Description

Top Tips for successful measurements using optical electrodes

• Use a non-fluorescent container for calibration solutions. Some plastics may fluoresce and interfere with calibration.
• Avoid strong artificial lighting during calibration. The alternating nature of artificial lights (especially fluorescent tubes) can interfere with calibration.
• Use a reasonably deep container for calibration in order to ensure a fast temperature response. The calibration solution should preferably be up to the blue line on the Probe.
• Always keep the measurement chamber and electrode lenses clean.
• Always fit the sleeve and end cap during both calibration and measurement.
• Always allow the readings to settle completely during both calibration and measurement.
• Always try to eliminate air bubbles by agitating the Probe after insertion both during calibration and measurement.
• Always calibrate and zero the electrode as close to your sample temperature as possible.
• Always zero the electrode just prior to use in clean water (bottled still mineral water is ideal).

Calibrating the Turbidity Electrode

The turbidity electrode can be calibrated at three points: Zero NTU, 20 NTU, and 1000 NTU. The Zero NTU point must always be calibrated first, followed by the other two points, all within the same calibration session. 20 NTU calibration ensures a more accurate reading at lower ranges, but may be skipped.

Zero Point Calibration

This calibration should be carried out before each day’s use.

• Step 1: Prepare Calibration Bottle. Fill a calibration bottle with clean water (bottled still mineral water is recommended). Never use sparkling or carbonated water.
• Step 2: Insert Probe. Wash the Probe in clean water, then insert it all the way into the calibration bottle. Ensure the Sleeve End Cap is fitted. Gently agitate the Probe several times to remove any clinging air bubbles.
• Step 3: Power On and Stabilise. Switch the Aquameter, or BlueLink Device, on and wait until the temperature and turbidity readings are stable. If readings are high, re-agitate the Probe to remove any air bubbles.
• Step 4: Navigate to Calibration Menu. Press the MENU key, then select “Calibration”. The screen will display calibration options including “ZERO?”, “1000?”, and “20?”.
• Step 5: Select Zero Calibration. Select “ZERO”. The Meter will display “PLEASE WAIT Stabilising” and a progress counter.
• Step 6: Complete Calibration. Once the calibration is successful, the counter will reach 100%, and “Calibrating 100% Press [OK]” will be displayed, along with the voltage output in mV. This value is not stored in the memory, so a manual record should be made. Press OK to continue.
• Step 7: Verify Zero Calibration. After calibrating, remove the Probe from the bottle, reinsert it, agitate, and allow the reading to settle. Check that the turbidity reading is within ±1 NTU of zero. If not, repeat the zero-point calibration.

Calibrating the Turbidity 20 NTU & 1000 NTU Points

These points, along with the Zero NTU point, should be calibrated when the electrode is first installed to establish its slope. A two/three-point calibrations should be carried out once a month for optimum accuracy.

• Step 1: Prepare 20 NTU Solution. Remove the Probe from the zero calibration bottle, shake off excess water, and dry the outer sleeve with a soft cloth. Pour 300ml of a fresh 20 NTU turbidity standard solution into a clean calibration cup. Gently lower the Probe into the solution all the way. Agitate the Probe several times to remove air bubbles.
• Step 2: Access Calibration Menu. Press the MENU key, then select “Calibration”.
• Step 3: Select 20 NTU Calibration. Select “20”. The screen will display “PLEASE WAIT Stabilising” and a progress counter. The Meter will wait for stability, then calibrate.
• Step 4: Complete Calibration. After successful calibration, the “Calibrating 100% Press [OK]” screen will appear with the voltage output in mV. This value is not stored in the memory, so a manual record should be made. Press OK to continue.
• Step 5: Prepare 1000 NTU Solution. Remove the Probe from the 20 NTU calibration cup, shake off excess water, and dry the outer sleeve with a soft cloth. Pour 300ml of a fresh 1000 NTU turbidity standard solution into a clean calibration cup. Gently lower the Probe into the solution all the way. Agitate the Probe several times to remove air bubbles.
• Step 6: Access Calibration Menu. Press the MENU key, then select “Calibration”.
• Step 7: Select 1000 NTU Calibration. Select “1000”. The screen will display “PLEASE WAIT Stabilising” and a progress counter. The Meter will wait for stability, then calibrate.
• Step 8: Complete Calibration. After successful calibration, the “Calibrating 100% Press [OK]” screen will appear with the voltage output in mV. This value is not stored in the memory, so a manual record should be made. Press OK to continue.

Any significant difference in the mV values to previous readings could highlight an issue with the electrode. This may just be a dirty lens, change in temperature, air bubbles or changes in the measurement chamber. Repeating the calibration after the probe has been cleaned, may resolve any issues.

Note: The 20NTU calibration point is optional and may be skipped.