TweetWater Quality Parameters Measuring Key Water Quality Parameters The right meter is essential for measuring any of several key water quality parameters: Conductivity is the ability of water to conduct an electrical current and is an indirect measure of the conductive ionic mineral concentration. The more conductive ions that are present, the more electricity can be […]
Water Quality Parameters
The right meter is essential for measuring any of several key water quality parameters:
Conductivity is the ability of water to conduct an electrical current and is an indirect measure of the conductive ionic mineral concentration. The more conductive ions that are present, the more electricity can be conducted by the water. This measurement is expressed in microsiemens per centimeter (ÂµS/cm) at 25Âº Celsius. Myron L Meters carries a complete line of conductivity meters, including the Ultrameter II 4P.
Resistivity is the inverse of conductivity. Electrical conductivity is a measure of waterâ€™s resistance to an electric current. Water itself has a weak electrical conductivity. Electric current is transported in water by dissolved ions, making conductivity measurement a quick and reliable way to monitor the total amount of ionic contaminants in water. Myron L Meters carries a complete line of resistivity meters, including inline monitor/controllers like the 753II Resistivity Digital Monitor/Controller. Read more about Measuring Key Water Quality Parameters
The Ultrameter III 9P is the most comprehensive water meter on the market, measuring 9 parameters with a single instrument: Conductivity, Resistivity, TDS, Alkalinity, Hardness, Langelier Saturation Index,
ORP/Free Chlorine, pH, Temperature. Three parameters – LSI, hardness, and alkalinity require titration. Find out more about the Ultrameter III 9P
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TweetThe right meter is essential for measuring any of several key water quality parameters: Conductivity is the ability of water to conduct an electrical current and is an indirect measure of the conductive ionic mineral concentration. The more conductive ions that are present, the more electricity can be conducted by the water. This measurement is […]
The right meter is essential for measuring any of several key water quality parameters:
Conductivity is the ability of water to conduct an electrical current and is an indirect measure of the conductive ionic mineral concentration. The more conductive ions that are present, the more electricity can be conducted by the water. This measurement is expressed in microsiemens per centimeter (µS/cm) at 25º Celsius. Myron L Meters carries a complete line of conductivity meters, including the Ultrameter II 4P.
Resistivity is the inverse of conductivity. Electrical conductivity is a measure of water’s resistance to an electric current. Water itself has a weak electrical conductivity. Electric current is transported in water by dissolved ions, making conductivity measurement a quick and reliable way to monitor the total amount of ionic contaminants in water. Myron L Meters carries a complete line of resistivity meters, including inline monitor/controllers like the 753II Resistivity Digital Monitor/Controller.
Total Dissolved Solids (TDS) is also a measurement of the amount of dissolved minerals in the water. In this instance they would be called solids in solution. The quantity of dissolved solids in the solution is directly proportional to the conductivity. In this case, conductivity is the measurement but it is used to estimate TDS. It is measured with a conductivity meter but is reported as TDS in parts per million (ppm), via a complex algorithm. Myron L Meters carries a complete line of TDS meters, including the Ultrapen PT1.
pH is a measure of the concentration of hydrogen ions in the water, indicating the acidity or alkalinity of the water. On the pH scale of 0-14, a reading of 7 is considered to be neutral. Readings below 7 indicate acidic conditions, while readings above 7 indicate the water is alkaline or basic. Naturally occurring fresh waters have a pH range between 6 and 8. Myron L Meters carries a complete line of pH meters, including the Ultrapen PT2
Temperature is expressed in degrees Celsius (C) or Fahrenheit (F). Most digital handheld Myron L Meters include a temperature function.
Oxidation reduction potential (ORP)can correlate millivolt readings to the sanitization strength of the water. Microbes can cause corrosion, fouling, and disease, and oxidizing biocides are usually used to keep microbial levels under control. ORP is expressed in millivolts (mV). Myron L Meters carries a complete line of ORP meters, including the Ultrapen PT3
Free Chlorine refers to both hypochlorous acid (HOCl) and the hypochlorite (OCl–) ion or bleach, and is commonly added to water systems for disinfection. Free chlorine is typically measured in drinking water disinfection systems to find whether the water system contains enough disinfectant. Myron L Meters Ultrameter II 6PFCe and Ultrapen PT4 can both be used to measure free chlorine.
Salinity is simply a measure of the amount of salts dissolved in water, a measurement useful to pool service technicians and others. You can measure salinity with a Myron L Pool Pro PS6.
Alkalinity is a measure of the capacity of water or any solution to neutralize or “buffer” acids. This measure of acid-neutralizing capacity is important in figuring out how “buffered” the water is against sudden changes in pH. Alkalinity is a titration function of the Ultrameter III 9PTKA.
Hardness is caused by compounds of calcium and magnesium, and by a variety of other metals. As water moves through soil and rock, it dissolves very small amounts of minerals and holds them in solution. Calcium and magnesium dissolved in water are the two most common minerals that make water “hard.” Hardness is a titration function of the Ultrameter III 9PTKA.
LSI or Langelier Saturation Index helps you determine the scaling potential of water. LSI is a calculated number used to predict the calcium carbonate stability of water. It indicates whether the water will precipitate, dissolve, or be in equilibrium with calcium carbonate. LSI is a titration function of the Ultrameter III 9PTKA.
MyronLMeters.com is the premier internet retailer of accurate, reliable Myron L meters. Save 10% when you order Myron L meters online at MyronLMeters.com. You’ll find reliable instruments for every water quality parameter mentioned above.
Tweet how to maintain and clean free chlorine sensor for the ultrapen pt4 Ultrapen PT4 Free Chlorine Pen MAINTENANCEI. Routine Maintenance1. ALWAYS rinse the FCE sensor with clean water after each use.2. ALWAYS replace the soaker cap half filled with Sensor Storage Solution to prevent thesensor from drying out after each use.3. Do not drop, […]
MAINTENANCEI. Routine Maintenance1. ALWAYS rinse the FCE sensor with clean water after each use.2. ALWAYS replace the soaker cap half filled with Sensor Storage Solution to prevent thesensor from drying out after each use.3. Do not drop, throw, or otherwise strike the PT4. This voids the warranty.4. Do not store the PT4 in a location where the ambient temperatures exceed its specified Operating/Storage Temperature limits.
