pH/ORP Frequently Asked Questions

Flow rate does not directly affect pH itself, but it can influence pH measurement accuracy. Flow rate affects the boundary layer around the sensor, potentially altering response times and measurement stability. For most applications, flow rate has minimal impact on pH measurement, typically causing only small variations in the order of ±0.1 pH. In high-purity water, however, flow rate strongly affects measurements; therefore, it is recommended to place sensors in flow chambers with low flow rates to ensure accurate readings. 

Calibration frequency depends on various factors, including process conditions and sensor performance requirements. Calibration intervals can vary from once a day to once a month, but starting with more frequent calibrations and extending the interval based on stability and accuracy is a good practice. The frequency of calibration can be optimized based on sensor feedback. Our ISM™ technology features predictive diagnostic tools including an Adaptive Calibration Timer. This optimizes calibration intervals by monitoring a sensor's condition and predicting the number of days remaining until the next calibration should be performed. ISM’s predictive diagnostics analyze sensor performance trends, allowing calibration schedules to be precisely tailored to each sensor’s needs. This not only ensures measurement accuracy but also maximizes sensor utility, reducing unnecessary maintenance. 

Sensor drift in ORP (redox) readings can indicate a need for recalibration or highlight issues with the sensor itself. Through ISM’s diagnostic capabilities, users can quickly determine the cause of drift, whether it be sensor aging or external factors affecting the measurement. This insight facilitates timely corrective actions, ensuring reliable ORP monitoring. ORP drift can also result from changes in process composition, pH fluctuations, or sensor aging. ORP readings stabilize in well-defined oxidizing or reducing conditions. Measurement drift in pure water relates to dissolved oxygen or contaminants in the water. If drift is observed, it is advisable to check the sensor for any signs of aging or damage and consider recalibration or replacement as necessary.

Yes, we recommend that ORP sensors are calibrated and we sell the respective ORP buffer solutions. Our ORP calibration standards allow for accurate sensor calibration, ensuring reliable measurement performance. These standards are designed for easy use and help maintain the precision and accuracy of your ORP readings under various industrial conditions. We provide a comprehensive range of ORP calibration standards to suit diverse application requirements. These standards and our ISM technology ensure that sensors are calibrated for optimum performance, integrating seamlessly into your process management system. 

The lifespan of pH and ORP sensors varies widely, ranging from weeks to years, depending on application conditions such as temperature, pressure, and sample media. Regular calibration and proper maintenance can extend sensor life. Selecting a sensor with a glass membrane and reference system suitable for your specific application can also significantly enhance its operational lifespan. ISM technology enhances sensor longevity by continuously monitoring sensor “health” and providing predictive diagnostics. These diagnostics tell operators when sensor maintenance or replacement will be required. This proactive approach to sensor management extends operational life and maintains high measurement accuracy.

When stored properly at room temperature, dry, and in original packaging, sensors can last well over a year without performance degradation. To ensure the longest possible shelf life, it is critical to store sensors with their original storage (watering) cap and solution in place and to avoid exposure to conditions where the storage solution could dry out or leak. Optimal storage conditions are critical for preserving sensor functionality over time. 

Regular cleaning, as per the manufacturer's instructions, may be essential to maintain accuracy and extend a probe's lifespan. The frequency of cleaning should be adjusted based on the level of contamination and type of process. More frequent cleaning will be required for heavily contaminated process media to ensure consistent and accurate pH readings. By adhering to the necessary cleaning regime, users can maintain optimal sensor performance and prolong probe life. Cleaning and calibration can be fully automated with a METTLER TOLEDO EasyClean system.

Rejuvenation methods vary by probe type and condition. pH sensors can be soaked in a cleaning solution recommended by the manufacturer. This can help to remove buildup and restore response time. A calibration is recommended after cleaning to ensure optimal measurement performance. ISM Core software guides the operator in cleaning and calibrating the sensor for optimal results. If a probe's performance does not improve after cleaning, consulting the manufacturer's guidelines for further rejuvenation steps or considering probe replacement may be necessary.