Tweet **For use with 750II Series Monitor/controllers** NIST traceable Calibration Modules are commonly used to verify and calibrate Resistivity Monitor/controllers. Normally they are not needed due to the “built-in” electronic calibration or “Full Scale Test”. However, your requirements may be such that a crosscheck or verifi cation is required. If the proper Resistivity Sensor Substitute […]
Tweet All Myron L meters are factory calibrated with NIST traceable Standard Solutions having specific conductivity/ppm values. Myron L solutions are made under strictly controlled conditions using reagent grade salts. These salts are […]
All Myron L meters are factory calibrated with NIST traceable Standard Solutions having specific conductivity/ppm values. Myron L solutions are made under strictly controlled conditions using reagent grade salts. These salts are mixed with deionized water having a resistivity of at least 5 megohms-cm purity.
Myron L solutions have an accuracy of ±1% based on values published in the International Critical Tables and traceable to the National Institute of Standards and Technology.
Myron L conductivity Standard Solutions and pH Buffers listed below are used for factory calibration. Regular use of these solutions is recommended to ensure specified instrument accuracy. Frequency of conductivity recalibration depends upon use, but once every month should be sufficient for an instrument used daily. pH models, depending upon use, should be recalibrated with pH 7 Buffer every 1-2 weeks, and checked with pH 4 and/or 10 Buffers at similar intervals. pH Sensor Storage Solution is recommended for keeping the pH sensor wet. Myron L solutions are available in quart/1 ltr., gallon/3,8 ltr. and 2 oz./59 ml plastic bottles, ready to use.
Note: Refer to TDS/Conductivity Equivalents chart for actual calibration point values.
Note: RE-10 Range Extenders are usually calibrated with either 442-15,000 or 442- 30,000 Standard Solution.
Conductivity instruments are a convenient way to determine the parts per million of total dissolved solids (ppm/TDS) in boilers, cooling towers, reverse osmosis systems, etc. Although the International Unit (Sl) of measuring conductivity is the microsiemens/ cm (also known as micromhos/cm), a direct reading in ppm/TDS is sometimes preferred.
Myron L® conductivity instruments and monitor/ controllers are calibrated to read in ppm/442, ppm/ NaCI, or microsiemens. All three values are listed on our Standard Solutions. The relationship among these standards can be seen in the table and graphs that follow.
442 Natural Water™ Standard Solution is used in calibrating many Myron L® Instruments. It is the best choice when measuring boiler and cooling water samples, city water supply, lakes, wells, etc. “442” refers to the combination of salts mixed with deionized water to comprise this standard: 40% sodium sulfate, 40% sodium bicarbonate, 20% sodium chloride. A combination of standard salts is necessary since natural water salt type and concentration can vary greatly by location. After much research, the 442 Standard was developed by the Myron L® Company more than 40 years ago. It remains the world’s most accepted standard.
NaCl Standard Solution is offered to calibrate instruments that measure any sample that is predominately NaCI (sodium chloride), such as sea water, brackish water, etc. As can be seen in the graph at right, 1000 ppm of NaCI has a conductivity of 2000 micromhos. Note how this 1:2 relationship is continuously variable throughout the curve and decreases as ppm NaCI increases.
KCl Standard Solution is used to calibrate conductivity instruments that read directly in microsiemens (micromhos) or millisiemens (1000 microsiemens). KCI (potassium chloride) is a very stable salt and is an international calibration standard for conductivity measurement.
pH Buffer Solutions 4, 7 and 10 are mold inhibited and accurate to within + 0.01 pH units @ 25°C. Myron L Buffers are traceable to NIST certified pH references and are color-coded for instant identification.
You can find your Myron L solutions here: http://www.myronlmeters.com/Myron-L-Calibration-Solutions-s/45.htm
The table below shows the Conductivity/TDS Equivalents for various Myron L Standard Solutions.