II. Battery Replacement The PT4 display has a battery indicator that depicts the liferemaining in the battery. When the indicator icon is at 3 bars, the battery is full. When the indicator icon falls to 1 bar, replace the battery with an N type battery.
1. In a clean/dry environment, unscrew the pen cap in a counter-clockwise motion.2. Slide the cap and battery housing out of the PT4.3. Remove the depleted battery out of its housing.4. Insert a new battery into the battery housing oriented with the negative end touching the spring.5. Align the groove along the battery housing with the guide bump inside the PT4case and slide the battery housing back in.6. Screw the PT4 cap back on in a clockwise direction. Do not over tighten.
III. Sensor Cleaning (additional sensor cleaning methods at www.myronl.com) Cleaning the sensor: The Myron L Company recommends cleaning your sensor every two weeks, however this depends on application and frequency of use. Indications of a dirty sensor are slower and/or erroneous readings.There are three critical components in your PT4 sensor; a very sensitive glass pH sensor bulb, a platinum ORP electrode, and a temperature sensor encapsulated in a small glass noid. Use extreme caution when cleaning your PT4 sensor.To clean your sensor, select one of the following methods:• Basic Cleaning: Using a solution made of dish soap mixed with water and a cotton swab, gently clean the inside of the sensor body and platinum electrode, rinse thoroughly with clean water, then recondition the sensor.• Cleaning the pH Sensor Bulb: If the sensor becomes dirty, clean the sensor surface with an isopropyl soaked cotton swab. Then rinse thoroughly with clean water.• Deep cleaning the platinum ORP electrode: Using the ORP electrode cleaning paper and water, gently clean the platinum electrode, rinse thoroughly then recondition the sensor.To recondition the sensor: Rinse the sensor thoroughly with clean water, then allow it to soak in Storage Solution for a minimum of 1 hour (for best results allow the sensor to soak in Storage Solution overnight).
IV. FCE Sensor ReplacementCAUTION: Only Remove/Replace the FCE sensor in a CLEAN and DRYenvironment!To remove the FCE sensor: Remove the soaker cap; make sure the PT4 (including the FCE sensor) is clean and dry.Loosen the battery tray (to allow pressure equalization).Then firmly grasp the FCE sensor body and slowly pull the FCE sensor out.To install a new FCE sensor: Line up the alignment tabs on the FCE sensor with the alignment slots on the PT4 unit. Gently push the FCE sensor into position, then close the battery cap.
You will need: RPT4 Replacement FCE Sensor (with instructions)
TweetUltrapen PT4 Free Chlorine Pen MAINTENANCE I. Routine Maintenance 1. ALWAYS rinse the FCE sensor with clean water after each use. 2. ALWAYS replace the soaker cap half filled with Sensor Storage Solution to prevent the sensor from drying out after each use. 3. Do not drop, throw, or otherwise strike the PT4. This voids […]
I. Routine Maintenance
1. ALWAYS rinse the FCE sensor with clean water after each use.
2. ALWAYS replace the soaker cap half filled with Sensor Storage Solution to prevent the
sensor from drying out after each use.
3. Do not drop, throw, or otherwise strike the PT4. This voids the warranty.
4. Do not store the PT4 in a location where the ambient temperatures exceed its specified Operating/Storage Temperature limits.
II. Battery Replacement The PT4 display has a battery indicator that depicts the life
remaining in the battery. When the indicator icon is at 3 bars, the battery is full. When the indicator icon falls to 1 bar, replace the battery with an N type battery.
1. In a clean/dry environment, unscrew the pen cap in a counter-clockwise motion.
2. Slide the cap and battery housing out of the PT4.
3. Remove the depleted battery out of its housing.
4. Insert a new battery into the battery housing oriented with the negative end touching the spring.
5. Align the groove along the battery housing with the guide bump inside the PT4
case and slide the battery housing back in.
6. Screw the PT4 cap back on in a clockwise direction. Do not over tighten.
III. Sensor Cleaning (additional sensor cleaning methods at www.myronl.com) Cleaning the sensor: The Myron L Company recommends cleaning your sensor every two weeks, however this depends on application and frequency of use. Indications of a dirty sensor are slower and/or erroneous readings.
There are three critical components in your PT4 sensor; a very sensitive glass pH sensor bulb, a platinum ORP electrode, and a temperature sensor encapsulated in a small glass noid. Use extreme caution when cleaning your PT4 sensor.
To clean your sensor, select one of the following methods:
• Basic Cleaning: Using a solution made of dish soap mixed with water and a cotton swab, gently clean the inside of the sensor body and platinum electrode, rinse thoroughly with clean water, then recondition the sensor.
• Cleaning the pH Sensor Bulb: If the sensor becomes dirty, clean the sensor surface with an isopropyl soaked cotton swab. Then rinse thoroughly with clean water.
• Deep cleaning the platinum ORP electrode: Using the ORP electrode cleaning paper and water, gently clean the platinum electrode, rinse thoroughly then recondition the sensor.
To recondition the sensor: Rinse the sensor thoroughly with clean water, then allow it to soak in Storage Solution for a minimum of 1 hour (for best results allow the sensor to soak in Storage Solution overnight).
IV. FCE Sensor Replacement
CAUTION: Only Remove/Replace the FCE sensor in a CLEAN and DRY
To remove the FCE sensor: Remove the soaker cap; make sure the PT4 (including the FCE sensor) is clean and dry.
Loosen the battery tray (to allow pressure equalization).
Then firmly grasp the FCE sensor body and slowly pull the FCE sensor out.
To install a new FCE sensor: Line up the alignment tabs on the FCE sensor with the alignment slots on the PT4 unit. Gently push the FCE sensor into position, then close the battery cap.
You will need: RPT4 Replacement FCE Sensor (with instructions)
TweetIV. Calibration of the Ultrapen PT4 Free Chlorine Pen The manufacturer recommends calibrating twice a month, depending on usage. However, you should check the calibration whenever measurements are not as expected. For greatest accuracy, you should perform a 3-point wet pH calibration, and wet ORP calibration with the ORP Standard Solution closest in value to […]
IV. Calibration of the Ultrapen PT4 Free Chlorine Pen
The manufacturer recommends calibrating twice a month, depending on usage.
