Thermo Scientific Orion Star A320 Series Manual page 35

Thermo Scientific
Buffer Group Setting
Orion Star A321 pH meters, Orion Star A325 pH/conductivity meters and Orion Star A326
pH/RDO/DO meters are capable of automatically recognizing pH buffer values within the
selected buffer set during a pH calibration. During the pH calibration, the meter uses the
selected pH buffer set and the raw mV reading of the pH electrode in the buffer to recognize
and display the buffer value at the measured temperature. The raw mV reading of the pH
electrode in the buffer must be within one pH unit (approximately ±59 mV) of the buffer's
theoretical mV value for the meter to recognize the buffer.
USA Buffer Set
pH Buffer mV range
1.68 +255 mV to +374 mV
4.01 +117 mV to +236 mV
7.00 -59 mV to +59 mV
10.01 -237 mV to -119 mV
12.46 -382 mV to -264 mV
Testing a pH Electrode for Automatic Buffer Recognition
Use the following procedure to verify that the raw mV reading of the pH electrode is within one
pH unit (±59 mV) from the theoretical mV reading of the pH buffer, and therefore verify that the
pH electrode in use is capable of performing automatic buffer recognition.
1. Prepare the pH electrode according to the electrode manual. Set the meter measurement
mode to mV.
2. Rinse the pH electrode with distilled water, blot it dry with a lint-free tissue and place the pH
electrode into a pH 4.01 buffer at approximately 25 °C.
3. Wait for the measurement to stabilize and record the mV value of the pH 4.01 buffer when
the measurement is stable.
4. Remove the pH electrode from the pH 4.01 buffer.
5. Rinse the pH electrode with distilled water, blot it dry with a lint-free tissue and place the pH
electrode into a pH 7.00 buffer at approximately 25 °C.
6. Wait for the measurement to stabilize and record the mV value of the pH 7.00 buffer when
the measurement is stable.
7. The mV reading of the pH electrode in pH 4 buffer should be +117 to +236 mV and in pH 7
buffer should be -59 to +59 mV. If the mV readings are in the correct ranges, the pH
electrode is capable of performing automatic buffer recognition. If the mV readings are not
in the correct ranges, manually enter the pH buffer values during a pH calibration.
Chapter 3
DIN Buffer Set
pH Buffer mV range
1.68 +255 mV to +374 mV
4.01 +117 mV to +236 mV
6.86 -51 mV to +67 mV
9.18 -189 mV to -70 mV
Orion Star A320 Series Portable Meter User Manual
Meter Setup Menus
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