Introduction: Atlas Scientific EZO DO Calibration Procedure

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 wide…

This tutorial describes the calibration procedure. It is assumed that the user has their hardware and code working and is now ready to calibrate the sensor.


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. For instructions on how to change between protocols refer to: How to change data protocol of Atlas sensors

The Atlas EZO DO (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. As such calibrate first, compensate later.

Step 1: Single Point Calibration

a) Enable continuous readings

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

c) Once the readings have stabilized issue the calibration command cal

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

Step 2: Dual Point Calibration (optional)

Only perform this calibration if you require accurate readings below 1.0 mg/L.

a) After you have calibrated the EZO DO circuit using the cal command; remove the top of the zero dissolved oxygen calibration solution pouch, insert the probe, and stir it around to remove any trapped air (which could cause readings to go high). Let the probe sit in the zero D.O calibration solution until the readings stabilize. (small movement from one reading to the next is normal)

b) Once the readings have stabilized, issue the calibration command cal,0