Introduction: Atlas Scientific EZO PH 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.

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

The Atlas EZO pH circuit has a flexible calibration protocol, allowing for single-point, two-point or three-point calibration. If this is the first-time calibrating the EZO pH circuit, it is recommended that you calibrate in the following order:

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

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.

Doing a mid-point calibration after the pH circuit has been calibrated will clear the other calibration points. Hence the mid-point must be done first.

Step 1: Mid-Point Calibration

a) Enable continuous readings.

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

c) Remove the top to the ph 7 calibration solution pouch. Place the pH probe inside 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).

e) Once the readings have stabilized, issue the mid-point calibration command cal,mid,7

Step 2: Low-Point Calibration

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

b) Open the pouch of pH 4 calibration solution, and place the probe inside the pouch.

c) Wait for the readings to stabilize (1-2 minutes)

d) Once the readings have stabilized issue the low-point calibration command cal,low,4

Step 3: High-Point Calibration

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

b) Open the pouch of pH 10 calibration solution, and place the probe inside the pouch.

c) Wait for the readings to stabilize (1-2 minutes)

d) Once the readings have stabilized issue the low-point calibration command cal,low,10