How to Choose the Right pH/ORP Sensor for Your Water Quality System

Features & Technology to Consider for Your Next pH Sensor

There are countless options and brands to choose from when trying to find the right pH/ORP Sensor for your application. Without guidance from an expert who understands how the sensor will be used, this task can easily become overwhelming and confusing. And, assuming you’ve at least found the right type of pH/ORP sensor, there are many features that could help make your process safer or more efficient.

Please visit our website for more information on this topic.

The first part of this post is dedicated to the technology and features that you should consider when choosing a pH Sensor, and then we will dive into the different types of sensors and what sorts of applications they best serve.

SMART-Enabled

• Allows the pH sensor to have a memory that holds calibration information so no calibration equipment needs to be brought out to the field. The sensors can be plugged right into the system to start measuring and be switched out with minimal downtime. This is advantageous for remote applications or multiple installations.

Junction Type for the Reference Cell

• Single junction electrodes are less expensive options that put the reference electrode cell in contact with the sample. If the application has conditions like high pressure, high temperature, high acidity, or high alkalinity, the reference electrode can become contaminated which leads to failure. This is known as sample ingress. Double junction electrodes have an inner and outer junction which isolates the reference electrode cell. This minimizes contamination even if sample ingress were to happen, making it conducive for samples that contain heavy metals. Triple junction electrodes further isolate the reference electrode cell, allowing for reliability and accuracy even with harsh samples.
• The material of the junction itself is also important. Some materials like Polytetrafluoroethylene (PTFE) are hydrophobic and provide chemical resistance, thereby preventing contamination or clogging that leads to unreliable readings. 

Housing & Glass Type

• The housing for the pH sensor should be strong, chemically resistant, and prevent leakage or humidity problems. Polyphenylene Sulfide (PPS) is an option that achieves these goals. Similarly, the glass of a pH sensor can be built to resist cracking, reduce sodium ion errors, and increase longevity. As always, it’s important to check the manufacturer’s specifications or talk with a knowledgeable engineer to be sure of what material is needed for your application.

Mounting Configurations & Accessories

There are many different types of pH sensor fittings and accessories that fit different types of applications. While this list is not exhaustive, it is a good reference for determining which mounting configuration is best for your pH/ORP sensor’s application.

• Insertion or Submersion - Using front-facing threads, insertion probes are used when measuring pH in flowing pipes. Using rear-facing threads, many of the probes can be submerged in a tank. 

• Retractable - usually installed in a ball valve that still allows sensor recalibration without shutting down your process. 

• Quik-Lok - Uses a compression style fitting which allows for quick installation and removal. It also enables variable insertion depths for installation.

• Low Flow Cell - takes a small continuous sample allowing you to control the flow across the sensor and maintain the highest precision possible.

• Refillable / Rebuildable - Allows you to refresh the electrolyte solution which gives the same probe a longer life. This is also helpful for special applications because special electrolytes can also be used. The electrolyte options for pH/ORP sensors are:

  • High Temperature - most suitable for use in highly acidic, basic, or oxidative solutions, and high-temperature applications.
  • Bio-Film Resistant - inhibits the growth of bacteria and algae.
  • Poisoning Resistant - most suitable for use in processes containing sulfides, mercaptans, and cyanides.
  • Oil Resistant - aimed for use in applications where light oils and greases can foul a sensor.
  • Scaling Resistant - targets applications where the precipitation of calcium magnesium salts like gypsum or water hardness coat over the electrode.
  • Metal Resistant - most suitable for use in applications where chloride in the reference electrolyte would react with the process.

Choosing a pH/ORP Sensor Based on Your Application

With an idea of what features or technology should be considered for your next pH sensor, a more informed decision can be made when shopping for a sensor based on the process or application. Manufacturers will design sensors with particular applications in mind. A more simple application may only need a single junction electrode, whereas a harsh environment with contaminants may need a double or triple junction electrode. Rosemount Analytical is one example of a manufacturer that does this. As we explore different applications, we will use different Rosemount Analytical pH Sensors for the sake of consistency.

