While the first order system unconditionally attenuates the input, second order can amplify it in the neighbourhood of the natural frequency for . A nearly uniform frequency response is obtained for S = 0.6 and (Figure 2.23) and this value of the damping factor is commonly used in the design of instruments.

As a rule mechanical systems are second order systems due to their inertia while fluid systems are of first order and electrical systems containing all the three elements , and are of second order. systems are of first order and - systems of zeroth order. A hot-wire anemometer working in the constant temperature mode with feedback will be shown later to be nearly a zeroth order system and hence close to an ideal probe.

The performance of certain probes that are commonly used in thermal sciences are described below by examining their transient behaviour.