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Standard Error Measurement vs Maximum Measurement deviation: Understanding the different methods of specification when it comes to pressure sensor applications.

It is incredibly important to interpret the specifications of a pressure sensor correctly. In an unregulated market, it pays to understand the difference between the standard error of measurement and the maximum measurement deviation. You also be able to define how they impact the performance of your pressure sensor applications.

Leading sensor and measurement device specialists, Baumer provide excellent pressure sensors that are accurately specified, guaranteeing reliable applications for their customers. In this article, Process Industry Forum look at how to effectively interpret specifications to deliver reliable pressure sensor applications.

Maximum measurement deviation vs isolated standard error of measurement

There are two fundamentally different methods of specification when it comes to sensors. Maximum measurement deviation and the standard error of measurement. Before looking at these methods, it is important to understand the difference between precision and accuracy for measuring sensors.

When you include linear deviation over the measuring range, hysteresis, and non-repeatability, you have precision.  You can characterise these measured values, which are pretty much the final average, with a dispersion circle. Where accuracy comes into the equation is when the individual measurement’s average value deviates from the true value. In this instance, the isolated standard error of measurement of pressure sensors characterises solely by the precision. However, the maximum measurement deviation takes both the precision and accuracy into account.

When designing pressure sensors, Baumer specifies the maximum measurement deviation due to it delivering a far more precise specification. It is essential for a sensor to follow this approach when measuring the absolute pressure. This is the same for when referencing is not possible within a measuring system. When carrying out other specifications, often the deviation of the average value from the true value is not identifiable. Alternatively, it might be that it is only identifiable to a certain extent.

Ultimately, Baumer prefers to define the quality of its pressure sensors according to maximum error, as opposed to typical error. Statistics show this to be the best approach for a reliable result.  To back this up, surveys reveal that 99.7% of sensors that underwent tests for maximum error came within specification. In comparison, just 68% of those tested for typical error meet specification.

Temperature dependency and the part it plays

Further to this, an important factor to consider when determining the specification of a pressure sensor is temperature. Whether using maximum measurement deviation or standard error of measurement, both are relative to a reference temperature. This is typically set at 20°C, however, a sensor is rarely used at 20°C or even a constant temperature. The effect of this is that the standard error of measurement and the maximum measurement deviation worsens. This is because the characteristics are only adjustable for one temperature.

When it comes to the application temperature range of the sensors, temperature dependency can strongly influence the maximum measurement deviation. The temperature coefficient zero-point and range both have to be taken into account, depending on the pressure sensor applications involved. In any case, a sensor with a stable temperature is preferred. Baumer develops all its elements according to the stricter definition of temperature dependency. This ensures the reliability and high quality that is necessary for its customers.

For more information about Baumer’s pressure sensor technology or any of their other products visit www.baumer.com.

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The Baumer Group is leading at international level in the development and production of sensors, shaft encoders, measuring instruments as well as components for automatic image processing.

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