Why do we need to calibrate sensors?
There are a lot of good sensors these days and many are ‘good enough’ out of the box for many non-critical applications. But in order to achieve the best possible accuracy, a sensor should be calibrated in the system where it will be used. This is because:
- No sensor is perfect.
- Sample to sample manufacturing variations mean that even two sensors from the same manufacturer production run may yield slightly different readings.
- Differences in sensor design mean two different sensors may respond differently in similar conditions. This is especially true of ‘indirect’ sensors that calculate a measurement based on one or more actual measurements of some different, but related parameter.
- Sensors subject to heat, cold, shock, humidity etc. during storage, shipment and/or assembly may show a change in response.
- Some sensor technologies ‘age’ and their response will naturally change over time – requiring periodic re-calibration.
- The Sensor is only one component in the measurement system. For example:
- With analog sensors, your ADC is part of the measurement system and subject to variability as well.
- Temperature measurements are subject to thermal gradients between the sensor and the measurement point.
- Light and color sensors can be affected by spectral distribution, ambient light, specular reflections and other optical phenomena.
- Inertial sensors are sensitive to alignment with the system being measured
What makes a good sensor?
The two most important characteristic of a sensor are:
- Precision – The ideal sensor will always produce the same output for the same input.
- Resolution – A good sensor will be able to reliably detect small changes in the measured parameter.