### Glossary of Control Engineering Terms - T

Time Constant: Same as lag time.

Time Response: How the output of a system varies with time (not very exciting if there hasn't been a change in the system input!).

Tracking: When a controller changes a process variable to move the process variable in response to a setpoint change, it is called tracking.

Transfer Function: A convenient way of representing a dynamic system. Rather than working with differential equations, which is difficult even for simple systems, they are converted into the Laplace domain (also called s-domain, since the equations are transformed from written in t (time) to s, which is related to frequency) using a Laplace Transform. This turns the difficult to analyse integration and differentiation functions into multiply and divide functions, making system analysis very much simpler. A transfer function is the ratio of output signal to input signal, so that the output of a system can be calculated by multiplying the input signal by the transfer function. A transfer function usually has numerator and denominator polynomials in powers of s, with the numerator polynomial being of an equal or lower order than the denominator. A discrete time transfer function can also be derived, but this is based on the Z-Transform and is written in powers of z.