Measuring ORP: MyronLMeters.com

Posted by 12 Apr, 2014

Tweet Ultrapen PT3 ORP tester Though the measurement of free chlorine concentration is often indicated for the disinfection of water and disinfectant byproduct control, there is a better way. Because free chlorine works through oxidation, ORP instrumentation can be used to monitor and control its effectiveness. ORP measures the actual oxidation power of the solution, […]




Ultrapen PT3 ORP tester Ultrapen PT3 ORP tester



Though the measurement of free chlorine concentration is often indicated for the disinfection of water and disinfectant byproduct control, there is a better way. Because free chlorine works through oxidation, ORP instrumentation can be used to monitor and control its effectiveness. ORP measures the actual oxidation power of the solution, specifically the strength and number of oxidation and reduction reactions in solution. This yields a clear picture of the efficacy of the chlorine present, regardless of the concentration or ratio of chlorine species in solution.
Measuring ORP directly reflects the sanitizing power of free chlorine or any other oxidizing or reducing chemicals. The measurement of ORP is precise, empirical and requires no user interpretation, making it ideal for water quality and industrial process control.
What is ORP?
ORP stands for Oxidation Reduction Potential, sometimes called REDOX. ORP is a differential measurement of the mV potentials built up when electrodes are exposed to solutions containing oxidants and reductants. ORP describes the net magnitude and direction of the flow of electrons between pairs of chemical species, called REDOX pairs.
In a REDOX pair, one chemical loses electrons while the other chemical gains electrons. The chemical in the REDOX exchange that acquires electrons is called the oxidant (HOCL, OCl-, ClO2, bromine, hydrogen peroxide, etc.). The chemical in the REDOX exchange that gives up electrons is called the reductant (Li, Mg2, Fe2+, Cr2, etc.). Oxidants acquire electrons through the process of reduction, i.e., they are reduced. Reductants lose their electrons through the process of oxidation, i.e., they become oxidized.
How is ORP measured?
ORP sensors are basically two electrochemical half-cells: A measurement electrode in contact with the solution being measured and a reference electrode in contact with a reservoir of highly concentrated salt solution.
When the solution being measured has a high concentration of oxidizers, it will accept more electrons than it loses so that the measurement electrode develops a higher electrical potential than the reference electrode. A voltmeter placed in line with the two electrodes will display this difference in potential between the two electrodes. Once the entire system reaches equilibrium, the resulting net potential difference represents the ORP. A positive reading indicates an oxidizing solution, and a negative reading indicates a reducing solution. The more positive or negative the value, the more powerful the oxidants or reductants, the greater their concentrations or both.
What does ORP measure?
ORP can be used to determine the efficacy of chemical disinfectants that work via the oxidation or reduction of the structures of microbial contaminants. For example, chlorine, an oxidant, will strip electrons from the negatively charged cell walls of some bacteria. Because ORP measures the total chemical activity of a solution, ORP measures the total efficacy all oxidizing and reducing disinfectants in solution: Hypochlorous acid, monochloramine, dichloramine, hypobromous acid, sodium hypochlorite, UV, ozone, peracetic acid, bromochlorodimethylhydantoin, etc.
ORP indicates the effectiveness of only those disinfectants that work through oxidation and reduction. ORP cannot be used to detect the presence of any one particular chemical or chemical species. Nor can it alone be used to determine the concentration of a known species of chemical in solution. This means that although ORP is the best way to know whether or not your sanitizer is working, it can’t tell you how much or what kind of sanitizer is working.
What factors affect ORP measurement?
While the accuracy of ORP sensors is relatively stable, which is why they do not require calibration, there are factors that affect their response time. Changes in temperature can affect response times by altering the kinetic rates of the reactions being measured, for example. Low temperatures reduce the kinetic rates and lengthen sensor response times.
The condition of the electrode will also alter response times by changing the “exchange current density” (the amount of electrons exchanged per unit area of exposed electrode). The lower the exchange current density, the more sluggish the sensor response. The typical measurement electrode is made from pure platinum (Pt) because it is a noble metal and, therefore, highly unreactive, i.e., the potential being measured is most likely due to the activity of the chemicals in the water and not reactions between the solution and the Pt itself. Even though Pt is a noble metal, it will form a thin oxide layer on the surface of the platinum when exposed to dissolved oxygen. This oxide layer facilitates the ORP measurement when it is very thin, one molecule thick, by attracting, or “adsorbing,” hydrolyzed oxidant or reductant molecules to the surface of the electrode.
Unfortunately, when the oxide layer becomes more than one molecule thick, the resulting lowered exchange current density offsets this benefit. Also, the adsorbed molecules cause a “memory effect.” If a sensor is placed in a less oxidizing solution after measuring a more oxidizing solution, it can take a very long time for the sensor to equilibrate to the new sample. Though the sensor response time is much slower, the final ORP reading will be the same.
ORP electrodes never require recalibration because there is no drift in zero point (as is the case with pH sensors). Any deviation from expected readings is most likely due to surface contamination of the electrodes or buildup of the oxide layer, both of which can easily be remedied by cleaning with a light abrasive, such as Softscrub®. Exposing the sensor to an “ORP conditioning solution” will help reduce the memory effect due to adsorption.
Can ORP be used as a surrogate parameter for free chlorine?
Yes. ORP measures the oxidizing power and, therefore, the actual residual sanitizing strength of the solution being tested. Simply counting how much chlorine is present is misleading because certain changes in water chemistry, such as pH or the addition of cyanuric acid, dramatically alter the oxidizing power of chlorine and, therefore, its efficacy, without changing how much chlorine is present.
When correlated with established disinfection control parameters, measurements and bacterial plate counts, this type of measurement gives a very accurate picture of the sanitizing activity. For this correlation to be valid, the water undergoing treatment must be characterized so that all chemical constituents are known. The pH and temperature values should be reported and held constant. ORP will report an empirical value or a hard number that indicates how active the sanitizer is. However, you have to make certain that microbial contamination is responding to the treatment. Once a correlation is established in a stable system, ORP is a very efficient and effective way to monitor microbial control.
ORP has long been used in bathing waters as the only means for automatic chemical dosing. In fact, the World Health Organization (WHO) suggests an ORP value of between 680-720 mV, depending on the sensor and the particular context, for safe bathing water. In the disinfection of drinking water, an ORP value of ~800 mV is required for oocyst inactivation.
For the purpose of pretreatment screening to detect chlorine levels prior to contact with chlorine-sensitive RO membranes, influent must first be screened to determine which chemicals besides chlorine are present that contribute to the ORP value. With these interferants characterized and pH and temperature held constant, ORP can be correlated to specific sanitizer concentrations, such as chlorine, in their known forms. Some manufacturers of RO membranes and other water quality treatment equipment will also specify an ORP tolerance value for prescreening and influent control. The same holds true of effluent screening.
Why ORP?
ORP is a faster, simpler empirical measurement than titration with DPD or other methods, and in many cases it gives the most accurate picture of the effect of all oxidizing and reducing chemicals in solution. No in-depth knowledge or training is required to obtain accurate repeatable results. User error is virtually eliminated because ORP readings require no subjective, visual interpretation, nor do they require calibration.
Using ORP disinfectant control can be automated because the measurement produces an electrical signal that can trigger switches when outside established control parameters. And ORP sensors are relatively low-maintenance. If you’re not using ORP to monitor and control chemical additions that work through REDOX, you should. You’ll save yourself time, hassle and money.
Myron L Meters is the premier internet retailer of accurate, reliable Myron L meters like the Ultrapen PT3, ORP pen tester.
Categories : Uncategorized

