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pH meter, electric device used to measure hydrogen-ion activity (acidity or alkalinity) in solution. Fundamentally, a pH meter consists of a voltmeter attached to a pH-responsive electrode and a reference (unvarying) electrode. The pH-responsive electrode is usually glass, and the reference is usually a silver–silver chloride electrode, although a mercury–mercurous chloride (calomel) electrode is sometimes used. When the two electrodes are immersed in a solution, they act as a battery. The glass electrode develops an electric potential (charge) that is directly related to the hydrogen-ion activity in the solution (59.2 millivolts per pH unit at 25 °C [77 °F]), and the voltmeter measures the potential difference between the glass and reference electrodes. • • Calibration depends on the required measurements as well as application areas concerned. It is important to calibrate/adjust a pH meter (technically speaking to calibrate the pH electrode in the pH meter’s sensor) sooner or later, depending on how accurately we want it to measure. The article explains the process of calibrating a pH meter and which sensor should we use depending on the application required. • For example, the accuracy of the measurement is very critical in industries like Life Science. As such, here, it is required to measure pH at regular intervals. On the other hand, in a wastewater treatment plant, since the pH of water in applications doesn´t change at a rapid rate when compared to the Life Science industry, calibration is not that critical. • What is pH meter calibration? • If we calibrate a pH meter, then we measure the value you receive in a known solution, usually a pH buffer, and control the difference. If we adjust a pH electrode, then we correct its current measurement value to a reference value, usually the one printed on the buffer bottle. • We commonly do the second point, adjustment, but we call it calibration. Before we start, make sure the transmitter signal won’t cause issues in your process when you disconnect it. Also, make sure you program your transmitter for the buffer solution(s) you use. • Speaking of which, we should have the following supplies: • Cleaning solution • Distilled water • Clean beakers • Buffer solution that you trust (two is better if you have another) • Paper towels • To know more about common errors with pH sensors, take a look at this article • How to calibrate a pH meter • 1. Examine the pH electrode • First, check the pH electrode for contamination or damage. If it’s damaged, then fix it or toss it. If it’s just dirty, then use the cleaning solution according to its directions. Whether we use acids, washing liquid, or alkali, choose a solution appropriate for your process and the contamination. • 2. Flush the pH sensor • Next, flush your sensor with distilled water. We can do this, even if we didn’t have to clean it, to rinse away anything that may contaminate the buffer solution you’ll use in Step 3. After flushing, dab or pat away excess water with the paper towels. We should not generally rub it more: you might charge or damage the sensor. • 3. Immerse the pH electrode • Fill a beaker with your first buffer solution, then immerse your electrode in it. It’s easy to just drop the sensor directly into the buffer bottle, but we can avoid contamination and extend the life of a buffer if we use the beaker. • 4. Calibrate the pH meter • Now we can start your calibration/adjustment. Keep an eye on the stability of the value; an old pH meter might react sluggishly. When the value stabilizes, set the device to accept this calibration/adjustment point. • 5. Rinse the pH sensor and repeat • Flush the pH sensor with distilled water again, then immerse it in another clean beaker with the second buffer solution. • How often do we need to calibrate a pH meter? • How often we need to adjust the meter depends on the following: • Accuracy required by the process • Stress the process conditions put on the sensor • Sensor’s ability to withstand that stress • In a drinking water application, we can expect stable conditions, so we may only need to calibrate once a month. A measuring point with a high temperature or high pH might need a weekly tweak. We can use experience – or borrow someone else’s – and pay attention to the diagnostics the system provides. • Adjustments in the field sometimes come with environmental challenges. However, digital sensors make maintenance much easier. In many cases, the microprocessor that converts the signal can do more, like store the adjustment values in its memory. That way, we can bring the sensor into a lab or workshop, connect it to a suitable device, and perform an adjustment. Then we can either reinstall it or set it aside as a nicely adjusted backup. • #phmeter #phs-3c #calibration #calibrationofphmeter #yokephmeter #
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