pH and ORP Sensors

pH electrodes and sensors are the sensing portions of a pH measurement. Various installation options including retractable, flow thru, immersion, and direct insertion. Proper pH electrode/sensor selection is critical for optimal measurement results.

The FU20 and FU24, all-in-one pH and ORP, sensors show how Yokogawa applies the motto "Simple is best" to sensor technology.

The SC25V is a pH sensor in a 12 mm design that includes an integral temperature element and a Liquid earth electrode.

The cation differential pH and ORP sensors were designed for difficult applications where conventional sensors are ineffective. These include measurements such as brine solutions to applications as diverse as electrolysis processes and cheese manufacturing.

The heart of a pH measuring loop is the electrode system. Yokogawa has designed a wide range of electrodes to ensure this heart keeps beating under the most severe conditions.

Achieving accurate and reliable readings using a traditional pH analyzer is challenging, however with the right equipment stable and accurate pure water pH measurements can be accomplished. Yokogawa's specialized bellomatic pH sensor is proven best solution for high purity water applications. For those individuals that do not like the maintenance of refilling sensors, then the FU24 which incorporates the successful patented bellow system in an All-in-one body is the ideal solution.

The PH71/PH72 pH and/or ORP meter is a Compact, Easy-to-use, Drip proof – Ideal for Field Use. Features "One-Touch Calibration" and Temperature Compensation. Laboratory-Grade Intelligent pH Meters – Sized and Priced to Fit in Your Pocket

These sensors feature the latest innovations in pH glass formulation, reference systems, and reference electrolytes. They offer supperior accuracy and stability, even after repeated sterilizations.

The PH87 retractable assembly is suitable for "Hot-Tap" service, allowing for removal from a pressurized process line or vessel without interrupting the flow or draining the tank.  The housing assemblies are constructed of chemically resistant titanium sheathes and are used with Model PH97 rugged sensors.  

The pneumatic retractable holder EXAtrac RF20 (Extrac 810 and 820) is made for installation of 12mm sensors on tanks or pipelines where the sensor has to be removed without interruptions or shutdowns and in the hash applications where frequent cleaning is of vital importance for a good pH measurement.

A pH electrode is as good as its maintenance; this is especially true in harsh environments. For industrial applications and particularly for automatic process measurements it is of the greatest importance that the sensitive part of a glass electrode and the diaphragm of a reference electrode are kept clean.

Buffer solutions are needed as an indispensable tool for maintaining an accurate pH measurement. Buffer solutions are used as references points for calibration and adjustment of pH measurements to compensate for aging and deterioration.

  • More than 1,000 field devices designed to the PROFIBUS specifications installed in the state-of-the-art water reclamation plant.
  • The high reliability and accuracy of our field devices contributes to the minimization of maintenance costs over the entire plant lifecycle.
Application Note

For control of batch neutralization, a pH measurement coupled with a timer-controlled chemical feed scheme provides very satisfactory results.

This system can be adapted for either acid waste or alkaline waste neutralization.

Application Note

The term "cooling tower" is used to describe both direct (open circuit) and indirect (closed circuit) heat rejection equipment. Cooling towers are heat-transfer units, used to remove heat from any water-cooled system. The cooled water is then re-circulated (and thus, recycled) back into the system. Since the process water is re-circulated, the mineral concentration increases as a result of the evaporation. (AN10B01B20-01E)

Industry:Refining, Food and Beverage, Power, Oil and Gas, Pulp and Paper, Chemical


There are a number of suppliers of oil and fat products used for edible purposes. These products include, but are not limited to olive oil, peanut oil, soybean oil, sunflower oil, lard, shortening, butter, and margarine. The raw materials for these products include animal by-products, fleshy fruits (palm and olive), and oilseeds. 

Industry:Food and Beverage


Measurement of pH in high purity water presents many difficulties. Yokogawa's pH instrument's design success comes from addressing the unique challenges of the application.


Process liquid analyzers such as pH meters, conductivity meters, ORP meters, and density meters play an important role at electrolysis plants in the control of concentrations of various process solutions. This requires both precision and stability under harsh conditions that include highly corrosive substances, high temperatures, and many impurities.


