Introduction: Atlas Scientific EZO ORP 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 ORP (oxidation-reduction potential) circuit has a flexible calibration protocol, allowing single point calibration to any off the shelf calibration solution. However, if this is your first time calibrating the EZO ORP circuit, Atlas Scientific recommends using the 225mV calibration solution.

Step 1: Single Point Calibration

a) Enable continuous readings.

b) Remove the soaker bottle and rinse off the ORP probe.

c) Remove the top of the ORP 225mV calibration solution pouch. Insert the ORP probe directly into the pouch, and let the probe sit in the calibration solution until the readings stabilize (small movement from one reading to the next is normal).

d) Once the readings have stabilized send the command cal,225

Calibration should be done at least once per year. If the ORP that is being read is continuously on the extremes of the scale ( ~ -900mV or +900mV) calibration may have to be done more often. The exact frequency of calibration will have to be determined by your engineering team.