Learn how to do an offline calibration for a Memosens pH sensor with auto-calibration on the Protos 4400 transmitter.

Offline pH Calibration

We will perform this calibration offline in a controlled environment right here in our workshop. Since our connected sensor is a Memosens smart digital sensor, it will store the calibration in the head of the sensor. When performing a calibration in the field, you can follow these same steps.

Calibration Menu

Let’s begin by pressing Menu on the main screen and then enter on the calibration menu. If access the calibration menu requires a passcode, please note that the default passcode is 1147. Once within the calibration menu, we’ll select the Memosens pH sensor connected to channel 1 of our transmitter.

I will be conducting a Calimatic or automatic calibration today, but here you can see the different options available for calibrating. The Protos enables us to perform a manual calibration, a product calibration, or a single point standardization, adjustment of the electrode slope and zero-point via data entry, and lastly adjustment of the internal temperature detector. Make sure you select Calimatic here before proceeding further. Under the number of calibration points, we will select 2-point and then move on to select the buffer set.

Buffer Set

Since we are using automatic calibration, it’s very important to select the proper buffer set  in your Protos transmitter. This ensures automatic recognition of the buffer’s value as well as automatic temperature compensation during the calibration process. The Protos has numerous buffer tables stored within its software for selection by the operator. It’s important to note that Nist technical is most commonly used. Verify your buffer values by cross-checking the labels against the values on the bottom of the screen. We will select the Knick CaliMat buffers and press enter to continue.

Beginning Calibration

Once we are ready to perform our calibration process, we will select the Next button and move to the first steps. As you can see, once the calibration process begins, the transmitter enters a hold mode — holding the output to the control system. The NAMUR wrench icon in the top left corner of our display indicates this as well.

First Buffer

Here, we get a prompt to rinse the sensor with DI water and immerse it in the first buffer solution. We will do so and place the sensor into the buffer 7. Please be sure to immerse the entire pH measuring bulb along with the sensor’s junction in the buffer. Stir lightly and then press the Next button. After pressing Next, the transmitter will begin to check the drift of the sensor in the first buffer solution. You can see that the transmitter automatically recognizes the buffer value. The raw pH voltage value is displayed along with the measured temperature and response time of the electrode in the buffer.

Second Buffer

Once finished in the first buffer solution, the transmitter will prompt you to once again rinse the sensor and immerse it in the second buffer solution. We will do so and then place our sensor in the buffer 4 solution. Again, stir lightly and then press Next to proceed to the next step. As with the first step, you can see that the transmitter automatically recognizes the buffer value and displays the pH voltage, temperature, and response time.

Calibration Record

Once complete in the second buffer, our Protos displays the specifics of your calibration record. Here you can see we have a timestamp of our calibration followed by the calibration mode and the specific values of the zero point and slope of the electrode. The Sensoface icon in the top left corner of our display indicates the status of our calibration. We have our zero-point displayed as a pH value, followed by the slope displayed as millivolts per pH, and finally a smiley face indicating a successful calibration.

Finalizing

Lastly, you can see that we have the ability to select calibrate or adjust. It’s important to note that no adjustments are made to the sensor without selecting the Adjust button. Selecting Calibrate allows us to restart the process. We will select the adjust button to finalize the process. We are now ready to go online with our measurement or disconnect our calibrated sensor for future use in the field.

Be sure to check out our other videos on the Protos 4400 transmitter by Knick.