TweetAnyone and everyone who is responsible for operating and maintaining a swimming pool or spa has to test, monitor, and control complex, interdependent chemical factors that affect the quality of water bathers are immersed in. Additionally, aquatic facilities operators must be familiar with all laws, regulations, and guidelines governing what these parameters should be. Why? […]
Anyone and everyone who is responsible for operating and maintaining a swimming pool or spa has to test, monitor, and control complex, interdependent chemical factors that affect the quality of water bathers are immersed in. Additionally, aquatic facilities operators must be familiar with all laws, regulations, and guidelines governing what these parameters should be.
Why? Because the worst breeding ground for any kind of microorganism is a warm (enough) stagnant pool of water. People plus stagnant water equals morbid illness. That’s why pools have to be circulated, filtered, and sanitized – with any number of chemicals or methods, but most frequently with chlorine compounds. However, adding chemicals that kill the bad microorganisms can also make the water uncomfortable, and in some cases unsafe, for swimmers. Additionally, if all the chemical factors of the water are not controlled, the very structures and equipment that hold the water and keep it clean are ruined.
So the pool professional must perform a delicate balancing act with all the factors that affect both the health and comfort of bathers and the equipment and structures that support this. Both water balance – or mineral saturation control – and sanitizer levels must constantly be maintained. This is achieved by measuring pertinent water quality factors and adding chemicals or water to keep the factors within acceptable parameters.
Water is constantly changing. Anything and everything directly and indirectly affects the relationship of its chemical parameters to each other: sunlight, wind, rain, oil, dirt, cosmetics, other bodily wastes, and any chemicals you add to it. Balanced water not only keeps swimmers comfortable, but also protects the pool shell, plumbing, and all other related equipment from damage by etching or build-up and stains.
The pool professional is already well acquainted with pH, Total Alkalinity (TA), and Calcium Hardness (CH); along with Total Dissolved Solids (TDS) and Temperature, these are the factors that influence water balance. Water that is in balance is neither aggressive nor oversaturated.
Aggressive water lacks sufficient calcium to saturate the water, so it is hungry for more. It will eat anything it comes into contact with to fill its need, including the walls of your pool or spa or the equipment it touches. Over-saturated water cannot hold any more minerals, so dissolved minerals come out of solution and form scale on pool and equipment surfaces.
The pH of pool water is critical to the effectiveness of the sanitizer as well as the water balance. pH is determined by the concentration of Hydrogen ions in a specific volume of water. It is measured on a scale of 0-14, 0-7 being acidic and 7-14 being basic.
You must maintain the pH of the water at a level that assures the sanitizer works effectively and at the same time protects the pool shell and equipment from corrosion or scaling and the bathers from discomfort or irritation. If the pH is too high, the water is out of balance, and the sanitizer’s ability to work decreases. More and more sanitizer is then needed to maintain the proper level to kill off germs. Additionally, pH profoundly affects what and how much chemical must be added to control the balance. A pH of between *7.2 – 7.6 is desirable in most cases.
*As one of the most important pool water balance and sanitation factors, pH should be checked hourly in most commercial pools. Even if you have an automatic chemical monitor/controller on your system, you need to double-check its readings with an independent pH test. With saltwater pools, pH level goes up fast, so you need to check it more often. Tests are available that require reagents and subjective evaluation of color depth and hue to judge their pH. But different users interpret these tests differently, and results can vary wildly.
Myron L’s POOLPRO™ gives instant lab-accurate, precise, easy-to-use, objective pH measurements, invaluable in correctly determining what and how much chemical to add to maintain water balance and effective sanitizer residuals.
Total Alkalinity (TA) is the sum of all the alkaline minerals in the water, primarily in bicarbonate form in swimming pools, but also as sodium, calcium, magnesium, and potassium carbonates and hydroxides, and affects pH directly through buffering. The greater the Total Alkalinity, the more stable the pH. *In general, TA should be maintained at 80 – 120 parts per million (ppm) for concrete pools to keep the pH stable. Maintaining a low TA not only causes pH bounce, but also corrosion and staining of pool walls and eye irritation. Maintaining a high TA causes over-stabilization of the water, creating high acid demands, formation of bicarbonate scale, and may result in the formation of white carbonate particles (suspended solids), which clouds the water. Reducing TA requires huge amounts of effort. So the best solution to TA problems is prevention through close monitoring and controlling. Myron L’s Alkalinity Test Kit comes with sodium hydrogen sulphate tablets and a mixing/measuring vial to determine alkalinity in parts per million.
