Here is an extract from the DrDAQ help files:
Calibrating for accurate pH measurements
Calibration is only required when accurate (better than 0.5pH)
measurements are required. Calibration should be performed just before the measurements are made. User calibration information is stored separately in PicoScope and PicoLog, so if you wish to measure pH accurately with both programs, 2 calibrations will be required.
To calibrate a pH electrode you will require at least 2 pH buffers (pH4, pH7 and pH10 buffers are widely available). Calibration should be performed with the ambient temperature close to 25Â°C.
A container of clean water is also required to wash the electrode before moving it from one buffer to another.
1. Connect the pH electrode to DrDAQ and display pH using either PicoScope or PicoLog (depending on which program you are calibrating for).
2. Place the electrode in the first solution and wait for at least 30 seconds for the readings to stabilise (gently stirring helps).
3. Make a note of the reading and repeat the procedure for each of the buffer solutions (do not forget to wash the probe clean before swapping from one buffer to another.
4. You should now have a table of readings similar to the one below:
pH Buffer value at 25Â°C Measured value from DrDAQ
pH calibration with PicoLog
As already mentioned you will need to note down the measured pH value and compare it with the actual value to create a lookup table. Then follow the steps below:
1. Got to 'Settings' and click on 'Input Channels' on the pull down menu.
2. The converter input type will then be displayed, check settings and click 'OK'. You should now see the DrDAQ measurements box.
3. Select pH and click 'Edit'.
4. Click 'Options' from the Edit measurement box.
5. Now click on 'Scaling' and select 'Look up table' from the menu box.
6. Enter the real measured pH value below Raw and the actual value in 'Scaled' (similar to the table in the previous section)
7. Click 'OK' for all open boxes and verify the calibrated pH readings.
I hope this helps.
Michael - Tech Support
Web Support Forum