However, you should check the calibration whenever measurements are not as expected. For greatest accuracy, you should perform a 3-point wet pH calibration, and wet ORP calibration with the ORP Standard Solution closest in value to the solution you will be testing.
NOTE: If the measurement is NOT within calibration limits for any reason, “Error” will display. Check to make sure you are using a proper Myron L Company pH Buffer or ORP Standard Solution. If the solution is correct, clean the sensor as described in Sensor Cleaning section on page 4 of the operations manual. Restart calibration.
NOTE: Small bubbles trapped in the sensor may give a false calibration. After calibration is completed, measure the pH Buffer or ORP Standard Solutions again in solution check mode “SOL ck” (see pages 3 and 4 of the operations manual) to verify correct calibration.
NOTE: If at any point during calibration, you do not submerge the sensor in solution before the flashing slows, allow the PT4 to power off and start over.
NOTE: You should always calibrate with pH 7 first.
A. Calibration preparation
For maximum accuracy, fill 2 clean containers with each pH Buffer and/or ORP Standard Solution. Arrange them in such a way that you can clearly remember which is the rinse solution and which is the calibration standard/buffer. If you don’t have enough standard/ buffer, you can use 1 container of each standard/buffer for calibration and 1 container of clean water for all rinsing. Always rinse the FCE sensor between standard/buffer solutions. Ensure the FCE sensor is clean and free of debris.
B. pH Calibration using pH 7, 4, and 10 Buffer Solutions.
NOTE: You should always calibrate with pH 7 first.
1. Thoroughly rinse the PT4 by submerging the sensor in pH 7 Buffer rinse solution and swirling it around.
2. Push and release the push button to turn the PT4 on.
3. Push and hold the push button. The display will alternate between “CAL”, “FAC CAL”, “ºCºF TEMP”, “ModE SEL”, “PAr SEL”, “SOL ck”, and “ESC”.
4. Release the button when “CAL” displays.
5. The display will alternate between “PUSHnHLD” and “CAL.
6. Push and hold the button, The display will alternate between “PH” and “ORP”.
7. Release the button when “PH” is displayed.
8. The display will indicate “CAL” and the LED will flash rapidly.
9. While the LED flashes rapidly, dip the PT4 in pH 7 Buffer Calibration Solution so that the sensor is completely submerged.
10. While the LED flashes slowly, the pH calibration point will display along with “CAL”.
Swirl the PT4 around to remove bubbles, keeping the sensor submerged.
11. If the pH 7 calibration is successful, the display will indicate “SAVEd”, then “PUSHCONT” will be displayed (“PUSHCONT” will NOT be displayed if only calibrated with pH 4 or 10).
12. Push and release to continue or let the unit time out to exit after a 1-point or 2-point calibration.
13. Repeat steps 9 through 12 with pH 4 and 10 Buffer Solutions. After the 3rd calibration point is successfully saved, the display will indicate “SAVEd” and power off.
14. Verify calibration by retesting the calibration solution in solution check mode “SOL ck”, see section V below.
C. ORP Calibration using 80mV Quinhydrone, 260mV Quinhydrone, or 470mV MLC Light’s ORP Standard Solution.
NOTE: The PT4 has automatic temperature compensation in ORP calibration mode (from 15ºC to 30ºC).
1. Follow pH calibration steps 1 through 6, using ORP Solutions.
2. Release the button when “ORP” is displayed.
3. The display will indicate “CAL” and the LED will flash rapidly.
4. While the LED flashes rapidly, dip the PT4 in ORP Standard Solution so that the
sensor is completely submerged.
5. While the LED flashes slowly, the ORP calibration point will display along with “CAL”.
Swirl the PT4 around to remove any air bubbles, keeping the sensor submerged.
6. If the ORP calibration is successful, the display will indicate “CAL SAVEd”, then time out.
7. Verify calibration by retesting the calibration solution in solution check mode.
V. SOLUTION CHECK
Solution check is provided to verify the proper calibration value was recorded when using pH Buffers and ORP Standard Solutions. To verify proper calibration, simply put the PT4 into solution check mode, select the mode to verify (pH or ORP), then dip the sensor into the pH Buffer or ORP Calibration Solution so that the sensor is completely submerged and swirl around to release any air bubbles, then verify displayed value matches the value on the bottle.
To perform Solution Check:
1. Push and release the push button to turn the PT4 on.
2. Push and hold the push button. The display will alternate between “CAL”, “FAC CAL”, “ºCºF TEMP”, “ModE SEL”, “PAr SEL”, “SOL ck”, and “ESC”.
3. Release the button when “SOL ck” displays.
4. The display will alternate between “PUSHnHLD” and “SOL ck”.
5. Push and hold the button, The display will alternate between “PH” and “ORP”.
6. Release the button when desired mode (pH or ORP) is displayed.
7. While the LED flashes rapidly, dip the PT4 in FRESH buffer/calibration solution so that the sensor is completely submerged and swirl the PT4 around to remove any air bubbles.
8. Verify value displayed is correct.
NOTE: To verify ORP calibration while in solution check mode, you must manually correct for temperature variations from 25ºC. See instructions that come with the ORP Standard Solutions for temperature chart.
VI. Factory Calibration
When pH Buffers are not available, the PT4 can be returned to factory default calibration using the FAC CAL function. This will erase any stored wet calibration.
NOTE: Default factory calibration resets the electronics only and does NOT take the condition of the sensor into consideration.
To return your PT4 to factory calibration:
1. Push and release the push button.
2. Push and hold the button. The display will alternate between “CAL”, “FAC CAL”, “ºCºF TEMP”, “ModE SEL”, “PAr SEL”, “SOL ck”, and “ESC”.
3. Release the button when “FAC CAL” displays. The display will alternate between “PUSHnHLD” and “FAC CAL”.
4. Push and hold the push button. “SAVEd FAC” displays indicating the pen has been reset to its factory calibration.
TweetOPERATING INSTRUCTIONS Ultrapen PT4 Free Chlorine Pen NOTE: Selecting “ESC” from any menu immediately powers the PT4 off without saving changes. I. Temperature Unit Selection The PT4 allows you to select the type of units used for displaying temperature: ˚C (Degrees Celsius) or ˚F (Degrees Fahrenheit). To set the preference: 1. Push and release the push […]
OPERATING INSTRUCTIONS Ultrapen PT4 Free Chlorine Pen
NOTE: Selecting “ESC” from any menu immediately powers the PT4 off without saving changes.
