Metex 8760CLP Total Free Chlorine & pH Analyzer - Manual (Page 36)

AQUAMETRIX INC.
1-800-742-1413 www.aquametrix.com
36
pH CALIBRATION
The pH input is calibrated using one of two methods. A one-point standardization adjusts the electrode
offset while maintaining the previous slope. The two-point calibration combines the results of the
standardization with the results of
the buffer 2 calibration and
calculates the slope as well as the
offset.
A calibration is easily
accomplished by selecting an
appropriate buffer, placing the
electrode in the buffer solution, and
letting the analyzer do the rest.
The analyzer tests for electrode
stability and performs many
diagnostic tests during calibration.
Automatic stability testing takes
most of the guesswork out of
deciding whether a reading is
acceptable or not. The internal diagnostic tests will activate caution or error messages if faulty operation
is suspected or detected. Errors detected during calibration will not cause the analyzer to lock up.
Buffers automatically recognized by the 8760CL are:
Buffer Part Number, 500 mL bottle
4.01 pH, red A35-13
7.00 pH, yellow A35-14
10.0 pH, blue A35-24
Selecting a pH Buffer
pH buffers provide the simplest and most accurate method of calibrating the pH sensor and analyzer.
First Buffer: The first step is to use 7 pH buffer to calculate the mV offset of the electrode from the
theoretically perfect 0 mV. pH 7 buffer is used because it simulates 0 mV thus making it the best standard
since the electronics are also at this 0 mV reference point.
Second Buffer: The next step in the calibration is to use a second buffer (usually 4 pH or 10 pH). When
choosing which buffers to use in calibration, it is best to select buffers that fall on both sides of the normal
operating pH range. By using these two buffers, the slope calculation will encompass the normal pH, thus
giving the most accurate pH measurement. Either of these buffers, pH 4 or pH 10, gives a large enough span
relative to the pH 7 buffer that a good slope can be calculated. When performing the two point calibration, a
percent value will be given in microprocessor based pH analyzers. The closer to 100% the slope is, the better
the efficiency and thus the performance of the electrode.
The model 8760CLP has been programmed to recognize the three buffers most commonly used for
calibration: pH 4, pH 7, and pH 10. To achieve greater accuracy, the temperature compensated values
for these buffers are calculated by the analyzer. Simply place the electrodes in the buffer solution and
the analyzer will select the correct buffer value, allowing for an offset of up to ± 1.3 pH units.
NOTE: [Auto] must be selected in the calibration menu for this feature to work.
Illustration: 30 pH menu