ARDUINO PH 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 pH 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.

If this is your first-time calibrating the EZO pH circuit, we recommend that you calibrate in the following order:

Mid-point (pH 7) --> Low point (pH 4) --> High point (pH 10)

MATERIALS

Step 1: SINGLE, TWO POINT OR THREE POINT CALIBRATION

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

Two-point calibration will provide high accuracy between 7.00 and the second point calibrated against such as 4.00

Three-point calibration will provide high accuracy over the full pH range. Three-point calibration at 4.00, 7.00 and 10.00 should be considered the standard.

Note: The first calibration point must be the mid-point (pH 7)

Step 2: ASSEMBLE HARDWARE

The kit from Atlas includes 1 EZO pH circuit, 1 pH probe, 1 female BNC connector, 1 4oz pH4 calibration solution, 1 4oz pH7 calibration solution, 1 4oz pH10 calibration solution,1 4oz pH storage solution, 1 optional inline voltage isolator.

Ensure that the pH 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 pH 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_pH_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.

c) 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 4: MID-POINT CALIBRATION

a) Remove the soaker bottle and rinse off the pH probe.

b) Pour some of the pH 7.00 calibration solutions into a cup. Ensure that there is enough solution to cover the sensing area of the probe.

c) Place the pH probe into the cup and stir it around to remove trapped air. Let the probe sit in the calibration solution until the readings stabilize (small movement from one reading to the next is normal).

d) Wait for the readings to stabilize (1-2 minutes). Once stabilized issue the mid-point calibration command cal,mid,7

Step 5: LOW-PONT CALIBRATION

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

b) Pour some of the pH 4.00 calibration solutions into a cup. Ensure that there is enough solution to cover the sensing area of the probe.

c) Place the pH probe into the cup and stir it around to remove trapped air. Let the probe sit in the calibration solution until the readings stabilize (small movement from one reading to the next is normal).

d) Wait for the readings to stabilize (1-2 minutes). Once stabilized issue the low-point calibration command cal,low,4

Step 6: HIGH-POINT CALIBRATION

a) Rinse off the probe before calibrating to the highpoint.

b) Pour some of the pH 10.00 calibration solutions into a cup. Ensure that there is enough solution to cover the sensing area of the probe.

c) Place the pH probe into the cup and stir it around to remove trapped air. Let the probe sit in the calibration solution until the readings stabilize (small movement from one reading to the next is normal).

d) Wait for the readings to stabilize (1-2 minutes). Once stabilized issue the high-point calibration command cal,high,10

Step 7: ADDITIONAL INFORMATION

  • Issuing the cal,mid command after the EZO pH circuit has been calibrated, will clear the other calibration points. Full calibration will have to be redone.
  • The EZO pH circuits default temperature compensation is set to 25°C. If the temperature of the calibration solution is +/- 2 °, consider setting the temperature compensation first. Temperature changes of < 2° C are insignificant.

Share

    Recommendations

    • Stone Concrete and Cement Contest

      Stone Concrete and Cement Contest
    • Games Contest

      Games Contest
    • Sew Tough Challenge

      Sew Tough Challenge

    Discussions