Linearity is the relationship between output voltage and the mechanical rotation of the shaft. Linearity is a specific type of conformity where the theoretical function (ideal output curve) is a straight line. specified in one of 4 ways: absolute, independent, zero based or terminal based.
- Absolute - Absolute linearity is the maximum permissible deviation of the actual output curve from a fully defined straight reference line. It is expressed as a percentage of the total applied input voltage and measured over the theoretical electrical travel. An index point on the actual output is required.
- Independent - Independent linearity is the maximum permissible deviation of the actual output curve from a reference line. The slope and position of this reference line arc chosen to minimize deviations over all or a portion of the actual electrical travel. In other words, the choice of the values for the slope and intercept arc such as to minimize the linearity error. Thus. the reference line is placed for best straight line fit through the actual output curve. Further restrictions may be imposed on the limits of slope and intercept by additionally specifying the range of permissible end output ratios.
- Zero Based - Zero based linearity is a special case of independent linearity where the zero travel end of the theoretical reference line is specified. In this case, the theoretical reference line extends over the actual electrical travel. Zero based linearity is the maximum resulting deviation of the actual output from the straight reference line. This straight line is drawn through the specified minimum output voltage ratio with a slope chosen to minimize deviations from the actual output.
- Terminal Based - A linearity specification sometimes used with wire-wound potentiometers is terminal based linearity. It is the maximum deviation of the actual output from a straight reference line drawn through minimum and maximum end points. These points arc separated by the actual electrical travel. Unless otherwise stated, the minimum and maximum output ratios are, respectively. zero and 100% of the total applied input voltage. Terminal based linearity is expressed as a percentage of the total applied input voltage.
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For a complete breakdown including math equations please see Bourns® Potentiometers (Beginning on page 40) and review Bourns_pot_linearity_technote.pdf