Measuring ORP: MyronLMeters.com

Posted by 12 Apr, 2014

Tweet Though the measurement of free chlorine concentration is often indicated for the disinfection of water and disinfectant byproduct control, there is a better way. Because free chlorine works through oxidation, ORP instrumentation can be used to monitor and control its effectiveness. ORP measures the actual oxidation power of the solution, specifically the strength and […]

Ultrapen PT3 ORP tester

Ultrapen PT3 ORP tester

Though the measurement of free chlorine concentration is often indicated for the disinfection of water and disinfectant byproduct control, there is a better way. Because free chlorine works through oxidation, ORP instrumentation can be used to monitor and control its effectiveness. ORP measures the actual oxidation power of the solution, specifically the strength and number of oxidation and reduction reactions in solution. This yields a clear picture of the efficacy of the chlorine present, regardless of the concentration or ratio of chlorine species in solution.
Measuring ORP directly reflects the sanitizing power of free chlorine or any other oxidizing or reducing chemicals. The measurement of ORP is precise, empirical and requires no user interpretation, making it ideal for water quality and industrial process control.
What is ORP?
ORP stands for Oxidation Reduction Potential, sometimes called REDOX. ORP is a differential measurement of the mV potentials built up when electrodes are exposed to solutions containing oxidants and reductants. ORP describes the net magnitude and direction of the flow of electrons between pairs of chemical species, called REDOX pairs.
In a REDOX pair, one chemical loses electrons while the other chemical gains electrons. The chemical in the REDOX exchange that acquires electrons is called the oxidant (HOCL, OCl-, ClO2, bromine, hydrogen peroxide, etc.). The chemical in the REDOX exchange that gives up electrons is called the reductant (Li, Mg2, Fe2+, Cr2, etc.). Oxidants acquire electrons through the process of reduction, i.e., they are reduced. Reductants lose their electrons through the process of oxidation, i.e., they become oxidized.
How is ORP measured?
ORP sensors are basically two electrochemical half-cells: A measurement electrode in contact with the solution being measured and a reference electrode in contact with a reservoir of highly concentrated salt solution.
When the solution being measured has a high concentration of oxidizers, it will accept more electrons than it loses so that the measurement electrode develops a higher electrical potential than the reference electrode. A voltmeter placed in line with the two electrodes will display this difference in potential between the two electrodes. Once the entire system reaches equilibrium, the resulting net potential difference represents the ORP. A positive reading indicates an oxidizing solution, and a negative reading indicates a reducing solution. The more positive or negative the value, the more powerful the oxidants or reductants, the greater their concentrations or both.
What does ORP measure?
ORP can be used to determine the efficacy of chemical disinfectants that work via the oxidation or reduction of the structures of microbial contaminants. For example, chlorine, an oxidant, will strip electrons from the negatively charged cell walls of some bacteria. Because ORP measures the total chemical activity of a solution, ORP measures the total efficacy all oxidizing and reducing disinfectants in solution: Hypochlorous acid, monochloramine, dichloramine, hypobromous acid, sodium hypochlorite, UV, ozone, peracetic acid, bromochlorodimethylhydantoin, etc.
ORP indicates the effectiveness of only those disinfectants that work through oxidation and reduction. ORP cannot be used to detect the presence of any one particular chemical or chemical species. Nor can it alone be used to determine the concentration of a known species of chemical in solution. This means that although ORP is the best way to know whether or not your sanitizer is working, it can’t tell you how much or what kind of sanitizer is working.
What factors affect ORP measurement?
While the accuracy of ORP sensors is relatively stable, which is why they do not require calibration, there are factors that affect their response time. Changes in temperature can affect response times by altering the kinetic rates of the reactions being measured, for example. Low temperatures reduce the kinetic rates and lengthen sensor response times.
The condition of the electrode will also alter response times by changing the “exchange current density” (the amount of electrons exchanged per unit area of exposed electrode). The lower the exchange current density, the more sluggish the sensor response. The typical measurement electrode is made from pure platinum (Pt) because it is a noble metal and, therefore, highly unreactive, i.e., the potential being measured is most likely due to the activity of the chemicals in the water and not reactions between the solution and the Pt itself. Even though Pt is a noble metal, it will form a thin oxide layer on the surface of the platinum when exposed to dissolved oxygen. This oxide layer facilitates the ORP measurement when it is very thin, one molecule thick, by attracting, or “adsorbing,” hydrolyzed oxidant or reductant molecules to the surface of the electrode.
