The WQ-DO sensor requires only a 1-point calibration. Calibration is performed in a 100% saturated dissolved oxygen environment (Air Calibration) or in a known dissolved oxygen concentration solution (In-Situ Calibration). In order to ensure proper polarization of the electrodes, the probe must warm up for 15-30 minutes before calibrating. 30 minutes is recommended.

The dissolved oxygen sensor should be calibrated as often as possible. Each day before use is recommended. Calibration drift can be checked by immersing the probe in a 100% saturated environment. If the value has changed significantly since calibration, recalibrate.

During air calibrations, the 100% saturation value will change according to corresponding barometric pressure and salinity values.  The saturation value falls below 100% at lower barometric pressures and higher salinities.  For instance, when the barometric pressure drops to 745 mmHg, the “100% saturation value” will drop to around 98%.  For the most accurate readings, salinity and barometric pressure readings can be set in the Settings tab.

 

WQ DO set barometric pressure in settings tab

Figure 1: Set the Barometric Pressure in the Settings tab

To see how salinity and temperature affect the Dissolved Oxygen reading, click on the Library tab, select Environmental and then Dissolved Oxygen Solubility. At 25 degrees Celsius, the difference of Oxygen in mg/L can differ as much as 1.5mg/L from freshwater (0 ppt salinity) to salt water (~35 ppt salinity).

 

At 25C, difference of Oxygen in mgL can differ a lot from freshwater to salt water

Figure 2: At 25C, the difference of Oxygen in mg/L can differ as much as 1.5 mg/L from freshwater (0 ppt salinity) to salt water (~35 ppt salinity).

 

Air Calibration

The two methods described below may be used to achieve a 100% air-saturated environment:

Method 1:  Fill a clean beaker with distilled water. Bubble air through the water while stirring for 20 minutes. This will saturate the water with air.

Method 2:  Place a small amount of distilled water in the calibration bottle. Insert the electrode into the cap of the bottle. Place the cap on the calibration bottle loosely so that it remains vented to the atmosphere. Allow the electrode to sit in the calibration bottle for 20 minutes. The air in the bottle will be saturated with water.

Use either Method 1 or 2 to obtain a 100% air-saturated environment for the WQ-DO calibration.

To calibrate:

1.      Connect the dissolved oxygen probe to the PC via the USB connector.

2.      Let the dissolved oxygen probe warm up for 15-30 minutes before calibration. During the warm-up time, place the dissolved oxygen probe in a 100% air-saturated environment (Method 1 or 2 above).

3.      After the probe has warmed up for 15-30 minutes in a 100% air-saturated environment, click the Calibrate button and click on the DO Saturation reading.

4.      Enter the barometric pressure reading and click OK to calibrate.

 

wq do air calibration image

Figure 3: Click the Calibrate button

In-Situ Calibration

With a solution of a known dissolved oxygen concentration reading that has been verified with another calibrated meter or WQ-DO Sensor, it’s possible to calibrate per the mg/L:

1.      Connect the dissolved oxygen probe to the PC via the USB connector.

2.      Let the dissolved oxygen probe warm up for 15-30 minutes before calibration.  During the warm-up time, place the sensor into the known solution and allow the probe to stabilize.

3.     After the readings are stable, press the ‘Calibrate’ button and click the mg/L reading.

4.     Enter the known mg/L reading and click the ‘Calibrate’ button again.

 

Figure 4 Enter known mgL reading and click Calibrate again

Figure 4: Enter the known mg/L reading and click Calibrate again

If measuring dissolved oxygen in solutions that contain amounts of salinity such as salt water, make sure the salinity setting is changed in the Settings menu.

 

REV: 13H17

 

 

 

Leave a Reply

Your email address will not be published. Required fields are marked *

Time limit is exhausted. Please reload CAPTCHA.