The other water balance parameter pool professionals are most familiar with is Calcium Hardness (CH). CH is the calcium content of the water and is measured in parts per million. Low CH combined with a low pH and low TA significantly increases corrosivity of water. As the water becomes more aggressive, the solubility of calcium carbonate also increases. This means that plaster and marcite pool finishes will deteriorate quickly because calcium carbonate is a major component of both plaster and marcite. Low CH also leads to corrosion of metal components in the pool plant, particularly in heat exchangers. Calcium carbonate usually provides a protective film on the surface of copper heat exchangers and heat sinks. This thin layer prevents much water-to-metal interaction but does not adversely affect the heating process. Without this protective layer caused by low CH, heat exchangers and associated parts can be destroyed prematurely. Strangely enough, as water temperature increases, solubility of calcium carbonate decreases. *The recommended range for most pools is 200 – 400 ppm. Calcium hardness should be tested at least monthly and has the least significant effect on the water balance when compared to pH and TA.
Total Dissolved Solids (TDS) is the sum of all solids dissolved in water. If all the water in a swimming pool was allowed to evaporate, TDS would be what was left on the bottom of the pool – like the white deposits left in a boiling pot after all the water has evaporated. Some of this dissolved material includes hardness, alkalinity, cyanuric acid, chlorides, bromides, and algaecides. TDS also includes bather wastes, such as perspiration, urine, and others.
TDS is often confused with Total Suspended Solids (TSS). But TDS has no bearing on the turbidity, or cloudiness, of the water, as all the solids are truly in solution. It is TSS, or undissolved, suspended solids, present in or that precipitate out of the water that make the water cloudy.
High TDS levels do affect chlorine efficiency, algae growth, and aggressive water, but only minimally. TDS levels have the greatest bearing on bather comfort and water taste – a critical concern for commercial pool operators. At levels of over 5,000ppm, people can taste it. At over 10,000ppm bather towels are scratchy and mineral salts accumulate around the pool and equipment. Still some seawater pools comfortably operate with TDS levels of 32,000ppm or more.
As methods of sanitization have changed, high TDS levels have become more and more of a problem. *The best course of action is to monitor and control TDS by measuring levels and periodically draining and replacing some of your mature water with new, lower TDS tap water. This is a better option than waiting until you must drain and refill your pool, which is not allowed in some areas where water conservation is required by law. However, you can also decrease TDS with desalinization equipment as long as you compensate with Calcium Hardness. (Do not adjust water balance by moving pH beyond 7.8.)
Regardless, you do need to measure and compensate for TDS to get the most precise saturation index and adjust your pH and Calcium Hardness levels accordingly. *It is generally recommended that you adjust for TDS levels by subtracting one tenth of a saturation index unit (.1) for every 1,000ppm TDS over 1,000 to keep your water properly balanced. When TDS levels exceed 5,000ppm, it is recommended that you subtract half of a tenth, or one twentieth of unit (.05) per 1,000ppm. And as the TDS approaches that of seawater, the effect is negligible.
Hot tubs and spas have a more significant problem with TDS levels than pools. Because the swimmer load is relatively higher, more chemicals are added for super-chlorination and sudsing along with a higher concentration of bather wastes. The increased electrical conductance that high TDS water promotes can also result in electrolysis or galvanic corrosion. Every hot water pool operator should consider a TDS analyzer as a standard piece of equipment.
A TDS analyzer is required to balance the water of any pool or spa in the most precise way. Myron L’s POOLPRO and POOLMETER™ immediately display TDS levels to correctly calculate your water’s saturation index and to ensure you take corrective action before TDS gets out of hand.
Temperature is the last and least significant factor in maintaining water balance. As temperature increases, the water balance tends to become more basic and scale producing. Calcium carbonate becomes less soluble, causing it to precipitate out of solution. As temperature drops, water becomes more corrosive.
