5 Discrete-time systems

5.1 The z-transform

So far, we have considered systems which behave as a continuous function of time, t. The main vehicle for the analysis of these systems has been the Laplace transform. In continuous-time systems, the feedback signal is converted to a control signal using an analogue controller whose output is a smooth continuous function of time. Today, few electromechanical analogue control systems exist in HVAC control – these having mostly given way to stand-alone application-specific or universal digital controllers (see section 1.3).

Digital control systems are constrained by the finite time taken for feedback data to be converted from analogue measurement to digital number and then processed to form a control ...

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