What is a pH Meter and how does it Work?

pH is a measurable parameter between the values of 0 and 14, provided the concentration of the solution does not exceed 1M. Solutions with a pH<7 are acidic, whereas those with a pH>7 are alkaline. A PH METER is a device that measures the changes in the activity of hydrogen ions in a solution.

pH meters
pH meters are electronic devices comprised of a special measuring probe (a glass electrode or, an ion-selective field-effect transistor (ISFET), in specialized cases), attached to an electronic meter that displays the decimal pH reading. The Automatic Calibration PH Meter must be calibrated prior to use against buffer solutions of known hydrogen ion activity.

The standard methodology for measuring pH
Combined PH meters consist of a glass electrode made of a specialty glass membrane that is sealed at the end forming a bulb. Inside the glass is an internal standard acidity solution, usually 0.1 M HCl, along with an internal reference electrode, REin (typically an Ag/AgCl wire electrode). This solution is called the reference solution of known pH, 7.
A second electrode REext is placed in an external tube immersed in KCl. This external tube forms a concentric enclosure around the first enclosed glass tube containing the 0.1 M HCl (the internal tube).
The external tube is made of pH-sensitive glass and is in contact with the test solution through an opening called a porous diaphragm. The inclusion of a reference electrode encased by the internal tube is necessary as its pH is known and can be compared to a test solution so that its pH value can be determined. This set-up is called a combination pH electrode.

Operation of pH meter
The 3 in 1 PH Meter operates like a voltmeter. The pair of electrodes in the combinatorial set-up can measure small changes in voltage (also called potential difference) in the order of millivolts. Changes in potentials are caused by the loss of electrons that correspond with the loss of H+.

Calibration
The pH meter should be calibrated before each measurement using at least two standard buffer solutions of known pH values (typically around 4 and 7).

What is a TDS meter?
A TDS Meter is a small hand-held device used to indicate the Total Dissolved Solids in a solution, usually water. Since dissolved ionized solids, such as salts and minerals, increase the conductivity of a solution, a TDS meter measures the conductivity of the solution and estimates the TDS from that reading.
TDS meters may be referred to as TDS testers or PPM (parts per million) testers, but all of these are different names for the same thing. TDS meters can be purchased for as low as $10, but more advanced models can cost $1,000+ based on the level of accuracy and additional features offered.
For example, a basic TDS meter may only measure the amount of total dissolved solids in a solution while an advanced model may be able to check salinity, temperature, and more.

DO Meters use an electrochemical, polarographic, amperometric, galvanic, or optical sensor to measure the amount of gaseous oxygen dissolved in a water sample. DO is an important water quality parameter that effects marine life, the taste of drinking water, and the corrosiveness of a water sample. Common applications include groundwater remediation, wastewater, aquariums, and fish hatcheries.

Salt Meters are an easy-to-use water quality indicating tool and are a great way to obtain a quick estimate of the dissolved salt present in a wide range of water samples.
They are useful in a wide range of applications from testing salinity levels in water used for agriculture, drinking water, wastewater, and for testing the water in home pools and spas.
If you have an interest in knowing how a salinity meter works, this article is for you.
About Salinity Meters
Salinity Meters are devices that are used to measure the amount of salt present in a substance.
You can purchase salinity meters either on their own or as a sensor in multiparameter meters, which can measure other water quality parameters such as pH, conductivity, TDS and more.

Conclusion
The inner workings of salinity meters may seem complex, but they produce accurate salinity measurements in a matter of seconds. When looking for a salinity meter, it is important to check whether the units of measurements are suitable for your requirements and choose a device with automatic temperature compensation (ATC) to make measuring faster and easier.