I. Temperature Unit Selection
The PT4 allows you to select the type of units used for displaying temperature:
˚C (Degrees Celsius) or ˚F (Degrees Fahrenheit).
To set the preference:
1. Push and release the push button to turn the PT4 on.
2. Push and hold the button. The display will alternate between “CAL”, “FAC CAL”, “ºCºF TEMP”, “ModE SEL”, “PAr SEL”, “SOL ck”, and “ESC”.
3. Release the button while “ºCºF TEMP” is displayed. The display will alternate between “PUSHnHLD” and “ºCºF TEMP”.
4. Push and hold the button. The display will alternate between “˚C”, “˚F” and “ESC”.
Release the button when desired unit preference displays.
5. “SAVEd ºC” or “SAVEd ºF” will display; then the unit will power off.
II. FCE Mode Selection
The PT4 allows you to select the FCE measurement mode you prefer:
Hold Mode (default) — will display real-time readings until stable or 2 minutes, which ever
comes fi then display fi readings.
LIVE Mode — real-time readings are displayed continuously for up to 5 minutes, a push and release of the button will turn your PT4 off immediately.
To set the FCE measurement mode preference:
1. Push and release the push button to turn the PT4 on.
2. Push and hold the button. The display will alternate between “CAL”, “FAC CAL”, “ºCºF TEMP”, “ModE SEL”, “PAr SEL”, “SOL ck”, and “ESC”.
3. Release the button when “ModE SEL” is displayed. The display will alternate between “PUSHnHLD” and “ModE SEL”.
4. Push and hold the push button. The display will alternate between “Hold”, “LIVE” and “ESC”.
5. Release the button when desired mode displays.
6. “SAVEd” will display, then the PT4 will power off.
III. FCE Measurement
The following table explains what the LED Indicator Light signals indicate and gives the duration of each signal:
CAUTION: To measure solution at the extremes of the specified temperature or FCE range, allow the PT4 to equilibrate by submerging the sensor in the sample solution for 1 minute prior to taking a measurement.
NOTE: If you cannot dip the PT4 in the sample solution, pour the sample into a clean container. If you don’t have a container or need to test a vertical stream of solution, use the scoop to hold sample solution.
1. Rinse the pen 3 times in a sample of the solution.
2. Push and release the push button.
3. While the LED flashes rapidly, dip the PT4 in FRESH sample solution so that the sensor is completely submerged. If you do not submerge the sensor in solution before the flashing slows, allow the PT4 to power off and retake the reading.
4. While the LED flashes slowly, swirl the PT4 around to remove any air bubbles, keeping the sensor submerged.
a. In Hold mode when the LED turns on solid, remove the PT4 from solution. The display will alternate between the final FCE and temperature readings. Note the readings for your records.
b. In LIVE mode allow the PT4 to remain in solution while the LED flashes slowly. The display will alternate between live FCE and temperature readings. Note the readings for your records. LIVE measurement will time out after 5 minutes OR push and release the push button to turn the PT4 off at any time during LIVE measurement.
TweetThe Myron L ULTRAPEN™ PT4 Free Chlorine Pen is designed to be extremely accurate, fast, and simple to use in diverse water quality applications. Advanced features include automatic temperature compensation in calibration mode; highly stable microprocessor-based circuitry; user-intuitive design; and waterproof housing. A true one-handed instrument, the PT4 is easy to calibrate and easy to […]
The Myron L ULTRAPEN™ PT4 Free Chlorine Pen is designed to be extremely accurate, fast, and simple to use in diverse water quality applications. Advanced features include automatic temperature compensation in calibration mode; highly stable microprocessor-based circuitry; user-intuitive design; and waterproof housing. A true one-handed instrument, the PT4 is easy to calibrate and easy to use. To take a measurement, you simply push a button then dip the PT4 in solution. Results display in seconds.
1. Push Button — turns PT4 on; selects mode and unit preferences.
2. Battery Cap — provides access to battery for replacement.
3. pocket Clip — holds PT4 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
6. LED Indicator Light — indicates when to dip PT4 in solution, when measurement is in progress, and when to remove PT4 from solution.
7. FCE Sensor — measures Free Chlorine Equivalent of a solution.
8. Soaker Cap — contains Sensor Storage Solution to maintain sensor hydration. To remove, twist the soaker cap while pulling off using caution not to spill the Storage Solution. To replace, fill the soaker cap half full with Storage Solution. Twist the soaker cap while pushing back on, using caution, as excess Storage Solution may squirt out.
CAUTION: Do NOT push the soaker cap beyond the Cap Stop as sensor damage WILL
NOTE: The formation of KCl crystals around the soaker cap is normal. These crystals do not affect the sensor life, performance, or accuracy provided they are rinsed off with water prior to a test.
9. Scoop — used to hold sample solution when dipping is not possible. To install, push the scoop onto the sensor while shifting side-to-s
scoop off while shifting side-to-side. Verify the fully inserted into the PT4. If not, reinstall per FCE Sensor Replacement section on page 5. To use, hold the scoop directly under a vertical stream during measurement, avoiding bubbles.
10. Holster — run your belt through the strap in the back of the 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.
Free Chlorine: 0.00 – 10.00ppm
Free Chlorine Accuracy: < 5.00ppm ±0.3ppm, ≥ 5.00ppm ±0.5ppm
Free Chlorine Resolution: 0.01 ppm
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
Operating/Storage Temperature: 0 – 55ºC or 32 – 131ºF
Calibration Standard Solutions: pH4, pH7, pH10, ORP80, ORP260, ORP470
Enclosure Ratings: IP67 and NEMA6
EN61236-1: 2006 – Annex A: 2008: Electrostatic discharge to the PT4 may cause it to spontaneously turn on. If this occurs, the PT4 will turn off.
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.
