There is definite set of instructions suitable for calibrating oxygen sensors. The best practices also vary between device types and different manufacturers. Despite this diversity, all methods of oxygen sensor calibration typically adhere to the same set of underlying principles. Essentially, the sensor is exposed to a calibration standard of known value and the reading is adjusted accordingly to achieve an ideal response.
When oxygen sensors are first purchased, they come factory calibrated. However, to ensure the best possible response in critical applications and to correct drift over time, it is important to calibrate the sensor within its end-use system. This means running standardised calibration tests periodically to maintain the sensor’s precision and resolution, thus maintaining its accuracy by guaranteeing highly repeatable measurements at your desired resolution.
The method of calibration used depends on various interconnected factors, this includes the number of relevant measurement parameters. For example: Dissolved oxygen sensors are often subject to one-point calibration in 100% air-saturated water which demands careful control/understanding of three key variables: barometric pressure, salinity, and temperature. Below are some of the best practices for single-point dissolved oxygen sensor calibration:
One-point oxygen sensor calibration is useful when it comes to saving money, as it is easy to create the right measurement environment. However, your application may demand accuracy at more than a single measurement level, which means one-point calibration will be insufficient. Two-point oxygen sensor calibration is slightly more complex as it uses two data points: A zero reference and a span. It is important to eliminate residual air bubbles from the liquid standard when trying to acquire a zero reference and ensure the temperature is consistent.
Oxygen sensors that do not have a linear response across the measurement range could require some measure of algorithmic curve-fitting. This is so it can match the actual response as closely as possible to the ideal response across the full measurement range. Most commercially available oxygen sensors have characteristic curves with well-understood deviations from the ideal reading.
Most oxygen sensor calibration standards will have 5-points or less, which means users will often have a few reference clusters relating to key parameters. This means you may have to carry out the bespoke characterisation of your sensor in situ to derive the correct linearization formula.
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