{"id":10287,"date":"2018-11-09T14:09:48","date_gmt":"2018-11-09T19:09:48","guid":{"rendered":"https:\/\/blog.wika.com\/us\/\/?p=10287"},"modified":"2025-05-15T10:27:09","modified_gmt":"2025-05-15T15:27:09","slug":"pressure-transmitter-accuracy-and-non-linearity","status":"publish","type":"post","link":"https:\/\/blog.wika.com\/us\/knowhow\/pressure-transmitter-accuracy-and-non-linearity\/","title":{"rendered":"Pressure Transmitter Accuracy and Pressure Transmitter Non-Linearity: Not the Same Thing"},"content":{"rendered":"

Sometimes, references to pressure transmitter accuracy are actually about the non-linearity of the pressure transmitter\u2019s response. Although accuracy and non-linearity are related, the two terms are not the same and shouldn\u2019t be used interchangeably. <\/strong><\/p>\n

The market offers a variety of pressure transmitters<\/a>. You choose which one to use based on its features, specifications, and how those fit your requirements. One common customer error, though, is to compare the accuracy of one transmitter with the non-linearity of another. Pressure transmitter accuracy and pressure transmitter non-linearity are not the same thing. To be more precise, non-linearity is but one of the factors when calculating accuracy. And people who confuse the two may end up paying more for less quality.<\/p>\n\n

\"Pressure

There will never be a pressure transmitter that exactly matches the ideal line (in green). The result will always be a slight curve (in red, exaggerated for clarity).<\/p><\/div>\n \n

Ideal vs. Actual Responses<\/h2>\n

To fully explain the difference between pressure transmitter accuracy and non-linearity, one needs to compare the instrument\u2019s ideal response to its actual response.<\/p>\n

The ideal response of a pressure transmitter is graphed as a straight line from the zero point (at 0 psi) to the full scale value, or the upper range, of a pressure transmitter. This can be referred to as the ideal line\u00a0<\/strong>(the green line in Fig. 1). In reality, no pressure transmitter exactly matches this line; the actual response is plotted as a slightly curved line, referred to as the characteristic curve<\/strong>.<\/p>\n

 <\/p>\n\n

\"Calculating

Figure 2: The accuracy of a pressure transmitter is calculated as the largest deviation between its ideal response (green line) and the actual response (red line).<\/p><\/div>\n \n

Accuracy,\u00a0<\/strong>or the maximum measured error, is the largest deviation between the ideal line and the characteristic curve (see Fig. 2).<\/p>\n

 <\/p>\n

\u00a0<\/strong><\/p>\n

\u00a0<\/strong><\/p>\n

 <\/p>\n

\u00a0<\/em><\/p>\n

\u00a0<\/h2>\n

\u00a0<\/h2>\n

How to Calculate Pressure Transmitter Accuracy<\/h2>\n

Manufacturers of pressure transmitters will not define a device\u2019s accuracy with only one variable. Accuracy takes into account several different variables, only one of which is non-linearity. In other words, non-linearity alone does not determine a device\u2019s overall accuracy.<\/p>\n

These are the five variables a user should consider when determining pressure transmitter accuracy:<\/p>\n\n

\"Pressure

Figure 3: Two methods are used to generate the reference line needed to find a pressure transmitter\u2019s non-linearity: the terminal method, also called endpoint method (blue line) and the best fit straight line method (brown line). The linearity is the largest deviation from the reference line to the actual response (red line).<\/p><\/div>\n \n

1. Non-linearity<\/h3>\n

Non-linearity is the largest deviation between the actual response (red curve) and a reference line. There are two common methods for generating this reference line (see Fig. 3):<\/p>\n