Characteristic Curves

Proportional behaviour between the input and output quantity of a measurement system with the formula y = m ∙ x looks like this:

Ideal characteristic of a thermometer: output “25 °C”, “50 °C” and “75 °C” at 25 °C, 50 °C and 75 °C — Ausgabe = output · Physikalischer Wert = physical value

The output quantity of the measurement system is the output of the value to a digital interface or the display for a human being. Here I have chosen a string “50°C” for output on a display; it could also be a digital numerical value that another system interprets as 50 °C.

The input is always a physical value that is to be measured. With proportional behaviour, transfer functions – as discussed in the previous chapter – can be multiplied to give a transfer function of the overall system. Unfortunately, not all transfer functions are proportional. This chapter discusses common deviations from proportional behaviour.