TI Precision Labs: Sensor accuracy error and repeatability

20th August 2019
Lanna Cooper

In this video, Texas Instruments will discuss the meaning of accuracy and error in the context of temperature sensors and go through examples to explain how these terms are used to characterise a system's performance. Finally, we'll discuss repeatability and how this could affect the system's overall accuracy.

One of the most important characteristics of a sensor is its accuracy, because the accuracy affects the overall temperature measurement in the system. Different air sources cause the accuracy of a sensor to be affected.

In other words, for a system to have very high accuracy, it must have very low error. These two terms may be interchangeably used when specking a temperature sensor.

As an example, the three thermometers shown are used to measure the temperature of the same source. Two of these thermometers read the same value, while the third reads a different value. So the natural question here is, which one is the accurate reading?

Just because two thermometers, as shown in the example, read the same temperature does not necessarily make its reading accurate. We will come back to answering this question once we understand what accuracy and repeatability are. To better understand accuracy and error, let's take a look at some of the ways an error may be defined for a temperature sensor.

Error may be defined as a percentage of the measurement, a percentage of the full scale, or as an absolute value. Extreme care must be taken when interpreting the error of a lower value of relative terms may mean a higher absolute error.

As an example, let's take two temperature sensors which have a temperature span of 0°C to 120°C.

One temperature sensor is specified with an error of one percent of the measurement at 25°C, while another is specified with an error at 0.5% of the full scale. When converted to absolute error value, one percent of the measurement gives an error at 0.25°C, while 0.5% of the full scale makes the error 0.6°C.

Clearly, a lower value in percentage may not be a lower value in absolute terms. In the datasheet for temperature sensors, the sensor is most commonly specked as an absolute value. This makes it simpler to compare temperature sensors when accuracy is critical to the application.

In the electrical characteristics of a digital temperature sensor datasheet, the accuracy is often specified in a table as shown. This is also reflected in the temperature accuracy graph. As can be seen, the accuracy of the temperature sensor is specified over a specific temperature range.

For example, in the full temperature range from negative 55°C to 150°C, the typical temperature error will be plus or minus 0.1°C. The typical values may be based on measurements done on specific parts.

For more information, watch the video below.

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