Unfortunately, when the oxide layer becomes more than one molecule thick, the resulting lowered exchange current density offsets this benefit. Also, the adsorbed molecules cause a “memory effect.” If a sensor is placed in a less oxidizing solution after measuring a more oxidizing solution, it can take a very long time for the sensor to equilibrate to the new sample. Though the sensor response time is much slower, the final ORP reading will be the same.
ORP electrodes never require recalibration because there is no drift in zero point (as is the case with pH sensors). Any deviation from expected readings is most likely due to surface contamination of the electrodes or buildup of the oxide layer, both of which can easily be remedied by cleaning with a light abrasive, such as Softscrub®. Exposing the sensor to an “ORP conditioning solution” will help reduce the memory effect due to adsorption.
Can ORP be used as a surrogate parameter for free chlorine?
Yes. ORP measures the oxidizing power and, therefore, the actual residual sanitizing strength of the solution being tested. Simply counting how much chlorine is present is misleading because certain changes in water chemistry, such as pH or the addition of cyanuric acid, dramatically alter the oxidizing power of chlorine and, therefore, its efficacy, without changing how much chlorine is present.
When correlated with established disinfection control parameters, measurements and bacterial plate counts, this type of measurement gives a very accurate picture of the sanitizing activity. For this correlation to be valid, the water undergoing treatment must be characterized so that all chemical constituents are known. The pH and temperature values should be reported and held constant. ORP will report an empirical value or a hard number that indicates how active the sanitizer is. However, you have to make certain that microbial contamination is responding to the treatment. Once a correlation is established in a stable system, ORP is a very efficient and effective way to monitor microbial control.
ORP has long been used in bathing waters as the only means for automatic chemical dosing. In fact, the World Health Organization (WHO) suggests an ORP value of between 680-720 mV, depending on the sensor and the particular context, for safe bathing water. In the disinfection of drinking water, an ORP value of ~800 mV is required for oocyst inactivation.
For the purpose of pretreatment screening to detect chlorine levels prior to contact with chlorine-sensitive RO membranes, influent must first be screened to determine which chemicals besides chlorine are present that contribute to the ORP value. With these interferants characterized and pH and temperature held constant, ORP can be correlated to specific sanitizer concentrations, such as chlorine, in their known forms. Some manufacturers of RO membranes and other water quality treatment equipment will also specify an ORP tolerance value for prescreening and influent control. The same holds true of effluent screening.
Why ORP?
ORP is a faster, simpler empirical measurement than titration with DPD or other methods, and in many cases it gives the most accurate picture of the effect of all oxidizing and reducing chemicals in solution. No in-depth knowledge or training is required to obtain accurate repeatable results. User error is virtually eliminated because ORP readings require no subjective, visual interpretation, nor do they require calibration.
Using ORP disinfectant control can be automated because the measurement produces an electrical signal that can trigger switches when outside established control parameters. And ORP sensors are relatively low-maintenance. If you’re not using ORP to monitor and control chemical additions that work through REDOX, you should. You’ll save yourself time, hassle and money.
Myron L Meters is the premier internet retailer of accurate, reliable Myron L meters like the Ultrapen PT3, ORP pen tester.
Categories : Case Studies & Application Stories, Science and Industry Updates

Ultrapen PT3 ORP Pen Features: MyronLMeters.com

Posted by 4 Apr, 2014

Tweet                    The ULTRAPEN™ PT3 ORP Pen is designed to be extremely accurate, fast, and simple to use in diverse water quality applications. Advanced features include highly stable microprocessor-based circuitry; automatic temperature compensation from 15ºC to 30ºC while in calibration mode; user-intuitive design; and waterproof housing. A […]

 

DH-UP-PT3-2T

 

 

 

 

 

 

 

 

 

The ULTRAPEN™ PT3 ORP Pen is designed to be extremely accurate, fast, and simple to use in diverse water quality applications. Advanced features include highly stable microprocessor-based circuitry; automatic temperature compensation from 15ºC to 30ºC while in calibration mode; user-intuitive design; and waterproof housing. A true one-handed instrument, the PT3 is easy to calibrate and easy to use. To take a measurement, you simply push a button then dip the PT3 in solution. Results display in seconds.