In addition to helping determine water balance, temperature also affects bather comfort, evaporation, chlorination, and algae growth (warmer temperatures encourage growth). Myron L’s POOLPRO also precisely measures temperature to one tenth of a degree at the same time any other parameter is measured.
The formula for determining water balance is called the Langlier Index, or Saturation Index. It is determined by the following formula:
SI= (pH + TF + CF + AF ) – 12.1
Where TF is the temperature, CF is Calcium Hardness, and AF is Total Alkalinity adjusted for temperature. 12.1 is the Total Dissolved Solids constant. Consult appropriate conversion charts to obtain the correct values for each variable.
– An index between -0.5 and +0.5 is acceptable pool water.
– An index of more than +0.5 is scale-forming.
– An index below -0.5 is corrosive.
pH, Total Alkalinity, and Calcium Hardness are the big three contributors to water balance. *Pool water will often be balanced if these factors are kept within the recommended ranges.
The most immediate concern of anyone monitoring and maintaining a pool is the effectiveness of the sanitizer – the germ-killer. There are many types of sanitizers, the most common being chlorine in swimming pools and bromine in hot tubs and spas. The effectiveness of the sanitizer is directly related to the pH and, to a lesser degree, the other factors influencing water balance.
To have true chemical control, you need to monitor both the sanitizer residual and the pH and use that information to chemically treat the water – that’s where ORP comes in. ORP indicates the ability of oxidizers to burn up organic matter in the water, which means your water is clean and sanitary. There are colorimetric tests used to determine the amount of effective sanitizer for chlorine and other elements, but none is as objective and precise in determining the total killing power of all sanitizers as ORP.
ORP stands for Oxidation Reduction Potential (or REDOX) of the water and is measured in millivolts (mV). The higher the ORP, the greater the killing power of all sanitizers, not just free chlorine, in the water. ORP is the only practical method available to monitor sanitizer effectiveness. Thus, every true system of automatic chemical control depends on ORP to work.
The required ORP for disinfection will vary slightly between disinfecting systems and is also dependent on the basic water supply potential, which must be assessed and taken into account when the control system is initialized. *650mV to 700 – 750mV is generally considered appropriate.
Electronic controllers can be inaccurate and inconsistent when confronted with certain unique water qualities, so it is critical to perform manual testing with separate instrumentation. *For automatic control dosing, it is generally recommended that you manually test pH and ORP prior to opening and then once during the day to confirm automatic readings.
*Samples for confirming automatic control dosing should be taken from a sample tap strategically located on the return line as close as possible to the probes in accordance with the manufacturer’s instructions. If manual and automatic readings consistently move further apart or closer together, you should investigate the reason for the difference.
ORP readings can only be obtained with an electronic instrument. Myron L’s POOLPRO provides the fastest, most precise, easy-to-use method of obtaining ORP readings to check the effectiveness of the sanitizer in any pool or spa. This is the best way to determine how safe your water is at any given moment.
A relatively new development, saltwater pools use regular salt, sodium chloride, to form chlorine with an electrical current much in the same way liquid bleach is made. As chlorine – the sanitizer – is made from the salt in the water, it is critical to maintain the salt concentration at the appropriate levels to produce an adequate level of sanitizer. It is even more important to test water parameters frequently in these types of pools and a spa, as saltwater does not have the ability to respond adequately to shock loadings (super-chlorination treatments).
Most saltwater chlorinators require a *2,500 – 3,000ppm salt concentration in the water (though some may require as high as 5,000-7,000ppm). This can barely be tasted, but provides enough salt for the system to produce the chlorine needed to sanitize the water.
(It is important to have a good stabilizer level – *30 – 50 ppm – in the pool, or the sunlight will burn up the chlorine. Without it, the saltwater system may not be able to keep up with the demand regardless of salt concentration.)
Taste and salt shortages are of little concern to seawater systems that maintain an average of 32,000ppm. In these high-salt environments, you need to beware of corrosion to system components that can distort salt level and other parameter readings.