General Purpose, Non-Coating pH Sensors

Sometimes a sensor designed for a special application isn’t necessary. General-purpose pH Sensors, like the Rosemount Analytical Model pH/ORP Sensor, are known for versatility and customizability. The Rosemount is SMART-enabled, has multiple options for glass type, and can be mounted in various configurations. With a double or triple junction reference cell, and a sealed PPS body, the is still a very durable option for most industries and applications. For processes that require higher performance or need to meet a specific need, keep reading below.

Non-Coating with Possible Poisoning pH Sensors

Some processes contain contaminates like sugar, ammonia, chloride, or sulfides, which can require a special kind of pH Sensor. Chemical or wastewater processing, pulp and paper, and mineral refining are a few examples of processes where these contaminants are present. One example of a pH sensor built for these sorts of processes is the Rosemount Analytical Model 385+ pH / ORP Sensor. It works with retractable mounting configurations, is SMART-enabled when used with an Analyzer or Transmitter, and utilizes triple-junction technology. The Rosemount Analytical Model 389 pH / ORP Sensor is a different model that works with insertion mounting configurations and is considered a combination sensor (pH, reference, and temperature).

Sanitary, Steam Sterilizable pH Sensors

Many industries need pH sensors for their ultra-clean steam-in-place (SIP) and clean-in-place (CIP) processes. The Rosemount Analytical Model Hx338+ pH Sensor is built with a unique Tri-Triple reference technology and can be used with insertion or retractable sensor mounting assemblies. Three separate peripheral liquid junctions make contact with the solution and two inner junctions protect the reference. The first junction eliminates flow sensitivity and maintains a steady reference signal. This technology fights poisoning ions even after numerous sterilization cycles, which makes it applicable for industries like biotechnology, pharmaceutical, and food processing.

Heavy-Duty Industry pH Sensors

Applications like mining or chemical/oil refining that use a viscous coating need a heavy-duty pH sensor that offers more durability. Rosemount Analytical designed their TUpH line of pH and ORP sensors for this reason. The Rosemount Analytical Model TUpH 396R / 396RVP pH/ORP Sensor is known for easy sensor removal, works with retractable mounting configurations, and has a titanium tube with EPDM seals.  For those who need a pH sensor designed for insertion or submersion mounting, there is the Rosemount Analytical Model TUpH 398 / 398VP pH/ORP Sensor which is also housed in a titanium tube. For easy installation or removal, the Rosemount Analytical Model TUpH 397 pH Sensor utilizes Quik-Lok technology for easy installation and removal for cleaning. The compression fitting of the Quik-Lok means that you don’t have to spin the actual probe for installation or removal and you can avoid twisting the wire.

Low-Conductivity pH Sensors

For applications that have low conductivity like in boiler feed water,  Rosemount designed the SQP-LQD Low Flow Panel (now replaced with part number --001) which enables the Model ph/ORP Sensor to work with inlet flow of 3-80gph and inlet pressures of 3-65psig. By controlling the flow across the sensing element, you control the fluctuations of the pH readings. This is especially important in low conductivity applications when there are few ions that come in contact with the pH glass and junction.

High-Temperature & High-Pressure pH Sensors

Processes requiring high performance (oil refining, chemical, pulp and paper, water and wastewater, metals and mining) often operate in high temperatures and pressures that can cause deterioration of the glass membrane, quicker depletion of the reference electrolyte, and increased stress on other sensor components. Rosemount designed their PERpH-X pH / ORP sensors to combat this additional stress on the sensors.

The Rosemount Analytical Model HT / HTVP ph/ORP Sensors work with Insertion or submersion (refillable) mounting configurations and are specially designed to handle these harsh conditions. Additionally, the enhanced double-junction reference is chemically resistant and has a larger surface area which allows for a more steady reference signal in dirty or oily applications.