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
TweetINTRODUCTION AND OVERVIEW The most popular germicide used in water treatment is chlorine, which kills bacteria by way of its power as an oxidizing agent. Chlorine is used not only as a primary disinfectant at the beginning of the treatment process, but also at the end to establish a residual level of disinfection during distribution […]
INTRODUCTION AND OVERVIEW
The most popular germicide used in water treatment is chlorine, which kills bacteria by way of its power as an oxidizing agent. Chlorine is used not only as a primary disinfectant at the beginning of the treatment process, but also at the end to establish a residual level of disinfection during distribution as a guard against future contamination.
The most popular field test instruments and test systems for judging the level of residual chlorine, also called Free Available Chlorine (FAC), are based on colorimetric methods whereby dyeing agents are added to the sample being tested. These additives react to FAC causing a color change in the test sample. While they may detect the presence of FAC, they do not directly measure the electrochemical characteristic of FAC responsible for its disinfecting power: Oxidation-Reduction Potential (ORP). They give an incomplete and sometimes misleading picture of sanitizing strength. These methods have gained industry-wide acceptance. Unfortunately, so have the weaknesses and inaccuracies inherent to them.
The Free Chlorine Equivalent (FCE) feature avoids these pitfalls by directly measuring ORP, the germ-killing property of chlorine and other oxidizing germicides. It displays both the ORP reading (in millivolts DC) for the sample being tested as well as an equivalent free chlorine concentration in familiar ppm (parts per million). It accounts for the very significant effect of changing pH on chlorine sanitizing power; can be used for other types of oxidizing germicides and; will track the effect of additives, such as cyanuric acid, that degrade chlorine effectivity without changing the actual concentration of free available chlorine present.
NaOCl, common household bleach (5.3% NaOCl by weight) is the most popular chlorinating agent in use today. When added to water it hydrolyzes as:
NaOCl + H2O HOCl + Na+ + OH-
Sodium hypochlorite Water Hypochlorous acid Sodium ion Hydroxide
Additionally, some of the HOCl dissociates into H+ and OCl-:
HOCl H+ + OCl-
Hypochlorous acid hydrogen ion hypochlorite ion
Both HOCl and OCl- are oxidants and effective germicides, particularly against bacteria and viruses, with some effectivity against protozoa and endospores. HOCl is the stronger and more effective of the two species.
When chlorine is added to water, not all of it is available to act against future contaminates. Some is deactivated by sunlight. Some is consumed by reactions with other chemicals in the water or by out-gassing as Cl2. More commonly, it is used up directly by disinfection of the pathogens already
present in the water or by combining with ammonia (NH3) and ammonium (NH4+) (byproducts of living bacteria) to form various chloramine compounds.
Chlorine Demand is the amount of chlorine in solution that is used up or inactivated after a period of time and therefore not available as a germicide.
Free Available Chlorine
Free Available Chlorine (FAC) is any residual chlorine that is available, after the chlorine demand is met, to react with new sources of bacteria or other contaminants. According to White’s Handbook of Chlorination and Alternative Disinfectants, 5th edition, this is the sum of the all of the chemical species that contain a chlorine atom in the 0 or +1 oxidation state and are not combined with ammonia or other organic nitrogen. Some species of FAC that might be present are:
• Molecular chlorine: Cl2
• Hypochlorous acid: HOCl
• Hypochlorite: OCl-
• Trichoride: Cl3- a complex formed by molecular chlorine and the chloride ions (Cl-)
In most applications the two most common species of free chlorine will be HOCl and OCl-. Much of the Cl2 will hydrolyze into HOCl that, depending on pH, will stay in the form of HOCl or partially dissociate into OCl-. Cl3- is very unstable and only trace amounts will be present. In fact, in most of the literature describing chlorination and the monitoring of chlorine residuals, free chlorine is considered to be the sum of HOCl and OCl-.
Chlorine dioxide, ClO2, is another chlorine derivative used in some public water supplies as a disinfectant. It is 10 times more soluble in water than chlorine and doesn’t hydrolyze into HOCl or dissociate into OCl-. In the absence of oxidizable substances and in the presence of hydroxyl ions, ClO2 will dissolve in water then decompose slowly forming chlorite ions (ClO2-) and chlorate ions (ClO3-), both of which are oxidants fitting White’s definition of free chlorine.
All other things being stable (temperature, pH, etc.), ORP values are related to FAC concentration levels. As the concentration of FAC in solution rises or falls, regardless of the species (HOCl, OCl-, ClO2-, ClO3- or Cl3-), the ORP value does, as well.
Combined and Total Chlorine
The term Combined Chlorine usually refers to residual chlorine that has combined with NH3 or NH4+ to form monochloramine (NH2Cl),
dichloramine (NHCl2) or trichloramine (NCl3). Combined chlorine is noteworthy here because chloramines are oxidizers and are used as germicides, though their reduction potential and therefore, disinfecting power is lower than other species of chlorine, such as HOCl, OCl- or ClO2.
Total chlorine is the sum of FAC and Combined Chlorine. An advantage of ORP-based systems is
that the aggregate ORP value of the water being tested includes the ORP levels contributed by all oxidizers, including chloramines. Therefore, ORP- based measurements automatically take into account Total Chlorine and can readily be used to judge total sanitizing strength.
Chlorine as an Oxidizing Germicide
Both HOCl and OCl- are oxidants and as such their effectivity as germicides can be determined using
ORP measurements. The cytoplasm and proteins in the cell walls of many harmful microbes are negatively charged (they have extra electrons). Any oxidant that comes into contact with the organism will gain electrons at the expense of the proteins, denaturing those proteins and killing the organism.
When enough chlorine is added to water to reach an ORP value of 650mV to 700mV, bacteria such as E. coli and Salmonella can be killed after only 30 seconds of exposure. Many yeast species and fungi can be killed with exposure of only a few minutes. Even ORP values of 350mV to 500mV indicate effective levels of chlorination with satisfactory microbe kill levels, although exposure times are required to be in the minutes rather than seconds.
The Importance of pH
pH significantly changes relative effectiveness of chlorine as a disinfectant. Different species of chlorine ions are more prevalent at different pH levels. Under typical water treatment conditions in the pH range 6–9, HOCl and OCl- are the main chlorine species. Depending on pH level, the ratio of these two free chlorine species changes.