Most zinc are produced at hydrometallurgically, where a high-grade zinc product can be obtained and valuable metals mixed in the raw material can be recovered. In the hydrometallurgy, the raw material of zinc concentrate is roasted and then dissolved in sulfuric acid to remove impurities. The process called leaching and pH control of the leachate is important.

Industry:Chemical, Power


The control of the world's water resource is arguably one of the most important issues. Water demand from industry and domestic users is set to rise throughout the industrialized world. Yokogawa has been applying minimized maintenance measurement systems.


Cyanide-bearing wastewater from mining and electroplating facilities and certain types of chemical plants is toxic and must be treated by oxidation with chlorine or chloride to bring the cyanide concentration within regulatory limits.

Industry:Electrical and Electronics


In flue gas desulfurization systems that use magnesium hydroxide (Mg(OH)2) slurry, the consumption of the desulfurization agent (Mg(OH)2) is controlled by using online pH analyzers. A great concern in the pH measurement is heavy staining of the pH electrodes by the Mg(OH)2 slurry. To ensure accurate measurement, frequent cleaning of the electrodes with an acid is required, adding to both maintenance workload and cost.

Industry:Chemical, Power


The treatment of wastewater from pulp and paper plants is a serious environmental concern. Yokogawa's submersion holder with an ultrasonic+air-jet cleaner (customized product) can reduce the manual cleaning frequency to just once every one or two months.

Industry:Pulp & Paper


Continuous technology improvement is ongoing in the pulp & paper industry to obtain the best possible performance. Problems at the wet end (stock preparation) can rarely be corrected downstream. That is why monitoring and controlling pH in pulp stock is critical to the paper making process. Essentially, at every stage in the manufacture of paper, correct pH values play a vital role.


Reverse osmosis (RO) is a separation process that uses pressure to force a solution through a membrane that retains the solute on one side and allows the pure solvent to pass to the other side. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure.


Continuous technology improvement is ongoing in the pulp & paper industry to obtain the best possible performance. The improved plant performance translates to the higher quality improvement and lower cost, and simultaneously environmental friendly plant operation.


Wastewater from electroplating facilities and certain types of chemical plants contains toxic forms of hexavalent chromium such as chromate and dichromate. The hexavalent chromium in this wastewater must be reduced before the water can be discharged. This requires a two-step process: hexavalent chromium (CR6) is reduced to trivalent chromium (CR3); and CR3 is precipitated as chromium hydroxide.

Industry:Electrical and Electronics


Sour Water is the wastewater that is produced from atmospheric and vacuum crude columns at refineries. Hydrogen sulfide and ammonia are typical components in sour water that need to be removed before the water can be reused elsewhere in the plant. Removal of these components is done by sending the sour water from the process to a stripping tower where heat, in the form of steam, is applied.


Power plant boiler houses designed to burn coal or high sulfur oil are required by Federal and State pollution regulations to "scrub" (remove) sulfur dioxide from flue gasses to meet emission limits. SO2 in flue gasses is known to be harmful to the environment, as it is one contributor to the formation of acid rain. pH control is critical for the proper functioning of the scrubber system.

Application Note

Wastes have been considered to be a serious worldwide environmental problem in recent years. Because of increasing pollution, these wastes should be treated. However, industrial wastes can contain a number of valuable organic components. Recovery of these components is important economically. Using conventional distillation techniques, the separation of acetic acid and water is both impractical and uneconomical, because it often requires large number of trays and a high reflux ratio. In practice special techniques are used depending on the concentration of acetic acid. 


Many Ethanol plants running today are using a combination style pH electrode with a non-flowing reference to measure pH in the Mash Slurry transfer line from the Mash slurry mix tank to cook. The Mash is being pumped out of the Mash Slurry tank is at approximately 180 °F and 40 to 60 psig.


The lifetime of a pH sensor has a significant impact on the overall annual costs of a pH measuring loop. Optimizing four key factors will decrease these costs and optimize process control and overall plant efficiency.

White Paper

ORP (Oxidation-Reduction Potential) is the measurement, in millivolts, of a solution's capacity for electron transfer (oxidation or reduction). ORP measurement may also be called REDOX for REDuction OXidation. The name reflects that fact that within a chemical reaction reduction and oxidation are complementary; one cannot occur without the other.

