ARDUINO SALINITY 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 salinity/conductivity K1.0 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.

MATERIALS

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Step 1: SINGLE POINT OR TWO POINT CALIBRATION

The Atlas EZO conductivity circuit has a flexible calibration protocol, allowing for single-point or two-point calibration.

Single point calibration will provide a narrow range of accuracy.

Two-point calibration will provide a wide range of accuracy.

Step 2: ASSEMBLE HARDWARE

The kit includes 1 EZO EC circuit, 1 K1.0 conductivity probe, 1 female BNC connector, 4oz calibration solutions :12880µS and 80000µS,1 optional inline voltage isolator.

Ensure that the conductivity 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 conductivity circuit to the Arduino Uno as shown in the schematic above and connect the probe to the BNC connector.

Step 3: LOAD PROGRAM ONTO ARDUINO UNO

a) Download the sample code from this LINK. It will be in a folder titled "arduino_UNO_EC_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 conductivity circuit. As a test, enter the command iwhich will return the device information.

Step 4: ENABLE CONTINOUS READING AND SET PROBE TYPE

a) Ensure that the probe's cap is removed and that it is dry. With the probe in air, send the command c,1 which will enable continuous readings once per second.

b) If your probe is not K1.0 (default), then set the probe type using the command k,n

Where n is the k value of your probe. In this tutorial, we will be using a K1.0 probe. The probe type can be confirmed with command k,?

Step 5: DRY CALIBRATION

Send the command cal,dry

Even though you may see readings of 0.00 before issuing the command, it is still necessary to do a dry calibration.

Step 6: TWO POINT CALIBRATION - Low Point

a) Pour some of the 12880µS calibration solution into a cup. Ensure that there is enough solution to cover the sensing area of the probe.

b) Place the probe into the cup and stir it around to remove trapped air. Let the probe sit in the solution. Readings maybe off by +/- 40% from the stated value of the calibration solution.

c) Wait for readings to stabilize (small movement from one reading to the next is normal) and send the command cal,low,12880

Note: The readings will not change after this command is entered.

Step 7: TWO POINT CALIBRATION - High Point

a) Rinse off the probe before calibrating to the high point.

b) Pour some of the 80000µS calibration solution into a cup. Ensure that there is enough solution to cover the sensing area of the probe.

c) Place the probe into the cup and stir it around to remove trapped air. Let the probe sit in the solution. Readings maybe off by +/- 40% from the stated value of the calibration solution.

d) Wait for readings to stabilize (small movement from one reading to the next is normal) and send the command cal,high,80000

Note: The readings will change after this command is entered. Calibration is now complete.

Step 8: SINGLE POINT CALIBRATION

a) Pour some calibration solution into a cup (μS value of your choice). Ensure that there is enough solution to cover the sensing area of the probe.

b) Place the probe into the cup and stir it around to remove trapped air. Let the probe sit in the solution. Readings maybe off by +/- 40% from the stated value of the calibration solution.

c) Wait for readings to stabilize (small movement from one reading to the next is normal) and send the command cal,n where n is the value of the calibration solution.

Note: Readings will change after the command is entered. Calibration is now complete.

Step 9: TEMPERATURE COMPENSATION DURING CALIBRATION

Temperature has a significant effect on conductivity/salinity readings. The EZO conductivity circuit has its temperature set to 25 ̊ C as the default.

At no point should you change the default temperature compensation during calibration.

If the calibration solution is +/- 5 ̊ C (or more), refer to the chart on the bottle and calibrate to the corresponding value.

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