FEATURES
1. Push Button — turns PT3 on; selects mode and unit of measurement preferences.
2. Battery Cap — provides access to battery for replacement.
3. Pocket Clip — holds PT3 to shirt pocket for secure storage.
4. Battery Indicator — indicates life remaining in battery.
5. Display — displays measurements, menu options, battery indicator, and
firmware revision (during power-up).
6. LED Indicator Light — indicates when to dip PT3 in solution, when measurement is in progress, and when to remove PT3 from solution.
7. ORP Sensor — measures oxidation-reduction potential or redox of solution.
8. Soaker Cap — contains a sponge soaked with Sensor Storage Solution to maintain sensor hydration. To remove, twist soaker cap while pulling off. To replace, fi soaker cap with storage solution just until sponge is covered. Squeeze and release tip of soaker cap so sponge will saturate with solution, then pour out any excess solution. Twist soaker cap while pushing back on.
CAUTION: Do NOT overfill the soaker cap as solution can squirt out while you are
pushing the cap back on.
9. Scoop — used to hold sample solution when dipping is not possible. To install, push scoop onto sensor while shifting side-to-side. To remove, pull scoop off while shifting side-to-side. Verify ORP sensor r
into PT3. If not, reinstall per ORP Sen page 5. To use, pour solution into scoop or hold scoop directly under a vertical stream to collect sample.
10. Holster — feed belt through strap in back of holster for hands-free portability.
11. Lanyard — attach through hole in top of pocket clip.
12. ORP Electrode Cleaning Paper — for deep cleaning the platinum electrode.

Technical Specs

ORP Range: -1000 mV to +1000 mV
ORP Accuracy: ± 10 mV
ORP Resolution: 1 mV ORP
Temperature Range: 0 – 71° C / 32 – 160° F
Temperature Accuracy: ± 0.1 ºC / ± 0.1 ºF
Temperature Resolution: 0.1ºC/0.1ºF
Time to Reading Stabilization: 10-45 seconds
Power Consumption: Active Mode 37 mA, Sleep Mode 2 μA
Temperature Compensation: Automatic In Calibration Mode From 15ºC to 30ºC
Physical Dimensions: 17,15 cm L x 1,59 cm D or 6.75 in. L x .625 in. D
Weight: 50,4 g / 1.78 oz. (without soaker cap and lanyard)
Case Material: Anodized Aircraft Aluminum with Protective Coating
Battery: One N type, Alkaline, 1.5V
Calibration Solutions: ORP80, ORP260, ORP470
Operating/Storage Temperature: 0 – 55ºC or 32 – 131ºF
Enclosure Ratings: IP67 and NEMA6
EN61236-1: 2006 – Annex A: 2008: Electrostatic discharge to the PT3 may cause it to spontaneously turn on. If this occurs, the PT3 will turn off.

* Temperature compensation in calibration mode: Temperature affects the reaction potentials for all chemicals differently. True ORP is the direct measurement of electron activity during an oxidation-reduction reaction, regardless of temperature. However, for maximum accuracy and ease of calibration, the Myron L Company has developed three calibration solutions with known dissolved species. We derived the temperature compensation (from 15ºC to 30ºC) for those solutions, and embedded automatic temperature compensation into the calibration function of your PT3. Note: To verify calibration while in measurement mode, you must manually correct for any variation in temperature. Example: @25ºC, ORP2602OZ calibration solution will read 260mV, however @ 20.0ºC ORP2602OZ will read 265mV.

MyronLMeters.com is the premier internet retailer of the Ultrapen PT3 and other reliable Myron L meters. Save 10% on Myron L meters when you order online HERE.

Categories : Product Updates

Conductivity Conversion to TDS in the Ultrameter: MyronLMeters.com

Posted by 1 Mar, 2014

TweetElectrical conductivity indicates solution concentration and ionization of the dissolved material. Since temperature greatly affects ionization, conductivity measurements are temperature dependent and are normally corrected to read what they would be at 25°C. A.           How It’s Done Once the effect of temperature is removed, the compensated conductivity is a function of the concentration (TDS). Temperature […]

Electrical conductivity indicates solution concentration and ionization of the dissolved material. Since temperature greatly affects ionization, conductivity measurements are temperature dependent and are normally corrected to read what they would be at 25°C.

A.           How It’s Done

Once the effect of temperature is removed, the compensated conductivity is a function of the concentration (TDS). Temperature compensation of the conductivity of a solution is performed automatically by the internal processor with data derived from chemical tables. Any dissolved salt at a known temperature has a known ratio of conductivity to concentration. Tables of conversion ratios referenced to 25°C have been published by chemists for decades.

B.           Solution Characteristics

Real world applications have to measure a wide range of materials and mixtures of electrolyte solutions. To address this problem, industrial users commonly use the characteristics of a standard material as a model for their solution, such as KCl, which is favored by chemists for its stability.

Users dealing with sea water, etc., use NaCl as the model for their concentration calculations. Users dealing with freshwater work with mixtures including sulfates, carbonates and chlorides, the three predominant components (anions) in freshwater that Myron L calls “Natural Water”. These are modeled in a mixture called “442™” which Myron L uses as a calibration standard, as it does standard KCl and NaCl solutions.

