Hanna Instruments HI520 - Page 120

Measuring with pH & ORP Probes 120
The probe should be calibrated:
• Before installation
• Whenever the probe is replaced
• When higher accuracy is required
• After periodic maintenance
• After calibration TimeOut has expired
21.4.1. pH Probes Calibration
HI520 process controller allows two types of pH calibration procedures:
• Standard calibrations performed in standard buffer solutions
` Hanna Instruments: 1.68, 4.01, 7.01, 10.01, 12.45 pH
` NIST: 1.68, 4.01, 6.86, 9.18, 12.45 pH
• Process calibrations performed with probes calibrated in standards and installed in the process.
Note: See 6.2 Probe Settings, General Parameters section for TempOffset section.
Preparation Guidelines
Calibrations performed in standard buffers follow the preparation guidelines detailed below.
• Pour a minimum 50 mL of the buffer solutions into clean beakers.
If possible, use plastic beakers to minimize any EMC interferences.
• For accurate calibrations and to minimize cross‑contamination, use two beakers for each buffer solution:
one for rinsing the probe and one for calibration.
• On the controller, go to Channel setup, Probe Setup, Cal.Buffer Group to select buffer group.
• Up to three pH buffers may be used for a calibration.
At least two buffers are required to determine a pH slope.
Note: It is recommended to select buffers that bracket the expected process pH.
pH Standard Calibration
One‑, two‑ or three‑point calibration can be performed using one of the buffer solutions selected from one of
the two groups.
It is generally recommended to use 7.01 or 6.86 pH buffer as first calibration point.
When the electrode is immersed into buffer solution, the controller automatically recognizes the buffer value.
One‑Point
1. Press CAL, to enter calibration mode.
2. At prompt, with the password enabled, input the passcode.
3.
The first suggested buffer solution “7.01 pH” (if using Hanna Instruments buffer group) or “6.86 pH” (if
using NIST buffer group) is displayed in the upper left of the display window.
4. Immerse the pH probe approximately 4 cm (1½”) into buffer solution and stir gently.
The controller automatically recognizes the standard and the recognized buffer value is displayed on the LCD.