This is one of our frequently asked questions, one of our service engineers has answered it below.
There are no set guidelines for the frequency of calibration. Often the probes are routinely recalibrated every 3, 6 or 12 months depending on operator. The drift is usually found to be minimal but calibration does serve to provide a functional check on the probe. Alternatively water samples could be routinely sent for laboratory analysis to ensure the probe is still reading accurately.
When measuring suspended solids, if there could be changes in the particle types over time then regular recalibration will be necessary. For example if seasonal changes in particles can be expected or in a quarry the material could change as the quarry expands. Again there are no set guidelines for calibration and this is for the user to assess. Usually a 3, 6 or 12 month interval will suffice.
These can easily be periodically checked. Remove the sensor from the water, clean it and allow it to dry off. Place out of any wind and allow the sensor to acclimatise to the air temperature for about 30mins. The sensor should read approx 100% saturation in air. If it is not close to 100% then it may require re-calibration. It may also be worth considering replacing the electrolyte and membrane which should be done annually as standard.
Check that it reads 100% in air as above. The cap will need replacing every two years but a warning should appear on the 7300 monitor screen to notify the user.
These can be checked by cleaning in clean water, drying in air and placing the sensor in pH 4, 7 & 10 standards (ensuring the small metal temperature sensor is submerged). The electrode will degrade over time so these probes should be calibrated and checked every 6 months. As part of a planned servicing routine we would suggest also replacing the electrode every 6 months.