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How much do you know about the ph water quality sensor probe

What is a ph water quality sensor probe?

The pH water quality sensor probe contains two electrodes (sensor electrode and reference electrode) for measuring the hydrogen ion activity in the solution. The ion exchange generates a voltage, which is measured by a pH meter, which converts the voltage to a readable pH value. It is a water quality sensor that measures the pH of a liquid.

Measuring pH with pH water quality sensor probes is important to a wide range of industries, which is why there are different pH sensors for different applications. Next we'll look at how a pH probe works, what a pH sensor measures, and what's inside a pH probe.

PH meters
PH meters

What do ph water quality sensor probes measure?

A pH meter uses a pH water quality sensor probe to measure the acidity or alkalinity (hydrogen ion activity) of a solution, expressed as a pH value. The pH of a solution is related to the ratio of the pH probe to the hydrogen ions in the solution being measured.

When you dip a pH probe into a solution, many hydrogen ions move towards the glass electrode, displacing some of the metal ions inside, and some of the hydrogen ions disperse into the solution being measured. This ion exchange process is called ion exchange and is the main principle behind how the glass electrode inside the pH probe works.

Ion exchange also occurs on the inner surface of the glass electrodes. Because the acidity of potassium chloride inside the electrode is different from the acidity of the solution to be measured, the activity of hydrogen ions will be different, resulting in different charges. When this happens, a potential difference is created across the glass electrode and the reference electrode, which produces the pH reading on the meter.

While the meter measures voltage, the digital display shows it as a pH measurement. It is calculated from a voltage difference; the greater the voltage between the pH probe (electrode) and the solution being measured, the greater the difference in hydrogen ion activity. The more hydrogen ion activity that occurs, the lower the pH and vice versa.

Calibration of ph meter is very important

Before using a pH meter, it is important to calibrate it for accurate results and is an important part of general electrode maintenance. We recommend that you follow our pH probe calibration recommendations to always ensure your pH readings are reliable.

To gain a deeper understanding of the function of a pH probe, we need to first understand how the pH electrode inside the pH probe works.


How do pH electrodes work?

There are various types of pH electrodes suitable for industrial and laboratory applications, however, most of them are made of glass and therefore break easily and require hydration. That's why we ship each pH probe in a plastic immersion bottle filled with the pH probe storage solution.

The first pH electrode invented consisted of a glass bulb filled with a strong electrolyte with an inner silver/silver chloride (Ag/AgCl) half-cell and a silver wire in contact with the outer solution.

The general working principle of pH electrodes has not changed much, but as technology advances, combination electrodes and double junction electrodes are more commonly used.

What is a combined electrode

Combination electrodes measure on both sides of a glass electrode and are the most common pH probes. A pH probe requires an electrode with a closed circuit to measure the potential through the solution inside the electrode (such as potassium chloride), the solution being measured outside, and the pH meter.

When the electrode is immersed in a test solution, it recognizes the positive charge of the hydrogen ion in millivolts (mV) and transmits a signal to the internal electrode. Silver wires inside the pH probe carry the electrical signal to the electrode cable that connects to the pH meter.

Components of a pH Probe

Most pH probes consist of a glass hydrogen ion sensitive electrode and a reference electrode, called a combination electrode. Common pH electrodes consist of a variety of structures.
·Electrode body
·glass film
·Reference electrode
·Reference electrolyte
· Reference knot

The electrode body can be plastic or glass, so when you hear the term "glass electrode" it refers to the membrane material, not the outer electrode body.
Laboratory Grade pH Probe: Extruded epoxy resin body makes it incredibly resistant to strong acids and bases.
Industrial pH Probes: The sensor body makes it chemically inert and virtually indestructible.

Glass Membrane:

The glass film is a Ph-sensitive film filled with buffer solution, located inside the glass electrode of the pH probe. The membrane allows continuous bonding of hydrogen ions within the membrane. The outside of the glass film is exposed to the sample under test. It is the difference in hydrogen ions across the membrane that generates the voltage potential.

The shape of the membrane can vary depending on the application. Certain applications require pH probes with specialized membranes that can be used to pierce semi-solid media, such as spear-tip pH probes.

Reference Electrode:

A reference electrode is required to provide a constant potential within the pH probe to determine pH. The most common type of reference electrode consists of silver/silver chloride (Ag/AgCl), which is used in a variety of applications including the medical and food industries because it is non-toxic to humans.

Reference electrodes containing mercury chloride (Hg/Hg2Cl2) are still used in some industries, but are no longer commonly used due to the toxicity of mercury.

The latest reference system to be developed contains iodine due to the fast response time and low temperature sensitivity. The iodine reference frame is often used when measuring the pH of tribuffer and protein solutions. Because it's a metal-free ion system. Reference electrodes containing metal ions (such as Ag/AgCl) can interact with the solution to block the reference contact.

Reference Electrolyte:

The reference electrolyte closes the electrical circuit within the pH probe electrode. Electrolytes must be chemically neutral and have good electrical conductivity to work properly.

The fluidity of the electrolyte solution is also important. Because the different diffusion rates of hydrogen ions in the electrolyte solution can create a potential, which can cause problems when measuring pH.

The most common reference electrolyte solution is potassium chloride (KCl). However, KCl is not recommended for measuring pH in low temperature solutions. Because it crystallizes inside the pH probe.

Reference Junction:

The reference junction, also known as the diaphragm, is a porous junction that creates an electrical current between the reference electrode and the sample under test. Different reference junctions have different discharge rates depending on the application you are using. Double junction electrodes are used to operate under adverse conditions in applications where reverse electrolyte flow may occur. When the measured solution is acidic or alkaline, or under extreme pressure or high temperature, electrolyte backflow may occur.

The double junction electrode protects the reference junction from contamination. Because the solution to be measured must be diffused through two junctions before pH can be recorded.


The work of the pH water quality sensor probe depends on the exchange of hydrogen ions that generate a voltage. The glass electrode inside the pH probe measures the difference in pH between the pH electrode and the solution you are testing. The electrodes do this by measuring the voltage difference between the electrodes and the hydrogen ions produced in solution. It is the pH meter that converts this voltage into a readable pH value.

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