Additionally, incorrect salt concentration readings can occur in any saltwater system. The monitoring/controlling components can and do fail or become scaled — sometimes giving a false low salt reading. Thus, you must test manually for salt concentration with separate instrumentation before adding salt.
You must also test salt concentration manually with separate instrumentation to re-calibrate your system. This is critical to system functioning and production of required chlorine. Myron L’s POOLPRO conveniently tests for salt concentration at the press of the button as a check against automatic controller systems that may have disabled equipment or need to be re-calibrated.
As you can see, there are many factors affecting the comfort and sanitation of pool and spa water and the functioning of the equipment and structures that hold it, and no one instrument or method can be used to determine ALL of them, but Myron L’s POOLPRO gives you the most precise and comprehensive water testing instrument in one easy-to-use, handheld waterproof unit. Where precision counts, we’ve got you covered.
RECORD KEEPING – What to do with all those measurements …
Now that you have the data, you have to correctly transcribe, evaluate, and report it to the proper government agencies, or at least archive it as permanent record of proper compliance to whatever regulations apply to your pool or spa. (As if sanitizing and balancing the chemistry of the water wasn’t enough.)
*It is recommended (by the World Health Organization and other entities) that data handling be done objectively and that data be recorded in a common format and in the most accurate way. Also, data should be stored in more than one permanent location and made available for future analysis. *Most municipalities require commercial aquatic facilities to keep permanent records onsite and available for inspection at any time.
*Myron L’s POOLPRO makes it easy to comply with data record requirements. The POOLPRO is an objective means to test ORP, pH, TDS, temperature and the mineral/salt content of any pool or spa. You just rinse and fill the cell cup by submerging the waterproof unit and press the button of the parameter you wish to measure. You immediately get a standard, numerical digital readout – no interpretation required – eliminating all subjectivity. Up to 100 date-time-stamped readings can be stored in memory and then later transferred directly to a computer using our BluDock™ accessory package. You just set the unit on the Bludock and download the data to the computer. The user never touches or tampers with the data, reducing the potential for human error in transcription. The data can then be imported into any program necessary for record-keeping and analysis. *The Bludock is the fastest, easiest, best way to keep records that comply with governing standards.
Myron L Company’s POOLPRO is SIMPLY the best.
*Consult your governing bodies for specific testing, chemical concentrations, and all other guidelines and requirements. The ranges suggested here are meant as general examples.
Myron L Company assumes no responsibility for lack of compliance to specific regulations governing the testing and control of parameters in your pool and/or spa.
TweetHow to maximize the life of your Myron L meter’s pH or pH/ORP sensor Your meter uses a general-purpose glass pH sensor. This glass sensor may be used in most applications. To ensure maximum life of your pH meter, read the following procedures. It is the experience of the repair technicians that 90% of all […]
How to maximize the life of your Myron L meter’s pH or pH/ORP sensor
Your meter uses a general-purpose glass pH sensor. This glass sensor may be used in most applications.
To ensure maximum life of your pH meter, read the following procedures. It is the experience of the repair technicians that 90% of all premature pH sensor failures can be prevented with a few maintenance procedures.
The following procedures should be performed after using your meter, or if you plan to store your meter for an extended period of time.
1. The pH sensor well (fig 1) must be filled with storage solution (preferred) or pH buffer 4, or tap water with table salt added and its protective cap (with foam insert) firmly installed.
Failure to do so will:
• Allow the glass membrane to dry out. A dehydrated glass membrane will not produce the necessary “Gel layer” on the sensor surface, which is essential to allow the exchange of hydrogen ions (measure pH).
• Allow airborne contaminants to settle on the glass membrane surface. Once contaminants dry onto the surface of the glass membrane, it will inhibit the transfer of hydrogen ions. (See factory approved cleaning process below.)
• Allow the reference junction to dry out. The reference junction material is usually a wick or fiber type material that completes the electrical circuit between the reference electrode cell and the solution being tested. Dehydration causes the reference solution to leach out of the electrode cavity, and form crystals in the junction. This is normally referred to as the “Bridging effect”.
