Oyster10-en-US_v2.3 9/15
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pH Overview
pH is a unit of measure (ranging from 0 to 14pH) indicating the degree of acidity or alkalinity of a
solution. pH tests are the most commonly performed measurements in water quality testing, using
the hydrogen ion activity of a solution to determine acidity or alkalinity. Solutions with a pH less than
7 are considered acidic, solutions with a pH higher than 7 are known as bases, and solutions with a
pH of exactly 7 are considered neutral.
The pH scale is logarithmic, so, for example, if sample A is 1 pH less than Sample B, this means
that Sample A is 10 times more acidic then Sample B. A difference of 1 pH represents a ten-fold
difference in acidity.
ORP/REDOX Overview
ORP stands for
O
xidation
R
eduction
P
otential and represents the oxidizing or reducing nature of a
solution. The overall “reactive” tendency of a solution can be determined from ORP measurements.
ORP testing is becoming more common in waste-water and water treatment measurement
regimens. The unit of measurement for ORP is mV.
Calibration and Operation
pH Calibration (ORP does not require calibration)
Before accurate measurements can be made, it is necessary to perform a
3-point calibration
of the
meter with its electrode. Calibrate to a pH 7 buffer first, followed by a pH 4 (or 1.68) buffer and then
a pH 10 (or pH 12.45) buffer. The meter automatically recognizes the buffers listed in the table
below and calibrates itself to the buffer’s pH value.
1. Connect the pH electrode to the meter’s BNC connector input.
2. Open the top half of the meter to an appropriate viewing position.
3. Power the meter with the
POWER/CAL
button.
4. Place the electrode into a buffer solution.
5. Press and hold the
CAL
key until the CAL display icon appears.
6. During calibration, ‘CAL’ is shown on the display followed by ‘SA’
(saved).
7. When calibration is complete, the meter automatically displays ‘END’ and returns to the normal
operation mode. Repeat steps 1-5 as necessary. Note that it is not necessary to turn the meter
off and then back on again to calibrate each reference.
Error Message Note
: The meter will display ‘E13’ if a calibration step fails. Try the calibration again
if ‘E13’ is displayed. The most common reason for the error is inaccurate or stale buffer solutions.
pH reading
Range of measurement
1.68
0.00 to 1.68
4.00
1.68 to 6.50
7.00
6.50 to 7.50
10.00
7.50 to 12.45
12.45
12.45 to 14.00
Electrode note:
Since pH electrodes can vary in performance, this meter displays an electrode’s
slope in %. For example, if two electrodes (one new and one moderately used) are calibrated in the
same pH 4 solution they’ll both display pH 4 on the meter. This is because the meter will accept one
pH value for a range of measurement values as shown in the table above (in this case, any reading
between 1.68pH and 6.50pH will be accepted as 4pH calibration). The meter then displays the
slope % for the electrode under test. If the slope % is below 75% or above 125%, the electrode
must be replaced. A slope of 100% is ideal.