The Ultrameter II contains algorithms for these 3 most commonly referenced compounds. The solution type in use is displayed on the left. Besides KCl, NaCl, and 442, there is the User choice. The benefit of the User solution type is that one may enter the temperature compensation and TDS ratio by hand, greatly increasing accuracy of readings for a specific solution. That value remains a constant for all measurements and should be reset for different dilutions or temperatures.

C.           When does it make a lot of difference?

First, the accuracy of temperature compensation to 25°C determines the accuracy of any TDS conversion. Assume we have industrial process water to be pretreated by RO. Assume it is 45°C and reads 1500 µS uncompensated.

1.         If NaCl compensation is used, an instrument would report 1035 µS compensated, which corresponds to 510 ppm NaCl.

2.         If 442 compensation is used, an instrument would report 1024 µS compensated, which corresponds to 713 ppm 442.

The difference in values is 40%.

In spite of such large error, some users will continue to take data in the NaCl mode because their previous data gathering and process monitoring was done with an older NaCl referenced device.

Selecting the correct Solution Type on the Ultrameter II will allow the user to attain true TDS readings that correspond to evaporated weight.

If none of the 3 standard solutions apply, the User mode must be used.

TEMPERATURE COMPENSATION (Tempco) and TDS DERIVATION

The Ultrameter II contains internal algorithms for characteristics of the 3 most commonly referenced compounds. The solution type in use is displayed on the left. Besides KCl, NaCl, and 442, there is the User choice. The benefit of User mode is that one may enter the tempco and TDS conversion values of a unique solution via the keypad.

A. Conductivity Characteristics
When taking conductivity measurements, the Solution Selection determines the characteristic assumed as the instrument reports what a measured conductivity would be if it were at 25°C. The characteristic is represented by the tempco, expressed in %/°C. If a solution of 100 µS at 25°C increases to 122 µS at 35°C, then a 22% increase has occurred over this change of 10°C. The solution is then said to have a tempco of 2.2 %/°C. Tempco always varies among solutions because it is dependent on their individual ionization activity, temperature and concentration. This is why the Ultrameter II features mathematically generated models for known salt characteristics that also vary with concentration and temperature.

B. Finding the Tempco of an Unknown Solution

One may need to measure compensated conductivity of some solution unlike any of the 3 standard salts. In order to enter a custom fixed tempco for a limited measurement range, enter a specific value through the User function. The tempco can be determined by 2 different methods:

1. Heat or cool a sample of the solution to 25°C, and measure its conductivity. Heat or cool the solution to a typical temperature where it is normally measured. After selecting User function, set the tempco to 0 %/°C as in Disabling Temperature Compensation, pg. 15 (No compensation). Measure the new conductivity and the new temperature. Divide the % decrease or increase by the 25°C value. Divide that difference by the temperature difference.

2. Heat or cool a sample of the solution to 25°C, and measure its conductivity. Change the temperature to a typical measuring temperature. Set the tempco to an expected value as in User Programmable Temperature Compensation, pg. 15. See if the compensated value is the same as the 25°C value. If not, raise or lower the tempco and measure again until the 25°C value is read.

C. Finding the TDS Ratio of an Unknown Solution

Once the effect of temperature is removed, the compensated conductivity is a function of the concentration (TDS).

There is a ratio of TDS to compensated conductivity for any solution, which varies with concentration. The ratio is set during calibration in User mode as in User Programmable Conductivity to TDS Ratio, pg. 16.
A truly unknown solution has to have its TDS determined by evaporation and weighing. Then the solution whose TDS is now known can be measured for conductivity and the ratio calculated. Next time the same solution is to be measured, the ratio is known.

ph and ORP (6PFCE)

1. pH as an Indicator (6PFCE)

pH is the measurement of Acidity or Alkalinity of an aqueous solution. It is also stated as the Hydrogen Ion activity of a solution. pH measures the effective, not the total, acidity of a solution.
A 4% solution of acetic acid (pH 4, vinegar) can be quite palatable, but a 4% solution of sulfuric acid (pH 0) is a violent poison. pH provides the needed quantitative information by expressing the degree of activity of an acid or base. In a solution of one known component, pH will indicate concentration indirectly. However, very dilute solutions may be very slow reading, just because the very few ions take time to accumulate.

2. pH Units (6PFCE)

The acidity or alkalinity of a solution is a measurement of the relative availabilities of hydrogen (H+) and hydroxide (OH-) ions. An increase in (H+) ions increases acidity, while an increase in (OH-) ions increases alkalinity. The total concentration of ions is fixed as a characteristic of water, and balance would be 10-7 mol/liter (H+) and (OH-) ions in a neutral solution (where pH sensors give 0 voltage).
pH is defined as the negative logarithm of hydrogen ion concentration. Where (H+) concentration falls below 10-7, solutions are less acidic than neutral, and therefore are alkaline. A concentration of 10-9 mol/liter of (H+) would have 100 times less (H+) ions than (OH-) ions and be called an alkaline solution of pH 9.

