When it comes to sensors and transducers, accuracy and resolution are two terms that are often a source of confusion so here is a helpful article to clear everything up. So here it is: accuracy vs. resolution…game on!
We will use a set of digital kitchen scales as the reference for our explanations:
- They have a rated capacity of 10kg (10,000 grams)
- They have a digital display that reads from 0.000kg to 10.000kg in steps of 0.001kg
- Their accuracy is better than ±0.1% of their rated capacity
Resolution
Resolution is the number of pieces or parts that the output or displayed reading from a sensor or measuring instrument can be broken down into without any instability in the signal or reading.
Resolutions can be expressed in a number of ways, the two most common being:
1. Decimal Places
Our 10kg kitchen scale has a resolution of kilograms to 3 decimal places or ‘3dp’. This expression is made relative to the engineering units in which the scale is set to read. Alternatively, if the kitchen scale was set to read from 0 grams to 10,000 grams in 1 gram increments it would be described as having a resolution of grams to zero decimal places.
2. Parts/Divisions/Counts
Our 10kg kitchen scale has a resolution of ‘1 part in 10,000’, ‘10,000 divisions’ or ‘10,000 ‘counts’. This expression describes resolution in absolute terms, rather than referring to an engineering unit.
Accuracy
Accuracy tells you how closely the output or displayed reading from a sensor or measuring instrument will match the ‘true’ value. Any mismatch between the reading and the ‘true’ value is usually referred to as the ‘error’.
In the case of our kitchen scale, this figure is <±0.1% of 10kg, which means that its reading will match the applied weight to ±0.010kg (±10 grams) or less, for instance:
- With exactly 4.000kg of weight applied to the scales the display reads 3.990kg. This is an error of 0.010kg or 0.1% of rated capacity.
- With exactly 5.000kg of weight applied to the scales, the display reads 5.004kg. This is an error of 0.004kg or 0.04% of rated capacity.
Practical Limitations
It is important to have the correct balance between accuracy and resolution to ensure that neither parameter is compromised. In our example we have an accuracy of 10 grams and a resolution of 1 gram, this is a good balance.
The resolution of 1 gram ensures that the accuracy of 10 grams can be resolved without creating a false impression of accuracy. For example, if the resolution was increased to 0.1 grams it tends to give users the impression that they have greater accuracy. This increased resolution can also cause undesirable display instability.
Want to know more? Read our other sensor reference articles.
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