Hanna Instruments HI 99191 portable pH meter for low ionic strength water

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The Hanna Instruments HI 99191 is a waterproof portable pH/temperature meter designed specifically for measuring the pH of drinking water, since the pH of water influences properties including taste, odour, clarity and disinfection.

Measuring the pH of water low in minerals is difficult using a general-purpose pH meter. The lower the mineral content, the less conductive the water will be. Low conductivity water presents a challenge since the pH meter is an electrochemical system that relies on the test sample being conductive. 

To overcome this challenge, the product uses the FC 215 amplified pH electrode. The electrode has three ceramic junctions in the outer reference cell providing electrolyte flow of 40-50 µL/h. This increased flow provides a greater continuity between the reference electrode and the indicating electrode, making it suitable for water of low ionic strength. To optimise the flow from the electrode, the refill cap should be screwed to open, allowing positive head pressure to be created.

The meter has automatic 1- or 2-point calibration, automatic temperature compensation and BEPS (battery error prevention system), which alerts the user in the event that low battery power could adversely affect readings. % battery power is also shown at start-up. With a multilevel LCD display and on-screen tutorial messages for calibration and set-up, the compact unit is waterproof and easy to clean.