Figure 1 – Distribution of Free Chlorine Species in Aqueous Solutions
Figure 1 shows that chlorine hydrolysis into HOCl is almost complete at pH ≤ 4. Dissociation of HOCl into OCl- begins around 5.5 pH and increases dramatically thereafter2. This is important because HOCl and OCl- do not have the same effectivity as disinfectants. HOCl can be 80-100% more effective as a disinfectant than OCl-. Optimum disinfection occurs at pH 5 to 6.5 where HOCl is the prevailing species of free chlorine present. As pH rises above that level, the ratio shifts towards being primarily OCl-. At pH 7.5 the ratio is about even. When the pH value rises to 8 or higher, OCl- is the dominant species. Therefore, assuming the concentration of Cl2 species is constant, the higher the pH of the solution rises above 5.5, the lower the oxidation capability and disinfecting power of the FAC.
The bottom line is knowing the concentration of FAC ions in a solution without taking pH into account can give an incomplete and sometimes incorrect picture of disinfecting power.
WHY A CHANGE IS NEEDED
The Problem with Colorimetric Testing
First and foremost, colorimetric tests only report how much chlorine is present, and as we saw in the previous section, knowing “how much” is not at all the same as knowing “how effective”.
Colorimeters and DPD kits add a reagent or several reagents to the water being tested that causes a color change representing the amount of FAC in water. In fact, they fundamentally change the chemistry of the water just to get an easy measurement.
The most obvious change is related to pH. The typical reagent/dye used in the process forces the pH of the sample to a specific level, usually 6.5 pH and thus radically alters the HOCl to OCl- ratio. If the original sample was at a pH of 7.4 to 7.6 (suggested levels for pools and spas) about 50% of the FAC present would be in the form of HOCl. At a pH of 6.5 this ratio rises to nearly 90%. While the actual concentration of FAC may be correct, a fact entirely overlooked is that the FAC in the source water includes about 40% of the much weaker sanitizing OCl-.
If that were the only change being made to the chemistry of the sample, it would be severe enough.
Figure 2 shows the result of a comparison test made using a UV spectrophotometer on two samples of water. Both were taken from a master water sample containing 5 ppm Cl2 prepared using a closed system that ensured no other oxidants or interferants were present. One was processed using a colorimeter reagent according to its operator’s manual instructions. The other was left untreated.
Figure 2: Chemical Alteration of Chlorinated Water by Colorimeter Additives
UV spectrophotometric analysis shows how dramatically the chemistry of the sample was changed by the addition of the colorimeter’s coloring reagent.
• The shift in the center of the spike indicates that the species of chlorine present has been altered. What was OCl- is now some other chemical species.
• The amplitude of the spike demonstrates how severely the amount of chlorine has been amplified.
• The absorption spectra where OCl- used to be is significantly depressed.
Because the area of UV absorption spectra where any OCl- would appear is so depressed, it is clear that a radical alteration is taking place above and
beyond simply changing the pH. The “ppm” value reported for the chlorine content of the water seems to be converted to a single species whose
concentration is significantly higher than the original OCl- content.
Even assuming a linear relationship between this altered chemistry and the original FAC content of the water that might be factored into the final colorimetric measurement, by completely divorcing the measurement from the pH of the source water, any direct correlation to the reduction potential of the FAC present and, therefore, real disinfecting power, is lost.
ORP = DISINFECTING POWER
What is ORP?
ORP is the acronym for Oxidation Reduction (REDOX) Potential. It is a differential measurement of the mV potentials built up between two electrodes exposed to solutions containing oxidants and/or reductants. ORP describes the net magnitude and direction of the flow of electrons between pairs of chemical species, called REDOX pairs. In REDOX reactions, one chemical of the pair loses electrons while the other chemical gains electrons. The chemicals that acquire electrons are called the oxidants (HOCl, OCl-, ClO2, bromine, hydrogen peroxide, etc.). The chemicals that give up electrons are called the reductants (Li, Mg2+, Fe2+, Cr, 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 an isolated reservoir of highly concentrated salt solution. When the solution being measured has a high concentration of oxidizers, it accepts more electrons than it looses and the measurement electrode develops a higher electrical potential than the stable potential of the reference electrode. A voltmeter in line with the two electrodes will display this difference in electrical potential (reported in mV). Once the entire system reaches equilibrium, the resulting net potential difference represents the Oxidation Reduction Potential (ORP). A positive reading indicates an oxidizing solution, and a negative reading indicates a reducing solution. More positive or negative values mean the oxidants or reductants present are stronger, they are present in higher concentrations or both.
What Does ORP Measure?
Measuring ORP is the most direct way to determine the efficacy of oxidizing disinfectants in aqueous solutions. It measures the actual chemical mechanism by which oxidizers, like chlorine, kill bacteria and viruses. The higher the ORP value, the stronger the aggregate residual oxidizing power of the solution, the more aggressively the oxidants in it will take electrons from the cells of microbes and, therefore, the more efficiently and effectively any source of new microbial contamination will be neutralized.
Also, because ORP measures the total reduction potential of a solution, ORP measures the total efficacy of all oxidizing sanitizers in solution: hypochlorous acid, hypochlorite, monochloramine, dichloramine, hypobromous acid, ozone, peracetic acid, bromochlorodimethylhydantoin, etc.
Can ORP Replace Free Chlorine Measurements?
When correlated with known disinfection control methods, measurements and bacterial plate counts, this type of measurement gives an accurate picture of the residual chlorine sanitizing activity reported as an empirical number that is not subject to visual interpretations. Solutions with certain ORP levels kill microbes at a certain rate. Period!
ORP was first studied at Harvard University in the 1930s as a method for measuring and monitoring microbial disinfection. It has been advocated as the best way to judge residual disinfecting power of chlorinated water by water quality experts since the 1960s. ORP has long been used in bathing waters as the only means for automatic chemical dosing. The World Health Organization (WHO) suggests an initial ORP value of between 680-720 mV for safe bathing water3 and ~800 mV for safe drinking water.
For the purpose of pretreatment screening to detect chlorine levels prior to contact with chlorine- sensitive RO membranes, some manufacturers of RO membranes and other water quality treatment equipment will also specify an ORP tolerance value for prescreening and influent control.