3. The pH Sensor (6PFCE)

The active part of the pH sensor is a thin glass surface that is selectively receptive to hydrogen ions. Available hydrogen ions in a solution will accumulate on this surface and a charge will build up across the glass interface. The voltage can be measured with a very high impedance voltmeter circuit; the dilemma is how to connect the voltmeter to solution on each side.
The glass surface encloses a captured solution of potassium chloride holding an electrode of silver wire coated with silver chloride. This is the most inert connection possible from a metal to an electrolyte. It can
still produce an offset voltage, but using the same materials to connect to the solution on the other side of the membrane causes the 2 equal offsets to cancel.
The problem is, on the other side of the membrane is an unknown test solution, not potassium chloride. The outside electrode, also called the Reference Junction, is of the same construction with a porous plug in place of a glass barrier to allow the junction fluid to contact the test solution without significant migration of liquids through the plug material. Figure 33 shows a typical 2 component pair. Migration does occur, and this limits the lifetime of a pH junction from depletion of solution inside the reference junction or from contamination. The junction may be damaged if dried out because insoluble crystals may form in a layer, obstructing contact with test solutions.

Capture

Figure 33

 

Glass Surface

H+ ions

Junction plug
Platinum button

 

KCl solution

 

 

Glass

 

 

Electrode wires

 

 

 

4. The Myron L Integral pH Sensor (6PFCE)

The sensor in the Ultrameter II (see Figure 34) is a single construction in an easily replaceable package. The sensor body holds an oversize solution supply for long life. The reference junction “wick” is porous to provide a very stable, low permeable interface, and is located under the glass pH sensing electrode. This construction combines all the best features of any pH sensor known.

5. Sources of Error (6PFCE)

The most common sensor problem will be a clogged junction because a sensor was allowed to dry out. The symptom is a drift in the “zero” setting at 7 pH. This is why the Ultrameter II 6PFCE does not allow more than 1 pH unit of offset during calibration. At that point the junction is unreliable.

b. Sensitivity Problems

Sensitivity is the receptiveness of the glass surface. A film on the surface can diminish sensitivity and cause a long response time.

c. Temperature Compensation

pH sensor glass changes its sensitivity slightly with temperature, so the further from pH 7 one is, the more effect will be seen. A pH of 11 at 40°C would be off by 0.2 units. The Ultrameter II 6PFCE senses the sensor well temperature and compensates the reading.

B. ORP/Oxidation-Reduction Potential/REDOX (6PFCE)

1. ORP as an Indicator (6PFCE)

ORP is the measurement of the ratio of oxidizing activity to reducing activity in a solution. It is the potential of a solution to give up electrons (oxidize other things) or gain electrons (reduce).
Like acidity and alkalinity, the increase of one is at the expense of the other, so a single voltage is called the Oxidation-Reduction Potential, with a positive voltage showing, a solution wants to steal electrons (oxidizing agent). For instance, chlorinated water will show a positive ORP value.

2. ORP Units (6PFCE)

ORP is measured in millivolts, with no correction for solution temperature. Like pH, it is not a measurement of concentration directly, but of activity level. In a solution of only one active component, ORP indicates concentration. Also, as with pH, a very dilute solution will take time to accumulate a readable charge.

3. The ORP Sensor (6PFCE)
An ORP sensor uses a small platinum surface to accumulate charge without reacting chemically. That charge is measured relative to the solution, so the solution “ground” voltage comes from a reference junction – same as the pH sensor uses.

4. The Myron L ORP Sensor (6PFCE)

Figure 34, pg. 45, shows the platinum button in a glass sleeve. The same reference is used for both the pH and the ORP sensors. Both pH and ORP will indicate 0 for a neutral solution. Calibration at zero compensates for error in the reference junction. A zero calibration solution for ORP is not practical, so the Ultrameter II 6PFCE uses the offset value determined during calibration to 7 in pH calibration (pH 7 = 0 mV). Sensitivity of the ORP surface is fixed, so there is no gain adjustment either.

5. Sources of Error (6PFCE)

The basics are presented in pH and ORP, pg. 44, because sources of error are much the same as for pH. The junction side is the same, and though the platinum surface will not break like the glass pH surface, its protective glass sleeve can be broken. A surface film will slow the response time and diminish sensitivity. It can be cleaned off with detergent or acid, as with the pH glass.

C. Free Chlorine

1. Free Chlorine as an Indicator of Sanitizing Strength Chlorine, which kills bacteria by way of its power as an oxidizing agent, is the most popular germicide used in water treatment. Chlorine is not only used as a primary disinfectant, but also to establish a sufficient residual level of Free Available Chlorine (FAC) for ongoing disinfection.

FAC is the chlorine that remains after a certain amount is consumed by killing bacteria or reacting with other organic (ammonia, fecal matter) or inorganic (metals, dissolved CO2, Carbonates, etc) chemicals in solution. Measuring the amount of residual free chlorine in treated water is a well accepted method for determining its effectiveness in microbial control.

The Myron L  FCE method for measuring residual disinfecting power is based on ORP, the specific chemical attribute of chlorine (and other oxidizing germicides) that kills bacteria and microbes.

2. FCE Free Chlorine Units

The 6PIIFCE is the first handheld device to detect free chlorine directly, by measuring ORP. The ORP value is converted to a concentration reading (ppm) using a conversion table developed by Myron L Company through a series of experiments that precisely controlled chlorine levels and excluded interferants.

Other test methods typically rely on the user visually or digitally interpreting a color change resulting from an added reagent-dye. The reagent used radically alters the sample’s pH and converts the various chlorine species present into a single, easily measured species. This ignores the effect of changing pH on free chlorine effectiveness and disregards the fact that some chlorine species are better or worse sanitizers than others.

