ARDUINO DISSOLVED OXYGEN SENSOR CALIBRATION

About: Founded in 2005, Atlas Scientific specializes in building laboratory grade sensing equipment for robots, appliances, and industrial control systems. Thousands of Atlas Scientific sensors can be found in a wi...

In this tutorial, we will be calibrating Atlas Scientific's EZO dissolved oxygen (D.O) sensor using Arduino Uno.

CALIBRATION THEORY

The most important part of calibration is watching the readings during the calibration process. It is easiest to calibrate the device in its default state (UART mode, with continuous readings enabled). Switching the device to I2C mode after calibration will not affect the stored calibration. If the device must be calibrated in I2C mode be sure to continuously request readings so you can see the output from the probe. In this tutorial, the calibration will be done in UART mode.

The Atlas dissolved oxygen circuit has a flexible calibration protocol, allowing for single point or dual point (optional) calibration. Temperature, salinity and pressure compensation values have no effect on calibration. Do the calibration first and compensate for these parameters later.

MATERIALS

Step 1: ASSEMBLE HARDWARE

The kit from Atlas includes 1 EZO D.O circuit, 1 D.O probe, 1 female BNC connector, 1 4oz calibration solution,1 optional inline voltage isolator.

Ensure that the D.O circuit is in UART mode. For instructions on switching between protocols, refer to the following LINK.

Use the breadboard to mount the circuit and BNC connector. Wire the D.O circuit to the Arduino Uno as shown in the schematic above and connect the probe to the BNC connector.

Step 2: LOAD PROGRAM ONTO ARDUINO UNO

a) Download the sample code from this LINK. It will be in a folder titled "arduino_UNO_DO_sample_code".

b) Connect the Arduino to your computer.

c) Open the code downloaded from step a, in your Arduino IDE. If you do not have the IDE you can download it from HERE.

d) Compile and upload the code to Arduino.

e) Open the serial monitor. For access go to Tools -> Serial Monitor or press Ctrl+Shift+M on your keyboard. Set the baud rate to 9600 and select "Carriage return". You should now be able to communicate with the D.O sensor. As a test, enter the command i which will return the device information.

Step 3: SINGLE POINT CALIBRATION

a) Carefully pull off and discard the cap from the D.O probe.

b) Let the probe sit, exposed to air until the readings stabilize. Note: Small movement from one reading to the next is normal.

c) Once the readings have stabilized issue the calibration command calin the serial monitor.

After calibration is complete, you should see readings between 9.09 - 9.1x mg/L, only if temperature, salinity and pressure compensation are at the default values.

default temperature = 20°C, default salinity = 0, default pressure = 101.3kPa

Step 4: DUAL POINT CALIBRATION

Note: Only perform this calibration if you require accurate readings below 1 mg/L.

a) After you have calibrated the D.O circuit using the "cal" command; place the probe into the calibration solution. Stir the probe around to remove trapped air (which could cause readings to go high).

b) Let the probe sit in the calibration solution until the readings stabilize. Note: Small movement from one reading to the next is normal.

c) Once the readings have stabilized issue the calibration command cal,0 in the serial monitor.

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