Last week we featured a “How to” video on smart antenna installations and here you can find other “How to” videos we done throughout the years.
An Emerson colleague, Charu Pandey, alerted me to one published this week. In the video, How to Calibrate pH Sensors with Two Buffer Solutions | Emerson (run-time 4:01), Charu demonstrates this calibration process. It’s recommended that before you begin, you have the Rosemount pH/ORP Sensors Quick Start Guide on hand. This is where you will find all the necessary instructions and best practices for installation and calibration.
Visit the Liquid Analysis section on Emerson.com for more information on the complete range of analytical sensors and instruments to help you more efficiently manage your process liquids and equipment.
Hi, my name is Charu Pandey and I am a Product Specialist for Liquid Analysis at Emerson. In this video, I will be walking you through how to calibrate a pH sensor with two buffer solutions.
Before you begin, be sure to have on hand the Rosemount pH/ORP Sensors Quick Start Guide, which can be found on the Emerson website. This is where you will find all the necessary instructions and best practices for installation and calibration.
A two-point buffer calibration is the best way to ensure that a pH sensor is providing accurate measurements. Sensors should be calibrated after start-up and if there is a drift in the measurement. During a two-point calibration, the transmitter calculates new values for slope, millivolts, over pH, and offset in millivolts. These values are based on the millivolt response of the sensor when it is submerged in the pH buffer solutions.
There are two ways to perform a pH calibration, Auto and Manual. Today, we will be going through the Auto calibration. First, ensure that the pH sensor is clean by rinsing the sensor with tap water to remove any process liquid and debris To access the auto calibration, first press the ‘Enter/MENU’ button on the transmitter, then select ‘Calibrate’. Next, select the Sensor you are calibrating. And in this case, “S1 Measurement”. Then press the down arrow and select ‘Auto buffer’, hit ‘Enter’. And finally, “Start Calibration.”
Now you can follow the directions on the transmitter screen. Place the sensor in the first buffer solution, and press ‘Enter’ on the transmitter. Wait for the readings to stabilize. The transmitter will display a list of possible buffer solutions. Select the option that matches the label on the bottle.
Now remove the sensor from the first buffer solution and rinse with tap water. Next, repeat these steps with the second solution. Place the sensor in the second buffer, and press ‘Enter’. Wait for the readings to stabilize. Then select the solution that matches the value shown on the bottle and press ‘Enter’.
After this calibration sequence is complete, the transmitter will display a slope and offset. Look at the slope to determine if the sensor needs to be replaced. An acceptable slope for a pH sensor is between 50 and 59.16. Ideally, a healthy pH sensor will have a slope between 57 and 59.16.
The acceptable offset for a healthy pH sensor is between negative 60 and 60 millivolts. Ideally, a pH sensor will have an offset as close to 0 millivolts as possible. The transmitter will return to normal functioning after you select X or Exit. Now, rinse the sensor a final time and place it back into the process.
This completes the overview of how to auto-calibrate a pH sensor with two buffer solutions.
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