For applications that require a retractable (refillable) mounting configuration, the Rosemount Analytical Model Model HT ph/ORP Sensor is another option that is housed in a titanium tube for added durability. Or, for applications that use insertion or submersion mounting, the Rosemount Analytical Model pH/ORP Sensor is a different pH / ORP sensor that utilizes many of the same PERpH-X features.

Special Use pH Sensors

Some applications like those that contain hydrofluoric acid (HF) require a different type of glass than other applications due to HF’s ability to attack the silicon-oxygen bonds that hold the glass matrix together. For insertion or submersion mounting configurations, the Rosemount Analytical Model TF396 pH Sensor has a glass-free design which also allows for less frequent calibration due to the sensor’s stability. Without a glass bulb, this allows for a wider range of applications that the sensor can be used for. Rosemount also has specially-formulated glass for the Model 372 pH Sensor which can reduce HF attack by more than a factor of ten.

Ready to Purchase a pH Sensor?

Overall, there is a lot of information to sort out to make sure the pH sensor life is maximized, the most precise measurements are being taken consistently, and the lifetime cost of ownership is minimized. If you have specific questions about what pH sensor is needed for your application, call or chat our applications engineers today.

Imagine being able to monitor your commercial pool equipment and chemical levels right from the palm of your hand, anywhere and anytime.

A pool automation system not only ensures proper water chemistry, but it also gives you remote and real-time control of your pool. It basically puts the pump room in the palm of your hand.

With the right system, you can monitor your water quality, review your tank levels, and be aware of leaks — without ever stepping foot inside your pump room.

But all pool systems aren’t created equal! If you want to find the right system to help you save money and provide the safest water possible, here are seven important questions to consider before making a decision.

What Combination of Hardware and Software Do I Need To Manage Chemical Dosing?

For many years, commercial facilities relied on hand dosing or chemical erosion feeders. However, as public safety has become more regulated, most building and health department codes now require some form of automation for the management of commercial pools and spas.

Traditional chemical control systems rely on a set of sensors to "sense" water chemistry levels and then include programming to "dispense" the right level of chemicals (i.e., liquid bleach, cal hypo, muriatic acid, etc.) to keep water appropriately balanced. While such systems offered an advancement over hand dosing, many operators have continued to struggle with the required calibration, the cleansing of probes, and other related tasks.

In recent years, the level of innovation around control systems has increased significantly. Newer systems, including our VivoPoint system, now provide online connectivity, modular sensor capabilities, 24/7 monitoring and more. In effect, the new systems are not just "controllers" but water managers that can reduce chemical costs, extend the life of equipment, and provide safer water.

Does the System Have an ORP Probe?

Traditional pool automation systems use an oxidation reduction potential (ORP) probe.

With competitive price and timely delivery, Yuhan sincerely hope to be your supplier and partner.

Additional resources:
Hardware for Your Software Radio - IEEE Spectrum
Safety and Efficacy of Chlorine Dioxide Gas
Grips; and how to use them! - CrossFit 306

ORP is the most common type of probe and has been used in the pool industry for many years. ORP is not a direct measurement of chlorine. The sensor doesn’t measure any specific chemicals, so it won’t differentiate between chlorine and bromine, for example.

ORP measures the water’s ability to oxidize any sanitizer present. If chlorine is free and available, it will oxidize and generate an ORP reading. If chlorine isn’t available, there won’t be a reading.

ORP readings are generated in millivolts, which can be difficult for the operator to understand. This can also cause issues for the health department, which will generate readings in true parts per million (PPM).

...Or Does It Have a Parts Per Million (PPM) Probe?

Chlorine testing using a PPM probe has become the standard in recent years. Although this type of technology is more expensive, it’s easier for owners and operators to use because it’s a direct test of the amount of chlorine in the water.

