What is sensitivity?

The ratio of change between a transducer’s output and input is known as its sensitivity.

For example, a transducer that produces 1 mV for every 100 psi has a sensitivity value of .01 mV/psi. Under ideal conditions, a transducer’s sensitivity value does not change between zero and full scale. A transducer that produces 1 mV for every 100 psi would then, under ideal conditions, also produce 2 mV for an applied pressure of 200 psi, 3 mV for an applied pressure of 300 psi, and so on.

A transducer’s ideal sensitivity can be mapped as a straight line, and the transducer’s sensitivity value, expressed as the ratio of output to input, then equates to the slope of that line.

Ideal Sensitivity is Represented as a Straight Line

Notice also that under ideal conditions, there is zero output when there is zero input.

However, the actual sensitivity of a transducer fluctuates slightly between zero balance and full scale. Some reasons for this might be due to manufacturing and materials imperfections, electrical interference and even the age of the transducer. In addition, a transducer usually produces some amount of output even at zero balance. Thus, true sensitivity actually equates to a non-linear function with a zero offset.

True Sensitivity is Represented as a Curve

Because true sensitivity is non-linear, the true sensitivity value of a transducer (the ratio of output to input) will not always be the same at any point between zero balance and full scale. In order for a sensitivity value to be constant, the sensitivity must be expressed linearly. Most manufacturers use a best fit straight line to represent sensitivity.

Example of a Best Fit Straight Line

The sensitivity value can then be expressed as the slope of the best fit straight line, which becomes the value quoted on the transducer’s calibration certificate.

Sensitivity as the Slope of the Best Fit Straight Line

Note: In some cases, Honeywell uses the slope of a best fit straight line as a transducer’s quoted sensitivity on its calibration certificate. In other cases, Honeywell uses the slope of a terminal point straight line.

See also: What is Non-Linearity?