There are, however, applications where reporting residual disinfecting power in terms of FAC concentrations is preferred and sometimes required. While ORP measurements do not directly measure the concentration of FAC, they can be correlated to free chlorine levels in ppm. Variables such as pH and temperature must be accounted for or controlled. Interfering chemicals that might be present, such as other oxidants or reductants, must also be accounted for, or better yet, removed.
Once all these factors are known or controlled, ORP values can be linked to concentrations either by way of laboratory experimentation or via mathematical formulas like the Nernst Equation, an equation that describes the relationship between the electrode potential of a specific chemical in a solution and its concentration. In either case this is an often complex and laborious process … until now.
FCE = HANDHELD ORP ACCURACY
ORP Relevance in a Handheld Instrument
The Myron L Company has developed an innovative method for using ORP-based measurement to directly monitor the disinfecting power of free chlorine and report the result in both familiar ppm units as well as straight ORP mV values.
Myron L Company’s FCE function utilizes the accurate and reliable electronic design of Myron L Company’s instruments combined with simple one- button operation to make ORP-based chlorine measurement available in an easy-to-use, handheld field instrument. Other handheld instruments may measure ORP, but only a Myron L Company instrument equipped with FCE quickly correlates ORP and pH with FAC concentration. The FCE function also includes a predictive algorithm that extrapolates a final, stable ORP value of a solution without waiting out the long response time of the typical ORP sensor.
When the FCE function is active, the instrument display alternates between the Predicative ORP reading (mV) and the Free Chlorine Equivalent (FCE) concentration (ppm). Together these features combine to make ORP-based free chlorine measurement relevant in a handheld field instrument.
FCE – How and Why it Works
The Myron L Company FCE feature cross-references ORP values with pH levels to automatically arrive at a concentration value for FAC that reflects the effect of pH on the ratio of HOCl to OCl-. This correlation is derived from a series of experiments in which exact amounts of chlorine (in the form of laboratory grade bleach: 5% NaOCl; 95% H2O) were added to deionized water in a closed system, thus controlling and excluding possible interferants. By using both a pH measurement and an ORP measurement, FCE can determine the relative contributions of HOCl and OCl- to the final ORP value and factors them into a final concentration calculation.
Figure 3 – Sample Experimental Data Relating FAC ppm to ORP and pH
Similar experiments were performed using water to which precise amounts of calcium chloride (CaCl2) and sodium bicarbonate (NaHCO3) were added to slightly buffer the water. This allows the FC feature to correlate low ORP values to the typically low FAC concentrations of tap water after it has been in the municipal water system for several days.
FCE – pH Included, Not Ignored
Unlike other FAC test methods that ignore the effect of pH on sanitizing power by artificially forcing the pH of their test sample to a single value, Myron L Company’s FCE includes pH in its concentration calculation. This capability gives Myron L Company’s FCE the ability to compensate for the effect of the changing ratio of chlorine species as pH
changes, resulting in a FAC concentration value germane to the actual sanitizing power of the source water. OCl- is measured as OCl-, and HOCl is measured as HOCl. Those users who are primarily concerned with or who prefer free chlorine concentration levels have a reliable measurement that gives consistent and comparable results, reading to reading, without having to rigorously control or artificially manipulate the sample’s pH.
In addition, because the FCE function displays both the FAC concentration and a predicted, stable ORP value, the user can, by comparing these two values from successive measurements, track how ORP (and disinfecting power) falls as pH rises and how ORP rises as pH is lowered when concentration is constant.
FCE – Chemistry Measured, Not Altered
Both DPD kits and colorimeters may tell the user the FAC concentration of the sample in the test tube, but since the chemistry of that sample is quite different from the source water being analyzed, the results are imprecisely related to actual disinfection power.
DPD kits and colorimeters only imply true disinfecting power; they do not measure it, and that is, after all, the whole point of the exercise.
The Myron L Company FCE method avoids these pitfalls and inaccuracies. FCE measures the real, unaltered chemistry of source water, including moment-to-moment changes in that chemistry.
The following controlled study shows exactly how differently the two methods respond, particularly at the high end where the effects of changes in pH are the greatest. In this study measurements were made with a digital colorimeter and a Myron L Company Ultrameter II 6P equipped with FCE. The solutions tested were made with various known concentrations of NaOCl in deionized water. The water was heated to above 80°C to remove any CO2 and, therefore, avoid interference from REDOX reactions between HOCL, OCl- and carbonates (HCO3).
Table 1 – Comparison of FCE to Digital Colorimeter
In this study as the pH rises and the ratio of OCl- to HOCL rises dramatically, the FCE is able to accurately track the changing concentration of FAC. The colorimeter’s results do not.
FCE – Handheld ORP Accuracy Without the ORP Delay
One of the challenges in implementing an ORP- based free chlorine measurement in a handheld field instrument is the sometimes lengthy response time of ORP sensors. It is not uncommon for an ORP sensor to take 12 to 15 minutes to arrive at a valid stable reading. In extreme cases, such as an older sensor in poor condition and measuring a complex solution with a very low ionic strength, the ORP measurement can take up to an hour to fully stabilize. Obviously, for a handheld instrument these are unacceptably long times.
The Myron L Company FCE function includes a pioneering feature that dramatically reduces the wait for stable ORP readings. This unique feature determines an extrapolated, final, stabilized ORP reading within 1 to 2 minutes rather than the typical 15 minutes or hours for other ORP systems.
The Predictive ORP feature’s calculations are based on a model of sensor behavior developed through a series of experiments that measured the response time of a representative sample of ORP sensors over a range of controlled chlorine concentrations. The results of this set of experiments revealed that the shape of the curve is very similar for various ORP levels differing only in the initial starting point and the final stabilized reading.
Figure 4 – Example of ORP Sensor Response Study
Using a proprietary curve-matching algorithm, the Predictive ORP feature determines what point along the typical sensor response curve a measurement occurred and extrapolates an appropriate final reading. This extrapolated value is used to calculate the FCE ppm value without having to wait for the sensor to stabilize and is also reported directly to the instrument’s display.
