4 electrode conductivity sensors are unique due to their open geometry and ability to accurately measure conductivity over a large range. There are some basic installation tips that should be followed to the best accuracy when using these products.
Conducell 4 UxF Products
These sensors have the electrodes flush at the tip of the sensor. The electrodes generate a small electrical field that passes through the liquid. The field can be skewed by the piping or vessel thus causing an offset in the measurement. Hamilton recommends at least 10mm of spacing from the tip of the sensor and a minimum 30mm diameter around the tip to avoid this issue.
The Conducell 4US uses exposed electrodes through the length of the body. The electrical field is most prominent on to the sides of the sensor. Hamilton recommends a minimum 60mm diameter to prevent errors.
These same rules should be followed during the calibration process. When the sensor is immersed in a liquid calibration standard care should be taken to avoid any interference from the walls of the beaker used for calibration.
Non-conductive gas bubbles on the electrode are another source of error. During calibration, visually inspect the sensor to see if any bubbles have formed on the electrode surface. If so, try tapping the sensor against the beaker to remove them. In process installations avoid installing the sensor directly over sparger nozzles. Try to mount the sensor so that the tip has good flow passing perpendicular to the electrodes. This tangential flow helps to sweep away bubbles so they cannot collect on the electrode surface.