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Concerns in pH # 1: Heat Effect on the Slope

IC. CONTROLS. Concerns in pH # 1: Heat Effect on the Slope. PROBLEM. At 25ºC the slope of a 100% efficient probe is 59.16 mV per pH unit with 0 mV starting at pH 7. As the temperature changes, so does the mV per pH unit as seen on the graph on the next slide.

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Concerns in pH # 1: Heat Effect on the Slope

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  1. IC CONTROLS Concerns in pH # 1: Heat Effect on the Slope

  2. PROBLEM At 25ºC the slope of a 100% efficient probe is 59.16 mV per pH unit with 0 mV starting at pH 7. As the temperature changes, so does the mV per pH unit as seen on the graph on the next slide. Therefore if the temperature is not compensated false pH measurements will result.

  3. Temperature vs mV/pH Unit

  4. Temperature Effect As seen on the graph, temperature has no effect at pH 7. The further from pH 7 the process is, the larger the effect temperature will have. The millivolt output increases 0.1984 mV per degree Celcius.

  5. Temperature Effect Example: At 60°C mV/pH unit is (60°C - 25°C) x 0.1984 mV + 59.16 mV at 25°C = 66.10 mV/pH Unit If pH is 4, sensor should output (7 - 4) pH Units x 66.10 mV/pH Unit = 198.30 mV If the analyzer is compensating at 25°C the mV/pH unit is 59.16 and pH would be calculated by the analyzer as: 198.30 mV ÷ 59.16 mV/pH Unit = 3.35 pH units The analyzer will read 7 - 3.35 = 3.65 or a 0.35 pH unit difference from the true value at 60°C.

  6. Temperature Effect Slope Changes with Temperature The Further from pH 7 the Greater the pH Effect Temperature Compensation is Critical to accurate pH Measurement Proven Technology Superior Design Better Results

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