The Different Techniques Used for Calibration Checks on Online Turbidity Meters

Calibration checks are a critical component of online turbidity meter maintenance to ensure accurate and reliable measurements. Turbidity meters are utilized in various industrial and municipal applications, including drinking water treatment, wastewater treatment, and chemical processing processes. As such, it is vital to periodically calibrate the instruments to confirm their accuracy and maintain compliance with regulations. This article will highlight the different techniques utilized for calibration checks on online turbidity meters.

Turbidity Meter Calibration

Turbidity meter calibration involves comparing the readings of the instrument to a reference standard of known turbidity value. The process aims to adjust the instrument reading to align with the reference standard to reduce measurement errors. Calibration should be carried out using regularly scheduled intervals, including after instrument repair, after prolonged use, and when expecting inaccurate readings.

Primary Standard Calibration Technique

The primary standard calibration technique compares the online turbidity meter's performance against a calibrated benchtop standard. The benchtop standard is a calibrated instrument of high accuracy and precision that has undergone meticulous calibration processes to achieve traceability to national standards. This technique follows guidelines outlined in ISO 7027, which outlines how to calibrate the online turbidity meter against the benchtop standard.

Process for Primary Standard Calibration

The process for primary standard calibration technique is simple. The benchtop standard is used to measure a sample of known turbidity, calibrated with a traceable national standard. The online turbidity meter then measures the same sample, and the difference between the readings is calculated. The instrument can then be adjusted to match the benchtop standard reading, ensuring the instrument is calibrated.

Secondary Standard Calibration Technique

The secondary standard calibration technique is a comparison of the online turbidity meter's performance against a secondary standard. The secondary standard is a less precise and accurate instrument than the primary standard, used to calibrate online turbidity meters. The secondary standard is not as sensitive as the primary standard, and its stability is monitored continually.

Process for Secondary Standard Calibration

The process of secondary standard calibration is similar to the primary standard calibration technique. The calibrated secondary standard instrument measures a known reference sample, and the turbidity meter measures the same sample. The difference in the readings between the secondary standard instrument and the turbidity meter is then recorded, and the instrument is adjusted accordingly to match the secondary standard reading.

Reagent Standard Calibration Technique

The reagent standard calibration technique involves the addition of a known quantity of turbidity reagent to a sample, which causes the sample to become cloudy. The instrument then measures the sample, and the reading is compared to the reference standard reading. This technique is ideal when calibration must be carried out over an extended period.

Process for Reagent Standard Calibration

The calibration process involves introducing the turbidity reagent to a water sample to induce turbidity. The calibrated instrument measures the turbidity level in the sample, and the online turbidity meter measures the same sample. The difference between the two readings is recorded, and the instrument is adjusted to match the benchmarked reading.

Regular Calibration Checks

Calibration checks should be conducted at regular intervals to ensure accurate measurements, and the frequency may vary depending on the application. Typically calibration checks should be carried out every 3-6 months; however, industries such as the food industry may require more frequent checks to maintain accuracy and compliance.

Conclusion

Calibration checks are crucial for maintaining accurate and reliable measurements on online turbidity meters. The calibration technique adopted will depend on the industry, the frequency of use, and the application. The primary and secondary standard calibration techniques are the most accurate, while the reagent standard calibration technique is suited to applications that require calibration over an extended period. Regular calibration checks are essential to maintaining instrument accuracy and compliance with industry standards.