How a pH meter works

ph meter

A pH meter is a precise voltmeter that measures the potential difference, in thousandths of a volt (mV), between the reference electrode and the measuring pH electrode. It's scaled in such a way that it displays not the measured potential, but converts it to a display of pH.

According to Nernst equation a standard pH electrode generates a voltage of about 59 mV per pH, and at pH 7 (neutral pH) the electrode produces 0 volts. Acids produce positive and bases negative voltages.


Sensitive measurements

The glass electrode has a very high internal resistance, typically of the order of 100 MOhm. To be able to make reliable potential measurements the input resistance of the pH meter should be at least 10000 times larger than the resistance of the sensor.

A high-resistance (low current) measurement easily gets noisy, because it is sensitive to temperature changes, electrostatic charges and electromagnetic noise. Noisy readings prevent accurate measurements and reduce the effective resolution. To measure one thousandth of a volt (mV) requires a really good high-resistance voltmeter.

Compensation algorithms

Temperature impacts pH electrode performance. To facilitate your measurements your pH tester needs to have a temperature compensation function.

Temperature also has an impact on your measured solution. A solution temperature compensation function is beneficial for many applications.

Types

There are three different types of pH meters: portable, bench and in-line.

• Portable devices are great when you need to perform measurements outside the laboratory. Portable pH tester should be ergonomic, rugged and versatile.

• Bench tester is usually more precise and has more options. They are typically used in a laboratory where an interface for data communication and advance measurement features are important.

In-line pH transmitters for process control are designed to with stand harsh environments.

Calibration

A pH tester needs to be calibrated in order to correct for any deviation of the electrodes from their ideal behavior.

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History of the pH Meter 
The first commercial pH testers were built around 1936 by Arnold Beckman in the United States and by Radiometer in Denmark. However, glass pH electrodes …

Automatic buffer recognition 
If possible, choose a pH meter with a "Automatic buffer recognition" feature. This feature will help you to avoid errors during calibration. A pH meter …

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