the vast majority of the dissolved minerals in water are these conductive inorganic impurities, conductivity measurement is an excellent indicator of mineral concentration.

Myron L meters were developed for just this purpose. Models are available which display conductivity and/or ppm of TDS. For detailed information regarding the relationship between conductivity and TDS, please see the our Application Bulletin: Standard Solutions and Buffers.

pH

pH, the measurement of acid or base, is one of the most important factors affecting scale formation or corrosion in a boiler or cooling system. The types of impurities comprising the mineral concentration behave differently at various pHs. Low pH waters have a tendency to cause corrosion, while high pH waters may cause scale formation.

Boiler water

Boiler water requirements can range from very pure to more than 6500 microsiemens, depending on size, pressure, application, and feed water. Once the maximum cycles of concentration has been established, a conductivity instrument can conveniently help you to determine if the blow down schedule is adequate. Samples should be cooled to at least 160°F/71°C to ensure accurate temperature compensated readings.

Boiler condensate

Boiler condensate samples are often tested to determine if there is any carryover of boiler water solids or contaminants entering from outside the system. Condensate is relatively pure water, and values of 2-100 microsiemens are common. Because of these low values, a multiple-range instrument is recommended to increase the resolution and accuracy of the reading. Monitoring the pH of condensate is also important since condensate is very corrosive at low pHs. Treatment additives are often added to elevate the pH to minimize corrosion in condensate lines.

Cooling tower water

Cooling tower water has become more challenging since the reduced use of acid and the elimination of chromate. Monitoring conductivity and pH has become imperative to maintain a proper treatment program. Although many systems have controls on these parameters, the possibility of a system upset is always present. Even slight upsets can cause rapid scaling of heat exchangers.

Biological Growth

Biological growth is another extremely important facet to proper cooling water management. Microbes can cause corrosion, fouling, and disease. Oxidizing biocides (chlorine, chlorine dioxide, ozone and bromine) have been employed to keep bacteria under control. Monitoring of the ORP (Oxidation Reduction Potential)/redox is very useful in its ability to correlate millivolt readings to sanitization strength of the water. The ULTRAMETER II™ 6P includes this parameter for quick on-site determinations.

Ultrameter II 4P  Ultrameter II 6P  TechPro II TH1  TechPro II TP1  TechPro II TPH1  M6/pH

EP11/pH   512M5   EP10  EP  inline monitors/controllers

Categories : Application Advice, Technical Tips

Application Bulletin: Deionized Water – MyronLMeters.com

Posted by 15 Sep, 2012

TweetYears ago, high purity water was used only in limited applications. Today, deionized (Dl) water has become an essential ingredient in hundreds of applications including: medical, laboratory, pharmaceutical, cosmetics, electronics manufacturing, food processing, plating, countless industrial processes, and even the final rinse at the local car wash. THE DEIONIZATION PROCESS The vast majority of dissolved […]

Years ago, high purity water was used only in limited applications. Today, deionized (Dl) water has become an essential ingredient in hundreds of applications including: medical, laboratory, pharmaceutical, cosmetics, electronics manufacturing, food processing, plating, countless industrial processes, and even the final rinse at the local car wash.

THE DEIONIZATION PROCESS

The vast majority of dissolved impurities in modern water supplies are ions such as calcium, sodium, chlorides, etc. The deionization 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 affinity for other ions. The ion exchange process occurs on the binding sites of the resin beads. Once depleted of exchange capacity, the resin bed is regenerated with concentrated acid and caustic which strips 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 continuous units. A two-bed system employs separate cation and anion resin beds. Mixed-bed deionizers utilize both resins in the same vessel. The highest quality water is produced by mixed-bed deionizers, while two-bed deionizers have a larger capacity. Continuous deionizers, mainly used in labs for polishing, do not require regeneration.

TESTING Dl WATER QUALITY

Water quality from deionizers varies with the type of resins used, feed water quality, flow, efficiency of regeneration, remaining capacity, etc. Because of these variables, it is critical in many Dl water applications to know the precise quality. Resistivity/ conductivity is the most convenient method for testing Dl water quality. Deionized pure water is a poor electrical conductor, having a resistivity of 18.2 million ohm-cm (18.2 megohm) and conductivity of 0.055 microsiemens. It is the amount of ionized substances (or salts) dissolved in the water which determines water’s ability to conduct electricity. Therefore, resistivity and its inverse, conductivity, are good general purpose quality parameters.

Because temperature dramatically affects the conductivity of water, conductivity measurements are internationally referenced to 25°C to allow for comparisons of different samples. With typical water supplies, temperature changes the conductivity an average of 2%/°C, which is relatively easy to compensate. Deionized water, however, is much more challenging to accurately measure since temperature effects can approach
10%/°C! Accurate automatic temperature compensation, therefore, is the “heart’ of any respectable instrument.

RECOMMENDED INSTRUMENTATION

Portable instruments are typically used to measure Dl water quality at points of use, pinpoint problems in a Dl system confirm monitor readings, and test the feed water to the system. The handheld Myron L meters have been the first choice of Dl water professionals for many years. For two-bed Dl systems, there are several usable models with displays in either microsiemens or ppm (parts per million) of total dissolved solids. The most versatile instruments for Dl water is the 4P or 6P Ultrameter II™, which can measure both ultrapure mixed- bed quality water and unpurified water. It should be noted that once Dl water leaves the piping, its resistivity will drop because the water absorbs dissolved carbon dioxide from the air. Measuring of ultrapure water with a hand-held instrument requires not only the right instrument, but the right technique to obtain accurate, repeatable readings. Myron L meters offer the accuracy and precision necessary for ultrapure water measurements.

In-line Monitor/controllers are generally used in the more demanding Dl water applications. Increased accuracy is realized since the degrading effect of carbon dioxide on high purity water is avoided by use of an in-line sensor (cell). This same degradation of ultrapure water is the reason there are no resistivity calibration standard solutions (as with conductivity instruments). Electronic sensor substitutes are normally used to calibrate resistivity Monitor/controllers.

Myron L manufactures a variety of in-line instruments, including resistivity Monitor/controllers which are designed specifically for Dl water. Seven resistivity ranges are available to suit any Dl water application: 0-20 megohm, 0-10 megohm,
0-5 megohm, 0-2 megohm, 0-1 megohm, 0-500 kilohm, and 0-200 kilohm. Temperature compensation is automatic and achieved via a dual thermistor circuit. Monitor/controller models contain an internal adjustable set point, Piezo alarm connectors and a heavy-duty 10 amp relay circuit which can be used to control an alarm, valves, pump, etc. Available options include 4-20 milliamp output, 3 sensor input, 3 range capability and temperature. Internal electronic sensor substitutes are standard on all Monitor/controllers.

Sensors are available constructed in either 316 stainless steel or titanium. All sensors are provided with a 3/4″ MNPT polypropylene bushing and 10 ft./3 meters of cable. Optional PVDF or stainless steel bushings can be ordered, as well as longer cable lengths up to 100 ft./30 meters.

For details  and recommendations, please refer to Myron L data sheets, visit our website (www.myronlmeters.com), or contact us by email (myronlmeters@gmail.com).

 

 

 

Categories : Technical Tips