There are three primary methods to measure PPM: Calculated PPM, Selective Membrane PPM and Colorimetric PPM.

Calculated PPM — This is calculated based on the pool’s ORP and pH, and many pool automation controllers use this to provide a free chlorine measurement.

Selective Membrane PPM — Using a special membrane that only free chlorine ions can pass through, this system provides true readings of chlorine instead of indirect values derived from ORP and pH.

Colorimetric PPM — Colorimetric is a measurement system that uses chemical indicators for chlorine. The indicators react with the chlorine and produce a visible color change in the solution. The more chlorine present, the darker the color.

Choosing ORP vs. PPM

Both ORP and PPM probes have advantages and disadvantages, but the most important thing is to understand how the readings are generated in your pool automation system. Then you can determine your water’s chemistry and know what changes you need to make.

Some higher-end platforms show both ORP and PPM readings and allow you to see the correlation between the two. Although this isn’t a must-have, it can be nice to see both outputs to compare if either number is off or if one of the sensors is bad.

Can I See Flow Rates?

A proper flow meter takes the guesswork out of pool filtration. Flow rates allow you to determine proper circulation and optimize the pump speed for your pool.

The first thing you should be able to see is whether the flow is on or off. This is a very basic output, but it’s not offered with every pool automation system.

You should also have access to the flow rates for your pool. This will help you understand if you need to backwash your filtration system or if there’s a blockage. Certain components in the pump room will not work unless you have the right flow rate, so being able to monitor this number is crucial to keeping your pool system running smoothly.

Does the System Have a Water Usage Sensor?

A water usage sensor answers a simple yet important question: how much water is going into your pool on a daily basis?

A water usage sensor can alert you if the property operators are doing too much backwashing or if there’s a leak somewhere in the system. If you’re losing water unnecessarily, you’re also losing money.

These kinds of water problems will also cost you money in heating the pool. When new water enters the pool, it needs to be heated. So if you’re constantly having to replace lost water, then you’re using more thermal energy in the heater system and incurring additional costs.

Does the System Have Tank Level Sensors?

Maintaining consistent levels in large, commercial swimming pools can be extremely challenging without tank level sensors.

Without these sensors, monitoring the chemical levels for your pool becomes a manual job to be carried out on a daily basis. If your facilities are outside or in a hard-to-reach area, this is a time-consuming process, and one that can easily be overlooked.

Perhaps you have large bleach tanks and rely on an outside provider to fill them. Tank level sensors allow you to monitor the level of bleach in the tanks remotely, get insights before the tank is empty, and contact your provider to refill them, all without having someone physically check the levels inside the tanks.

What Type of Online Connectivity Do I Need?

Of all the questions to ask when choosing an automated pool system, this one may be most important. Does your pool automation controller have instant-on capabilities?

Every automated pool system promises connectivity, but many of them rely on local Wi-Fi or ethernet. The problem with these options is two-fold. First, Wi-Fi can be very difficult to access, particularly in enclosed pump rooms with cement walls. Second, very few facilities have ethernet running to their pump room 100 yards from the main building.

Instead, look for a system with instant-on connectivity through cellular. With VivoPoint, real-time access puts the pump room in the palm of your hand — anytime, anywhere.

Does the System Come With On-Call Access to Expert Support?

Managing a commercial pool is not simply a 9-to-5 job. Your guests use the amenities day and night, and equipment can break down at the most inconvenient times.

Look for a system with access to expert support that will help you in real-time to keep minor issues from becoming major problems.

At VivoAquatics, we offer chat, , and support, as well as 24/7 monitoring and notifications for all of your chemical readings via VivoPoint.

We also provide training and documentation to help you get started with your new pool system and educate any new operators who join your team. It doesn’t matter how good your automated pool system is if you don’t know how to use it!

Contact us to discuss your requirements of ph and orp controller(tl,kk,mn). Our experienced sales team can help you identify the options that best suit your needs.