1114 - Wireless O2 Dissolved Sensor

The diagram below shows the specific parts of the sensor. Read further to explore the functionality of each part of the sensor.

The dissolved oxygen sensor has two component parts:the wireless sensor body and the electrode.

1. Sensor End Cap
2. Status Indicator
3. On/Off Switch
4. USB Port
5. Unique ID Number

Sensor End Cap (1)

Most Smart Wireless Sensors feature an end cap that is specific to the requirements of the device's internal sensor. The sensor's end cap is the direct interface between the device’s internal sensor and your experiment.

The Status Indicators (2)

The sensor features a single status indicator that changes colour and flashes. See the table below for further information.

On/Off Switch (3)

The sensor's on/off switch allows you to turn the sensor on, off or perform a hard reset.

To switch the sensor off

• Press and hold down the On/Off switch until the white light shows, then release.
• If not communicating with the EasySense2 app, the sensor will turn off after a period of one hour of inactivity. 

Hard resetting the sensor

• If necessary, attach the sensor to power.
• Press and hold down the On/Off button for at least 8 seconds until the status LED gives a flash of blue light, then release.
• If the sensor fails to respond, contact Product Support at Data Harvest. Please provide details of:  
• The computer platform it is being used with and the EasySense2 app’s version number.
• A description of the problem being encountered. 

USB Port (4)

Use to connect to a computer or a charging unit.

For specific USB or Bluetooth connectivity instructions, please see the 'Connectivity' section of this documentation. 

For instructions on charging your device, see the section on 'Charging the Sensor'. 

Unique ID Number (5)

All Smart Wireless Sensors are labelled with a unique ID number. This number is used in the EasySense2 app, so that you can identify each sensor when making a connection wirelessly.

The Electrode

The electrode is an epoxy bodied probe with an electrode at one end. The electrode that makes the electrochemical cell is a silver anode (the long section) and a gold cathode (the end point electrode).

A membrane cap goes over the electrode. When correctly in place, the membrane presses down (lightly) on the gold cathode and electrically isolates it from the silver anode. The membrane cap is filled with an electrolyte solution. The electrolyte solution for this electrode is KCl; it is not advised that NaCl based electrolyte is used as an alternative.

The electrolyte will have absorbed oxygen during storage (more so if the bottle is becoming depleted). This dissolved oxygen in the electrolyte will have to be scavenged out before readings will have any accuracy.

When filling the membrane cap, ensure that no air bubbles are trapped in the cap. If the cap is slightly overfilled to create a positive meniscus, then as you tighten the membrane onto the electrode body, excess electrolyte will escape via the screw thread, therefore take time attaching the cap to let any excess fluid escape.

Preparing the electrode for use.

• Place the membrane cap, with the membrane downward, on a clean surface. 
• Half fill the cap with the electrolyte supplied. Tap the cap gently to remove any air bubbles from the electrolyte. 

Note: It is important to remove trapped air bubbles because they will feed oxygen to the cathode and hence cause extra signal current to flow regardless of the oxygen concentration in the sample.

• Hold the electrode body vertically (with the cable uppermost) and screw on the membrane cap. One side of the thread is flat which will allow any surplus electrolyte to escape. Unscrew slightly to release any pressure and then gently screw the cap on until it is just tight. 

Note: Do not over tighten – the membrane should not be pressurised (bulging away from the cathode tip), as it will become thin and oversensitive.

The assembled electrode must stay connected to an awake sensor unit to keep it polarised. If disconnected, reconnect for 10 minutes before use.  

Before use go to Devices and select the appropriate range.

There is a choice of:

• 0 – 150 %Sat 
• 0 – 250% Sat
• 0 – 15 mg/L
• 0 -20 mg/L

Unless the sensor is being used for comparative work it will need calibrating before use.

To calibrate for use in an Aqueous solution e.g. water 

1. The range of the Sensor should be set to measure oxygen in water, 0 – 150 (%Sat).
2. After the electrode has been polarised for at least 30 minutes, hold the electrode vertically 10 mm above a sample of stirred distilled water (so the air is saturated with water vapour) for about 60 seconds. Do not let the membrane get wet. 
3. Select Devices > Calibrate
4. Follow the instructions.

Using the mg/L range

You will need to supply a value for air pressure and the temperature of the aqueous solution. These functions assume the temperature and pressure are constant and that the effect of dissolved solutes is negligible e.g. water. 1mg/L = 1 ppm.