Non-Linearity

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. In reality, no pressure transmitter exactly matches this line; the actual response is a slightly curved line, referred to as the characteristic curve.

Non-linearity is the largest deviation between the actual response and a reference line. There are two common methods for generating this reference line:

●The terminal method, also called the endpoint method, draws a straight line from the actual zero point to the actual full scale value endpoint. Since this method is based on the characteristic curve’s endpoints, it is a truer representation of a pressure transmitter’s non-linearity.

●The best fit straight line (BFSL) method is a straight line that stays within a certain percentage deviation from the characteristic curve, or actual response. The endpoints do not figure into this method. BFSL method values are typically half of terminal method values, meaning that a pressure transmitter with a ±0.25% BFSL non-linearity allows for a ±0.50% error.