FCE – FLEXIBILITY FOR THE REAL WORLD
Another advantage of an ORP-based measurement such as the Myron L Company FCE feature is that, within the limits of its range, it can be used to measure the disinfection effectivity of ANY oxidizing germicide. Myron L Company FCE measurement can be used with non-bleach oxidants, such as chloramines or even non-chlorine oxidants, such as peracetic acid, bromine or iodine.
The Predictive ORP value displayed when the FCE function is active is directly relevant for monitoring and controlling the sanitizing effectivity of oxidizing sanitizers besides HOCl and OCl-.
While the concentration values reported by the FCE function will not be absolutely correct for non-FAC oxidants, since they are based on a HOCl / OCl- model, FCE can still be an effective tool for monitoring relative changes in concentration levels. For absolute accuracy a correlative study should be performed to relate concentration levels of the oxidant in question to the ORP values displayed by the Predictive ORP feature and ppm values output by the FCE.
FCE = Effective Chloramine Control
A perfect example of the Myron L Company FCE ‘s flexibility is the use of chloramines as a germicide.
Chloramines are formed when chlorine (Cl2) and ammonia (NH3) come into contact, forming three different inorganic chemicals: monochloramine (NH2Cl), dichloramine (NHCl2) and trichloramine (NCl3). In some applications chloramines are considered an unavoidable side effect of the chlorination process; however, because they are also oxidants, there are other applications where they are used as the primary disinfectant in water treatment.
Chloramines are effective at killing bacteria and other microorganisms, but because their relative ORP levels are lower compared to HOCl or OCl- at the same concentrations, the disinfection process is slower.
Table 2 – Electrode Potentials of Chloramines vs. HOCl
On the plus side, chloramines last longer than HOCl and OCl- (as long as 23 days in some cases), impart a less strong flavor or smell and their sanitizing
strength is not appreciably affected by changing pH.
Most importantly, chloramine-based water treatment methods produce much fewer hazardous byproducts. The US EPA limits the total concentration of the four chief hazardous byproducts of chlorination (chloroform, bromoform, bromodichloromethane, and dibromochloromethane), referred to as total trihalomethanes (TTHM), to 80 parts per billion in treated water. To avoid exceeding theses standards, many municipal water districts prefer using chloramine rather than chlorine.
The following table shows typical ORP values for various concentrations of monochloramine (NH2Cl).
Table 3 – ORP Values for NH2Cl in Pure Water
When ORP levels of NH2Cl approach and exceed 500 mV, effective sanitization occurs with exposure times of 20 to 30 minutes. This is more than adequate for municipal water treatment.
Since Myron L Company FCE function bases its measurement on ORP, it presents an empirical, easy to interpret measurement, both in terms of the Predictive ORP display and the FAC equivalent concentration, allowing the user to monitor falling chloramine concentration as disinfection proceeds.
FCE and Cyanuric Acid (CYA) – Don’t Guess. Know!
Outdoor pool maintenance is a prime application where ORP-based chlorine measurement should be preferred. The use of chlorine to sanitize pools runs afoul of the fact that much of the chlorine added to an outdoor pool is deactivated by exposure to UV radiation in sunlight.
Cyanuric Acid (CYA) is often added to the pool water to “protect” FAC. In a typical pool at 7.6 pH about 50% of the FAC is OCl-, which reacts to UV radiation that passes through the Earth’s ozone layer (290nm). CYA combines with FAC to form N-chlorinated-cyanurates, which only react to UV radiation (215nm to 235nm) removed by the Earth’s ozone layer. Since N-chlorinated-cyanurates are also oxidizers, they also act as germicides. Unfortunately, they have much lower reduction potentials and, therefore, a much lower strength as a germicide.
Figure 5 – Effect of Cyanuric Acid on Chlorine ORP Values
Pool maintenance websites that advocate the use of cyanuric acid (not all of them do) often recommend levels of 40 to 80 ppm. Figure 5 shows how severely ORP and disinfecting power are affected by CYA.
The addition of only 20 ppm CYA decreases the pool water’s ORP 120 mV, reducing the effectivity of FAC from 1.5 ppm to an effectivity that is equivalent to only 0.3 ppm. Adding 40 ppm, or worse, 80 ppm, reduces sanitizing strength even more severely. This is definitely a case where more is not better.
A 1972 study on water chlorination showed that water treated with enough chlorine to kill 100% of the E. coli present in 3 minutes or less required almost 6 times as much chlorine be added for the same effect when 50 ppm of CYA was added.
Cyanuric acid beneficially affects pool chlorination by greatly reducing that portion of chlorine demand related to loss due to UV. Unfortunately, if you are using a colorimeter or DPD kit, it will tell you that your FAC concentration is unchanged and significantly misrepresent sanitizing strength
The Myron L Company FCE function’s ability to react to changes in ORP makes it an ideal tool for keeping track of how CYA affects residual sanitizing power when added to a chlorinated pool. The Predicative ORP display provides a direct and effective way to monitor changes in ORP values as CYA concentration increases. Because the FCE ppm
display reacts to changes in ORP and pH, it will reflect changes in the sanitizing strength as an “equivalent” or “effective” FAC concentration.
Judging the true effectivity of chlorine as an oxidizing germicide requires more than just knowing how much chlorine is present. Changing pH or the addition of additives like cyanuric acid can radically alter the effectivity of the chlorine present. To accurately measure the effects of these issues requires a test method based on the precise measurement of ORP (the chemical characteristic directly responsible for killing microbes like bacteria and viruses) and cross-referenced to pH.
The Myron L Company FCE is the first measurement function that allows handheld, field instruments to integrate ORP and pH measurements into a system for monitoring the residual disinfecting power of free available chlorine in aqueous solutions.
• It provides an empirical measurement that does not require interpretation.
• It is not affected by water color or turbidity.
• It measures the true chemistry of the water, unaltered.
• It accounts for changes in pH.
• It reports the effects of CYA on disinfecting power.
• It can be used to monitor non-chlorine oxidants.
Myron L Meters features the Myron L FCE function in several instruments that read free chlorine – the Ultrameter II 6P, the Ultrameter III 9P, the PoolPro PS9 and PS6 models, and the
new Ultrapen PT4, soon to be released.