#Time scilab how to#
#Time scilab Pc#

Practically we would want a higher sampling rate, say, 10 times the system bandwidth. This sampling theorem only gives us a lower bound. Here we state only the essence, in plain English: the sampling rate must be at least twice the system bandwidth.

That is in fact an established result, known as the Nyquist-Shannon Sampling Theorem. So, how could we select a proper sampling frequency? Intuitively, we can guess from Figure 3 that if we sample at least twice the frequency of the red sine wave, things should work fine. That happens when the frame rate is too slow relative to the angular velocity of the wheel. Another good example of aliasing is when we watch a movie, sometimes we notice a moving car with its wheels turn in the opposite direction. Undersampling causes the reconstructed signal x'(t) much different from the original. The original signal we want to sample is x(t). Let us investigate what happens if the sampling rate is too low. The memory allocated for data process may be limited. But for embedded control applications, resources are expensive.

#Time scilab Pc#

In a modern desktop PC this does not sound like a problem. The more frequent the sampling, the more data we have to keep. How often should we sample the signal x(t)? Common sense tells us the more frequent, the better, since it is obvious from Figure 6 if the samples x are close together, they should represent x(t) very well. (In some areas of engineering such as communication systems, multi-rate sampling may exist, but for digital control applications there is no use for such complicated schemes.)Ī question follows naturally. The signal x(t) is sampled at fixed time interval Δ, called the sampling period. So, as shown in Figure 2, the continuous signal x(t) has to be sampled into a sequence x, where integer k is the index, or the relative address of data to be selected by the pointer. At one moment in time, a value to be processed is addressed by a data pointer. While a real world signal is continuous, a computer works with values stored in a bank of memory. Before we get into that, an important issue must be addressed. It is described either by difference equations, or by a Z- transfer function. For some motor amplifier that receives a PWM (Pulse-Width-Modulation) input, the PWM unit then replaces the DAC. For instance, motion control applications usually get feedback from motor encoders, which are digital in nature. Note that Figure 1 shows a basic configuration. Nevertheless, it is not difficult to find an external DAC chip with easy interface. Most modern microcontrollers have built-in ADC units, but those with internal DAC’s are rare. The block labeled DAC (Digital-to-Analog Converter) and ADC (Analog-to-Digital Converter) are commonly-used to serve this purpose.

To connect them together, we need additional components to convert the signals from one form to another. Now we have two domains separated by the vertical dotted line i.e., the controller side is discrete, and the plant side is continuous. So the continuous-time feedback diagram in needs to be changed to a hybrid form in Figure 1.

#Time scilab how to#

Show how to use discrete-time transfer function block in an Xcos diagramĪs we all know, most controllers nowadays are implemented digitally.

Learn how to convert from continuous-time to discrete-time system.

Understand sampling process and aliasing problem.

Learn the basics of a digital control system.

This article is contained in Scilab Control Engineering Basics study module, which is used as course material for International Undergraduate Program in Electrical-Mechanical Manufacturing Engineering, Department of Mechanical Engineering, Kasetsart University.