Media Publication
No, the PH21 does not have a Liquid Earth (LE) electrode. The LE is not needed in many of the applications we target for this sensor. When necessary a seperate Liquid Earth connection can be connected to the SA11 using the screw termin...
The PR20, PR4A, and ISC40PR were discontinued in April of 2010. The PR10 is the replacement for these products. It is larger than the PR20 so installation changes are necessary in most cases. The PR20 had a 1" NPT process connection, and th...
Yes, it can be used as an analogue sensor connecting to the analog inputs of the pH transmitter.
Yokogawa offers the PH18 sensor. This sensor is nonglass and suitable for regular CIP and SIP cycles.
That is possible but not guaranteed. The 225 mm sensor body is longer, so it has more electrolyte. Often the reference electrode fails because the electrolyte is depleted as it diffuses through the reference junction into the process. With ...
Most pH sensors with a glass membrane cannot be mounted upside down. To absorb the thermal expansion of the internal buffer solution there is always a sizeable air bubble inside the sensor. When the sensor is mounted upside down the reference element...
Air bubbles are normal in pH sensors and in some reference sensors. They are necessary because the pH sensor is a sealed device with no vent. Without the air bubbles the expansion and contraction of the liquid with temperature changes could cause the...
The reference potential difference between 1 molar and 3.3 molar is approximately 30 mV. The sensitivity of a pH sensor at reference temperature is 59mV/pH. So if you combine a measuring cell filled with 3.3mol KCl with a reference cell with 1mol KCl...
PH Sensor Cleaning
Cleaning pH Sensors Basic Steps  Rinse electrode in clean water Clean by immersing the electrodes in a cleaning solution (see below).  Rinse Again Check with buffers Cleaning Solutions: If you know a specific way to clean the sens...
The short answer to this question is NO. But, there is a long answer that will give you another option. Yokogawa has created a Submersible Sensor Kit (part number M1289XT) for the FU20 pH sensors - M1289XU for the FU24 sensor). It is also known as ...
Yes you can, but we do not recommend this method. A pH sensor has a reference electrode that has a low impedance to the process. If the process suffers from common mode voltages or ground loops it will be difficult to measure the ...
The FF20 flow through holder for PH can be ordered using the "pH Selection Guide Matrix" so that an entire system can be ordered with one line item. This does not work if you want a FF20 with an FU20 sensor. The Matrix does not contain the ...
Sensor lifetime is difficult to predict as it is dependent on a number of different factors such as pH value, temperature, pressure, composition of the process liquid, maintenance activity taken, storage conditions, and sensor handling. To ...
Yes and No.  Yes - after cleaning you need to verify that the analyzer is reading correctly. The easiest way is to see how it reads when placed in 2 pH buffer soltuions. This is what you do when calibrating.  No - If the readings are with...
This is a well-known pH problem that we call Diffusion Potential. If the sensor junction is partially plugged the electrical contact between electrolyte and process is not good. This results in a high diffusion potential and an error i...
Most of our pH sensors have a noble metal solution ground and our transmitters measures two values: 1.  the voltage between this solution ground, or liquid earth sensor and the pH sensor, and 2. the voltage between this solut...
Yes, the input module can be changed in the Converter.    See the FAQ: Which Input Module do I order for my FLXA21/202 analyzer? ...
NO!  Sensors that are not used need to be stored in a solution that guarantees that the sensor is ready for use. When the sensor is stored in pure water the salt will be washed out of the junction of the reference cell. This causes the sensor t...
First - when you receive a new Bellomatic sensor it is shipped with a rubber stopper inserted into the pressure port on the bottom of the sensor. You must remove this stopper before putting the sensor in service. DO NOT DISCARD THIS STOPPER! Put it i...
Yes, the SENCOM Module in these sensors allows a Modbus Master to connect using Modbus RTU protocol and access the following data: pH Temperature compensated pH ORP pH compensated ORP rH Temperature Junction resistance value Sensor details ...
It is very important that the cables maintain a very high impedance. If any moisture penetrates the cable the impedance will drop and the cable will short out the voltage generated by the pH sensors. This will cause errors or a total loss of mea...
A tiny crack in the membrane of a glass electrode is not always visible to the naked eye. Frequent shocks may create cracks in the glass that cause measurment errors. These cracks will cause the analyzer to read 0 mV and the ...
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    While we strive to provide the most safe and accurate information possible, we are not responsible for any loss or damages resulting from attempting to replicate the acts conducted in this video. Furthermore, we shall not be held liable for use or misuse of information contained in this video.