Repeated dehydration of the pH or pH/ORP sensor will cause the instrument to have a slower response time, and be more difficult to calibrate. Dehydration will significantly reduce the normal service life of the sensor.
2. Store spare pH or pH/ORP sensors in a refrigerator. “Do not Freeze”. Take proper precautions not to allow the temperature to fall below freezing. This will cause the solution to expand and may damage the electrodes inside the sensor. Storage in a refrigerated environment will slow the evaporation of the storage solution, but not prevent evaporation. Always inspect and replace storage solution in spare sensor well on a regular basis.
Note: When using storage solution, it is common for white crystal formations to form around the seal of the pH sensor well and protective cap; this is a normal occurrence as the solution evaporates. Never store the sensor in high purity water (distilled or de-ionized).
Approved factory cleaning process for the pH sensor
During the normal use of your Myron L meter, you must clean your pH sensor bulb. The cleaning is necessary to eliminate the deposits of organic or inorganic contaminates left on the sensor from the solutions being tested. If you think your meter is inaccurate, or the display value drifts, or the response is slow and sluggish, perform the following tests.
Rinse the sensor well (three times) and fill with pH buffer 4 solution. If the pH continues to drift below the pH 4 level (i.e. 3, 2, or 1) repeat the test using buffer 10. If the pH level drifts beyond the pH level of 10 (i.e. 11, 12 etc.) the cleaning procedure outlined below may increase the performance and accuracy of your meter.
While performing the above tests, if the pH levels of the buffer solutions 4 and 10 actually drift towards pH 7, this is an indication that the pH sensor is damaged and needs to be replaced.
Caution: Wear proper eye protection and gloves during the following cleaning procedures.
Try the following to clean and recover the pH or pH/ORP sensors.
NOTE: Not all pH or pH/ORP sensors can be recovered.
1. Fill the pH/ORP sensor well with 100% Isopropyl alcohol. If not available use additive- free rubbing alcohol (70%). This will remove any oils.
2. Allow the sensor to soak for 10 minutes.
3. Rinse with RO or DI water.
4. Rinse the sensor well (three times) and fill
with storage or pH buffer 4 solution. Replace the protective cap and allow the sensor to recover overnight.
5. Re-calibrate the instrument according to the operations manual. If the instrument fails to calibrate properly, continue to the next step.
If the above procedure does not recover the pH sensor function, perform the following:
1. Fill the pH or pH/ORP sensor well with a hot salt solution 60°C (140°F) potassium chloride (KCI preferred) or hot tap water with table salt (NaCl). Allow the solution to cool.
2. Re-calibrate the instrument according to the operations manual. If the meter doesn’t calibrate properly, the pH or pH/ORP sensor must be replaced.
*CAUTION: If you do not use your Myron L meter on a regular basis, the storage solution in the pH or pH/ORP sensor well will evaporate over time and must be replenished. To prevent premature pH glass sensor failure, we suggest a preventative maintenance program. Failure to do so could void the factory warranty. The use of liquids containing high levels of solvents, such as acetone, xylene, and chlorinated hydrocarbons, or other harsh chemicals in your Myron L meter is not recommended.
Replacement pH sensor for Ultrameter II & Digital Dialysate Meters
Replacement pH sensor for Portable Analog pH Meters
Replacement pH sensor for Techpro II meters
Replacement pH Sensor PT2: RPT2
pH/ORP Sensor Storage Solutions: 32 oz
pH 4 Buffer: 32 oz
Video: Ultrameter II 6P pH Sensor (RPR) Replacement – MyronLMeters.com
Tweet Protect Your Ultrameter With Regular Maintenance When you spend a thousand bucks for a meter, you want it to last. That’s why you bought a Myron L meter in the first place. And, while Myron L meters are renowned for durability, they need care: cleaning, calibration, storage solution, sensor replacement, and sometimes repair. Keep […]
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.
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 MYRON L METERS
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 6PFCE Ultrameter II™, which can measure both ultrapure mixedbed 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.
Inline 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 Meters carries a variety of inline instruments, including resistivity Monitor/controllers 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.
The following table briefly covers recommended Myron L meters for Dl water applications.