The Myron L 6PIIFCE avoids these pitfalls. The chemistry of the test sample is left unchanged from the source water. It accounts for the effect of pH on chlorine effectiveness by including pH in its calculation. For these reasons, the Ultrameter II’s FCE feature provides the best reading-to-reading picture of the rise and fall in sanitizing effectivity of free available chlorine.

The 6PIIFCE also avoids a common undesirable characteristic of other ORP-based methods by including a unique Predictive ORP value in its FCE calculation. This feature, based on a proprietary model for ORP sensor behavior, calculates a final stabilized ORP value in 1 to 2 minutes rather than the 10 to 15 minutes or more that is typically required for an ORP measurement.

The Myron L Ultrameter II 6PFCe is available at MyronLMeters.com, the premier internet retailer of Myron L products. Save 10% on the Myron L Ultrameter II6 PFCe when you order online here: http://www.myronlmeters.com/Myron-L-6P-Ultrameter-II-Multiparameter-Meter-p/dh-umii-6pii.htm

 

Categories : Application Advice, Technical Tips

ORP Applications – MyronLMeters.com

Posted by 26 Aug, 2013

TweetWHAT IS ORP? Oxidation Reduction Potential or Redox is the activity or strength of oxidizers and reducers in relation to their concentration. Oxidizers accept electrons, reducers lose electrons. Examples of oxidizers are: chlorine, hydrogen peroxide, bromine, ozone, and chlorine dioxide. Examples of reducers are sodium sulfite, sodium bisulfate and hydrogen sulfide. Like acidity and alkalinity, […]

WHAT IS ORP?

Oxidation Reduction Potential or Redox is the activity or strength of oxidizers and reducers in relation to their concentration. Oxidizers accept electrons, reducers lose electrons. Examples of oxidizers are: chlorine, hydrogen peroxide, bromine, ozone, and chlorine dioxide. Examples of reducers are sodium sulfite, sodium bisulfate and hydrogen sulfide. Like acidity and alkalinity, the increase of one is at the expense of the other.

A single voltage is called the Oxidation-Reduction Potential, where a positive voltage shows a solution attracting electrons (oxidizing agent). For instance, chlorinated water will show a positive ORP value whereas sodium sulfite (a reducing agent) loses electrons and will show a negative ORP value.

ORP is measured in millivolts (mV), with no correction for solution temperature. Like pH, it is not a measurement of concentration directly, but of activity level. In a solution of only one active component, ORP indicates concentration. As with pH, a very dilute solution will take time to accumulate a measurable charge.

An ORP sensor uses a small platinum surface to accumulate charge without reacting chemically. That charge is measured relative to the solution, so the solution “ground” voltage comes from the reference junction – the same type used by a pH sensor.

HISTORY OF ORP

ORP electrodes were first studied at Harvard University in 1936. These studies showed a strong correlation of ORP and bacterial activity. These tests were confirmed by studies on drinking water and swimming pools in other areas of the world. In 1971 ORP (700 mV) was adopted by the World Health Organization (WHO) as a standard for drinking water. In 1982 the German Standards Agency adopted the ORP (750 mV) for public pools and in 1988 the National Swimming Pool Institute adopted ORP (650 mV) for public spas.

WHERE IS ORP USED?
As you can tell by the previous paragraphs, ORP is used for drinking water, swimming pools and spas. However, ORP is also used for cooling tower disinfection, groundwater remediation, bleaching, cyanide destruction, chrome reductions, metal etching, fruit and vegetable disinfection and dechlorination.

In test after test on poliovirus, E. coli, and other organisms, a direct correlation between ORP and the rate of inactivation was determined. It is, therefore, possible to select an individual ORP value, expressed in millivolts, at which a predictable level of disinfection will be achieved and sustained regardless of variations in either oxidant demand or oxidant concentration. Thus, individual ORP targets, expressed in millivolts, can be determined for each application, which will result in completely reliable disinfection of pathogens, oxidation of organics, etc. Any level of oxidation for any purpose can be related to a single ORP number which, if maintained, will provide utterly consistent results at the lowest possible dosage.

WHY USE ORP?

ORP is a convenient measure of the oxidizer’s or reducer’s ability to perform a chemical task. ORP is not only valid over a wide pH range, but it is also a rugged electrochemical test, which can easily be accomplished using in-line and handheld instrumentation. It is by far a more consistent and reliable measurement than say chlorine alone.

LIMITATIONS FOR ORP
As with all testing, ORP has certain limitations. The speed of response is directly related to the exchange current density which is derived from concentration, the oxidation reduction system, and the electrode. If the ORP of a sample is similar to the ORP of the electrode, the speed will be diminished.

Carryover is also a possible problem when checking strong oxidizers or reducers, and rinsing well will help greatly.

Although a better indicator of bactericidal activity, ORP cannot be used as a direct indicator of the residual of an oxidizer due to the effect of pH and temperature on the reading. ORP can be correlated to a system by checking the oxidizer or reducer in a steady state system with a wet test, and measuring pH. If the system stays within the confines of this steady state parameter (usually maintained by in- line or continuous control), a good correlation can be made. The best recommendation for ORP is to use wet tests, and over three test periods correlate the ORP values to those test parameters.

