09/09/2019 | pH | 9 MINUTE READ

Types of pH Sensors: What You Need to Know


A pH sensor is one of the most essential tools that’s typically used for water measurements. This type of sensor is able to measure the amount of alkalinity and acidity in water and other solutions. When used correctly, pH sensors are able to ensure the safety and quality of a product and the processes that occur within a wastewater or manufacturing plant.

In most cases, the standard pH scale is represented by a value that can range from 0-14. When a substance has a pH value of seven, this is considered to be neutral. Substances with a pH value above seven represent higher amounts of alkalinity whereas substances with a pH value that’s lower than seven are believed to be more acidic. For instance, toothpaste typically comes with a pH value of 8-9. On the other hand, stomach acid has a pH value of two.

The difference between an alkaline substance and an acidic substance is very important for any company that uses a cooling tower, boiler, manufacturing processes, swimming pool control, and various types of environmental monitoring. The human body has a standard pH level of 7.4, which is essential for the body to run effectively. If the composition of the body every becomes too acidic or overly alkaline, it will look to return to the neutral state.

manufacturing plant

No matter what application you’re using it for, a pH sensor will allow you to keep pH levels at a level most ideal for the process. This could be anywhere from strong acids to caustics. There are many different types of pH sensors that you can obtain for your application in the course of  liquid measurement; these could include combination pH sensors, laboratory pH sensors, process pH sensors, and differential pH sensors.

  1. A combination pH sensor uses a reference electrode and a measuring electrode. The reference electrode is used to provide a stable signal, while the measuring electrode is designed to detect any changes that have occurred with the pH value.
  2. Differential sensors are comprised of three distinct electrodes, the third of which is a metal ground electrode. These sensors are unique in that they can prevent reference fouling.
  3. Laboratory sensors can be made with combination sensors that are contained within plastic bodies and 12mm glass. These sensors are designed for lighter applications such as pool monitoring and environmental sampling.
  4. Process pH sensors are made from combination sensors but built in large and durable bodies that contain a process connection for continuous pH monitoring.

Different pH sensors are built for different applications, which you should fully understand before purchasing one of these sensors.

pH Sensors for Quality Water

drinking water bottle

A pH sensor helps to measure the acidity or alkalinity of the water with a value between 0-14. When the pH value dips below seven, the water starts to become more acidic. Any number above seven equates to more alkaline. Each type of pH sensor works differently to measure the quality of the water. The pH of water can help determine the quality of water. Measuring the pH can also provide indications of pipe corrosion, solids accumulation, and other harmful byproducts of an industrial process.

In an environmental setting, the changing pH could also be an early indicator increasing pollution. If the pH level reaches above 8.5, the water would be considered hard, which would likely cause scale development in boilers and pipes. As aforementioned, there are four main types of pH sensors that you can select from, which include combination sensors, differential sensors, laboratory sensors, and process sensors, each of which is suitable to different applications.

Combination pH Sensors

laboratory liquid

A combination pH sensor is by far the most commonly used sensor available, which is mainly because this type of sensor can act as the base for the creation of laboratory sensors and process sensors. This electrochemical sensor is outfitted with two different electrodes, which include a reference electrode and a measuring electrode. While the reference electrode focuses on keeping the signal stable when you record the pH level, the measuring electrode will identify if there have been any recent changes in the pH level.

At Sensorex, the technology with combination pH sensors is primarily used for the creation of laboratory and process sensors. The best aspect of this type of sensor is that the technology is highly versatile. The two electrodes are able to provide the most important functions of reading and measuring the pH levels of water, which ensures that you’re provided with quick and accurate measurements.

Differential pH Sensors

Differential pH sensors work somewhat differently than combination pH sensors in that they come equipped with three electrodes. While the first two electrodes are the same as the ones used in combination sensors, the third one is a metal ground electrode that can be very beneficial for the prevention of reference fouling. This type of sensor is considered to be a heavy-duty sensor because of its third electrode.

While it’s possible for a standard pH sensor to become contaminated whenever the pH levels change, the usage of a third electrode acts as a buffer for the measuring electrode, which ensures an accurate reading even when contamination occurs. As such, these sensors should hold up for longer and are ideal for tough wastewater and industrial applications.

SD7420CD Differential pH Probe There are three main series of differential sensors that you can purchase, which include the SD7000 series, the SD7420 series, and the SD7500 series. Each sensor offers reliable results and a range of additional features that should prove useful when measuring the quality of your water.