    This video covers a PR10 installation and extraction. While we strive to provide the most safe and accurate information possible, we are not responsible for any loss or damages resulting from attempting to replicate the acts conducted in this video. Furthermore, we shall not be held liable for use or misuse of information contained in this video.




    Are Pure water, Ultrapure water, UPW, or Water for Injection (WFI) important in your process? Would a better understanding of current water treatment equipment technology be useful? Would learning to better identify sources for potential process problem be helpful?

    Pure water, Ultrapure water, UPW, Water for Injection (WFI), high-purity water and deionized (DI) are all terms describing basically the same property. They refer to water which has been purified to the highest standards by removing all contaminants such as, organic and inorganic compounds; dissolved and particulate matter; volatile and non-volatile, reactive and inert; hydrophilic and hydrophobic; and dissolved gases. Pure water or conditioned water is used in a variety of processes across various industries; Power Generation, Pharma/Biotech, Semiconductor, and Drinking water are just a few examples. Please join us for a free 45 min webinar with 15 min Q&A section. As our presenter David H. Paul, Inc (DHP), gives an overview of high purity water treatment. What you will learn:

    • Understanding the purpose for each piece of equipment in a high purity treatment process flow
    • Basic overview of Reverse Osmosis Processes
    • Better understanding of when to "raise an alarm" when performance issues arise

    Information about the presenter: Since 1988, David H. Paul, Inc (DHP) has been the world's leader in reverse osmosis and high purity water treatment training. DHP has trained over 18,000 water treatment professionals worldwide. For information on additional High Purity Water Treatment and Reverse Osmosis Water Treatment training please click on the link to DHP's website:


    Watch this on-demand webinar to review and learn the theory behind pH measurement, the issues surrounding high purity pH measurements, and how to implement good calibration and maintenance procedures.


    Proper pretreatment is critical for minimizing problems and reducing the need for chemical cleaning. This webinar will teach you the most common pretreatment technologies and why it is important to monitor and maintain them. Join us to learn:

    • Why pretreatment is important
    • How pretreatment protects your RO units from scaling, fouling and chemical attacks
    • What to monitor and why

    Basic pH/ORP Theory and gain an understanding of:

    • How pH and ORP measurement works
    • The differences in measuring electrodes and reference electrodes
    • The difference between ORP and pH compensated ORP

    How to choose the right reference and measuring electrode for your application, which includes:

    • The differences and benefits between all-in-one vs. individual electrodes
    • The benefits of SMART sensors
    • The difference between traditional and differential pH maintenance
    • Best practices for cleaning and calibrating
    • The benefits of sensor diagnostics and how to interpret the information

    This video aims to answer the following: How does a traditional pH reference work and what are it's common problems? How does a sodium pH reference work and what are it's benefits? This webinar was presented February 12th, 2013.


    Each of the previous webinars covered the basics and the monitoring requirements for a high purity water treatment system that included a Reverse Osmosis (RO) treatment step. In this final webinar, we cover the problems that poor RO unit performance can produce in downstream process steps and in the end use water. The webinar series started with topics concerning raw water contaminants and will end with following contaminants through the RO membrane and into downstream treatment steps including Electrodeionization (EDI), mixed-bed ion exchange, 185 nm and 254 nm UV, ozone and more. Join us and learn:

    • What and why certain measurement parameters should be monitored
    • When to "raise the alarm" when issues arise

    A common use for RO is for purifying water, removing salts and other impurities to improve the color, taste and other properties. It is regularly used for commercial and residential water filtration and is also one of the methods used for desalinization of seawater. RO systems are capable of rejecting bacteria, salts, sugars, proteins, particles, dyes, and other constituents which have a molecular weight of greater than 150-250 Daltons. RO systems are designed for automatic operation and require routine preventative and corrective maintenance. Common problems include membrane fouling and the use of improper flow rates. The result is reduced throughput capacity and shortened runs. What you will learn:

    • Overview of Reverse Osmosis Processes
    • Understanding of RO technology
    • Understanding the importance of RO operation and maintenance

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