Is the signal drifting or inaccurate?
1. Accumulated debris on the sensing element (tip of the electrode) may be the cause. Perform a visual inspection on the tip and follow the steps provided in the table below for cleaning depending on what type of debris may be building up on the electrode. Even if there are no visible signs of build-up, a general cleaning in 0.1M HCl is recommended to be done consistently. Recalibrate the electrode and pay attention to how long the output takes to stabilize (Stabilization is defined as less than 0.01mA change per minute). Slow stabilization may mean that the electrode reference solution is diluted.
2. Dilution occurs whenever the solution being measured differs from the reference solution and some solutions cause faster dilution. Dilution will result in drift at an increasing rate over the life of the electrode. To check this, calculate the slope error and offset of the electrode after cleaning and calibrating. If unsure how to calculate these, please reference our Sensor Calibration article. Values outside of accepted ranges indicate that the reference electrolyte is diluted or dirty. The further out of range these values are, the greater the drift rate will be.
Some electrodes are refillable and will allow the reference to be replaced by the user, while others are replaceable and will require purchase of a new electrode. pHionics currently has replaceable electrodes because they provide the lowest maintenance time and fewer complications.
3. Slight and extreme inaccuracies can result from nearby sources of interference such as pumps, boats, or radio frequencies. The pHionics STs Series provides excellent noise reduction to prevent interference but sensors and transmitters from other manufacturers may not ever function properly in environments with high levels of background noise.
For a more in-depth guide, check out our new pH Drift Troubleshooting Guide.