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Almost all pH sensors are designed to produce a 0 mV signal at neutral pH of 7 with slope of 59,16 mV/pH at 25 °C. This theoretically ideal slope represents sensitivity and the point usually represents what is called an isopotential point, where potential is constant with temperature changes. When isopotential point is known, it can be used together with theoretical knowledge of electrodes behavior, allowing correction of the pH measurement at any temperature by comparing it to the reference temperature. [2]
Picture 1 Reference electrode and measurement electrode
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Sensors measuring pH should be on for at least 30 minutes, depending on the sensor, to ensure that all components are at thermal equilibrium and the calibration solution used should be immersed for atleast a minute to ensure equilibrium [5].
Picture 2 Graph showing older pH sensors offset
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Industrial-grade pH sensors are typically mounted on special mounts to allow wider range of use in different applications [3]. Different mounts give option for installing the sensor submerged, so that liquid flows through it or so that they are inserted into the liquid when needed. Instruction manuals on this kind of sensors provide various different values and specifications to help determine operability in process conditions. Typically at least measuring range, sensitivity, stability, temperature range, pressure range and weight are quickly and easily obtainable from manuals. Sometimes industrial sensors contain preamplifiers that are installed as close to the sensor unit itself for easier calibration work and cables of these sensors are well protected with single shielding etc. [3].
Picture 3 Cable of industrial pH sensor
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