Laboratory pH Sensors

Laboratory pH sensors use combination pH sensor technology but are housed in plastic bodies and 12mm glass. These lightweight sensors are perfect for light applications, which can include research and education, pool monitoring, and environmental sampling. The versatility of these sensors are fantastic. If you’re searching for a laboratory sensor, the junctions, cables, and sensor fill can be customized to fit the exact application needs that you have.

pH1000 Polycarbonate Laboratory pH SensorWhen searching for the right laboratory sensor, the three categories of sensors available to you include basic, advanced, and research. Basic sensors like the pH1000 are durable yet easy-to-use, which makes them ideal for use in swimming pools, aquariums, and hydroponics. Advanced sensors such as the pH2000 can be used for a variety of different sample types, which makes them perfect for wastewater and environmental sampling. Finally, research-grade sensors like the pH3000 are best for low ionic samples, which include drinking water and pharmaceutical applications.

Process pH Sensors

Process pH sensors use combination sensor technology in larger and more durable bodies. These sensors are also outfitted with a process connection, which makes them very suitable for the continuous monitoring of the pH levels of your water. Because of the high durability of these sensors, they can be placed into a tank or mounted directly into a pipe. Whether you want to use the sensor for industrial source water, process water or wastewater monitoring, the three categories of process sensors include moderate sensors, moderate to heavy-duty sensors, and heavy-duty/coating sensors that can be configured with a flat bulb glass, which many consider a self-cleaning design.

SD7000 Series

If you want to eliminate ground loop error with a differential measurement technique, the heavy-duty SD7000 series is right for you. The moderate to heavy-duty S8000 series allows for quick cartridge replacement and very economical upkeep. Finally, the moderate S272CD sensor comes with integrated cable assembly for easy use. To determine which of these sensors is right for you, it’s important that you first identify what your pH measurement needs are.

The Importance of Quality Water Systems

The quality of the water that you use during various industrial processes is essential for the quality of services and goods that you provide, which means that your ROI can be directly affected by poor water quality. Managing the quality of your water via different systems is also a critical aspect of complying with strict environmental, industry, and safety standards.


When looking specifically at water pre-treatment for manufacturing purposes, this type of water quality management allows you to remove impurities from intake water before this water is used in a variety of different manufacturing processes. When these impurities are removed, operations efficiency will be improved, heating and cooling will be more efficient, and you’ll be able to more effectively maintain compliance with necessary water quality standards. If you have a good monitoring system in place, the benefits can be numerous and may include:

  • Reducing water waste
  • Saving energy
  • Meeting sustainability requirements for your supply chain
  • Preventing downtime
  • Maintaining a healthy workplace for your employees
  • Reducing the use of hazardous chemicals

For the everyday consumer, poor water quality can create health concerns, dull hair, rough clothes, and skin that’s dry and itchy. A pH sensor plays a very important role in water quality and water treatment. When the pH value of a water treatment plant becomes too high or too low, the water can be hazardous.

Keep in mind that pH fluctuations are also very costly to fix. Extra amounts of chemicals will need to be used to get rid of the waste, which leads to excess downtime and higher expenses. In a standard wastewater facility, a pH value of 6.5-8.5 is considered to be in a neutral range.

Keeping your water at this level and continuously monitoring pH levels should help you keep costs down. However, it’s important that you use different pH sensors to get the best water quality. For instance, the use of a third electrode in differential sensors makes this sensor perfect for a variety of industrial applications such as wet scrubbers.


Understanding the differences between the various types of pH sensors can play an important role in your company. If you require continuous monitoring of pH levels in a tank or pipe, it’s essential that you choose an industrial sensor as opposed to a lightweight lab sensor.

The aforementioned guide should assist you in making the right choice, which will save you time and money in the future. For more information about pH or smart water sensors, make sure that you view our products or get in touch with one of our team members here at Sensorex!

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Posted by Dominic O'Donnell on September 9, 2019

Sensorex is a global leader in the design and manufacture of quality sensors for water quality and process applications. The company offers more than 2000 sensor packages for pH, ORP, conductivity, dissolved oxygen, free chlorine, chlorine dioxide, UV transmittance and other specialty measurements, as well as a full line of sensor accessories and transmitters. Its expert technical support engineers solve analytical sensor challenges with custom designs and off the shelf products.

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