TIME RESPONSEs OF controlled object

Lecture #3

Functions of an utterance stress

1. Distinctive function. This function manifests itself in differentiating utterances as to their meaning, which is conditioned by the position and type of stress.

- differentiating actual meaning and its syntactical structure

Eg. ˈDon’t you ˈfind it ˊdifficult?

2. Constitutive. Stress form the accentual structure of the utterance, which is the basis of its rhythm.

3. Identificatory. Utterance stress provides the basis for the hearer’s identification of the important parts of the utterance and for the understanding of the content.

When we consider characteristic of control systems we can see two basic operation modes – steady-state condition and transient state. Steady-state condition is characterized by constant value of output signal. Transient state appears when controlled objects pass from one steady-state condition to another.

Figure 3.1. Example - elevator rising from ground to the 4th floor

Time response (or time characteristics) contains more informative and complete data about object behavior than static characteristic. The static characteristic reflects only transforming properties of controlled object due to input signal. While investigation of static characteristic we do not take into consideration signals duration. But time characteristic shows dynamic properties of controlled object with the help of which we can determine the following performances indexes: transient-process time (transition time) - t_tp, system oscillation - s, system overshooting, and number of output signals fluctuations - N.

Figure 3.2. Time characteristic: 1- oscillation, 2- overshooting, 3- normal reaction

Time responseis output signal time variation under the condition that input signal (or disturbing action) varies due to given law (step function or impulse function). Control object must be in steady-state condition before stimulating.

There are two types of input signals when we investigate time characteristic: step function and unit-impulse function.

According to these two types of input signals time responses are divided into two groups: ­ step response and impulse response.

Time responsesof the real control objects are nonlinear.

Step response is object reaction on step function. Control object must be in steady-state condition before step function affect.

The types of object reaction on step function is shown on figure 3.3.

Figure 3.3. Step response

Impulse response is object reaction on unit-impulse function. Control object must be in steady-state condition before unit-impulse function affect.

The types of object reaction on step function is shown on figure 3.4.

Figure 3.4. Impulse response

Time characteristics are obtained in experimental way or with the help of mathematical models calculations. We can manipulate with time characteristic according to superposition principle.

Superposition principle: resulting effect of several independent input influences is the sum of each influence effect.

Superposition principle can be applied only to linear objects or linear control system.

Дата добавления: 2014-01-11