FREE CHLORINE CONVERSION USING ORP

The most ubiquitous and cost-effective sanitizing agent used in disinfection systems is chlorine. When chlorine is used as the sanitizer, free chlorine measurements are required to ensure residual levels high enough for ongoing bactericidal activity. Myron L meters accurately convert ORP measurements to free chlorine based on the understanding of the concentrations of the forms of free chlorine at a given pH and temperature. The conversion is accurate when chlorine is the only oxidizing/reducing agent in solution and pH is stable between 5 and 9. This pH range fits most applications because pH is usually maintained such that the most effective form of free chlorine, hypochlorous acid, exists in the greatest concentration with respect to other variables such as human tolerance.

MYRON L METERS

Myron L offers a variety of handheld instruments and in-line Monitor/controllers that may be used to measure, monitor and/or control ORP. The latest is the Ultrapen PT3, ORP/Redox and Temperature Pen. The Ultrameter III™ 9PTKA, Ultrameter II™ 6PFCE, PoolPro™ PS6FCE and PS9TK, and D-6 Digital Dialysate Meter™ are multi-parameter handheld instruments with ORP and FCE free chlorine measuring capabilities. These instruments also have the capability to measure conductivity, TDS, resistivity, pH, mineral/salt concentration and temperature, making them the preferred instruments for all water treatment professionals. The 720 Series II Monitor/controllers are an excellent choice for continuous in-line measurements.

For additional information, visit us at MyronLMeters.com.

Categories : Case Studies & Application Stories, Science and Industry Updates

The Ultrameter III 9PTKA: MyronLMeters.com

Posted by 12 Jun, 2013

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Categories : Product Updates, Uncategorized

The Ultrameter II 6P: MyronLMeters.com

Posted by 12 Jun, 2013

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Categories : Product Updates

The Ultrapen PT-3: MyronLMeters.com

Posted by 12 Jun, 2013

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Categories : Product Updates

ORP Measurements and ORP Meters

Posted by 28 Dec, 2010

TweetWhat is the ORP of water? ORP stands for Oxidation Reduction Potential, also known as Redox. It is a measure of the tendency of a chemical species to acquire electrons and thereby be reduced. The ORP measurement is displayed in millivolts (mV) and the usual range for ORP meters is (+1000 mV) to (-1000 mV) […]

What is the ORP of water?

ORP stands for Oxidation Reduction Potential, also known as Redox. It is a measure of the tendency of a chemical species to acquire electrons and thereby be reduced. The ORP measurement is displayed in millivolts (mV) and the usual range for ORP meters is (+1000 mV) to (-1000 mV) with no temperature compensation. It is not a direct measurement of concentration, but rather an indicator of the activity level or strength of an oxidizer or reducer.

An oxidizer gains electrons, while a reducer loses electrons. Examples of oxidizers are: chlorine, hydrogen peroxide, bromine, ozone, and chlorine dioxide. Examples of reducers are sodium sulfite, sodium bisulfate and hydrogen sulfide. Like acidity and alkalinity, the increase of one is at the expense of the other.

When measuring with an ORP meter, a positive voltage shows a solution gaining electrons (oxidizing) and a negative voltage shows a solution losing electrons (reducing). For instance, chlorinated water will show a positive ORP value and a solution with sodium sulfite will have a negative ORP value.

ORP Applications

ORP meters are used for swimming pools and spas, drinking water, cooling tower disinfection, and groundwater remediation. ORP meters are also crucial for bleaching applications, cyanide destruction, chrome reductions, metal etching, fruit and vegetable disinfection and dechlorination.

Many organizations around the world have accepted ORP as a standard for disinfection. An ORP of 750 mV was adopted by the German Standards Agency in 1982 for public pools. The National Swimming Pool Institute also adopted an ORP of 650 mV for public spas. The World Health Organization (WHO) adopted an ORP of 700 mV as a standard for drinking water.

How to use ORP?

Oxidation Reduction Potential is a convenient measure of the oxidizer’s or reducer’s ability to perform a chemical task. It is a more consistent and reliable measurement than chlorine alone. You can establish an ORP measurement at which acceptable sanitation is achieved and maintained for your application by testing the rate of inactivation of various microorganisms. There are published standards for many applications or a lab water analysis should be able to provide these results if necessary. For example, the above paragraph mentions the 750 mV standard for public swimming pools. Once that has been determined you can use an ORP controller to maintain that level of sanitation.

ORP Limitations

Similar to pH, high purity solutions will take extra time to stabilize a reading due to the low ionic strength. Also, if the ORP measurement of a sample solution is similar to the mV of the ORP probe, it will take slightly longer for a reading to respond and stabilize. Rinsing the probe with a strong oxidizer will help to increase the reaction time and give accurate readings quickly. Ensure that there is not residual solution in the ORP probe by rinsing thoroughly with the solution to be tested.

ORP measuements

ORP meters like the 728II are used to monitor the sanitizer level. A pH controller, such as the 723II, is also used to monitor pH. The controllers automatically turn the appropriate chemical feeders on and off, as required to maintain the proper sanitizer and pH levels. This results in good water quality and elimination of chloramines and other unpleasant contaminants, as well as in savings in chemical and labor.

Generally, ORP meters without pH control should not be used with alkaline sanitizers such as sodium hypochlorite or calcium hypochlorite. If the pH remains fairly constant, these inexpensive controllers provide a very cost effective solution to the problem of chemical control in small commercial applications.

Other handheld instruments like the POOLPRO PS6 have been designed to test ORP reliably for swimming pools and other applications. If you are in the medical dialysis industry, you will definitely be interested in the Digital Dialysate Meter D-6 that test ORP, among other parameters.

Categories : Technical Tips