Digital Control

Digital Control

 

Introduction

In this study, the general concept digital control will be discussed using 3 to 4 journal articles. At the same time, the implementation of the digital control and various advantages and disadvantages will also be discussed in this study along with the various methods to overcome the disadvantages.

Digital Controller

Digital controller is termed as a branch of control theory that uses the digital computers and act as a system controller. They can also be used as or take a form of the microcontroller as per the needs.  At the same time, it can also take the form of an application-specific integrated circuit as well as a desktop computer. The digital controller system is consisting of two types of conversion the A/D and the D/A.  The A/D converts the analog input to the digital format for the machine and on the other side the D/A converts the digital output to a form that further become an input for the plant or for a digital controller in the form of a pc or a microcontroller.  Now a days there is a need of more reliable, inexpensive and miniaturized computers that are capable to perform the work more effectively and efficiently. The reason behind this is also that people have become more cost sensitive so they find ways to develop more efficient and inexpensive systems (Bonnet et al., 2012). The digital controller systems are flexible, inexpensive, scalable and adaptable. Because of such features they are been used in various control system implementations. The digital control system is flexible in a way that it is very easy to configure as well reconfigure through software. At the same time, scalable means that the programs can be scaled to the limits of the memory without including any extra cost. Adaptable defines that the parameters of the program can be changed with time.

A digital controller is generally poured with a plant in its feedback system. The remaining system is either analog or digital.

The digital controller usually needs:

  • A/D conversion helps to convert analog inputs to machine readable format
  • D/A conversion help to convert the digital outputs to a form that can be an input to a plant.
  • A program can be associate the outputs to the inputs.

The structure of a digital controller system

For controlling a physical system using the digital controller, it is required that the controller should receive measurements form the system and then should process them and after that it send control signals to the actuator that creates an impact on the control action. In most of the applications, both the plant as well as actuator is the analog system (Carlson et al., 2010). This lead to a circumstance where translation is needed as there exist a difference in the language of the controller and the controlled. This translation from the digital to the physical process language (analog) is been done by DAC and vice versa is been performed by ADC.  Further, there is a requirement of a sensor that help to monitor or evaluate the controlled variable for the feedback control. The various combinations of the elements in a control loop is been showed below. The system can also include an inner loop with either analog or digital control.

Advantages of the Digital Controller System

  • Accuracy- The digital signals are been presented in the form of zeros and ones with 12 bits or more than it to represent a single number. This helps to reduce the chances of error as compared to analog signals in which noise is always present.
  • Implementation errors- The digital processing of the control signals involves addition as well as multiplication by the stored numerical values. The errors from the digital representation are negligible.
  • Flexibility- A digital controller system is very flexible as compared to the analog one as the analog is hard to modify as well as redesign once it is been implemented in the hardware. Whereas a digital controller is been implemented in a software and it is easy to modify without even replacing the original controller (Robinson et al., 2010). At the same time, the digital controller system also do not need to follow one or few forms that are been used in the case of analog controller.
  • Speed- As the interval between the samples and the sampling period can be made small so the digital controller is able to achieve the performance easily. This increase in the processing speed also helps to sample and process the control signals at very high speed.
  • Cost- The cost of digital circuitry is decreasing day by day. This is been possible because of the advancement in the technology which made the manufacture easy, instant and reliable and can be offered to the consumers at a relative low price. This in return helped to make the digital controller more economical for the customers as well as the low-cost application users.
  • There is no loss of the signals due to the help of A/D and the D/A conversion.
  • The processing of data has also become easier and straight forward.
  • The typical calculation that earlier was a problem can now be performed much easily.
  • The characteristics of the controller can also be modified easily now just by replacing or changing few programme instructions.
  • The digital processors are much easier to handle as they are more compact and are also not heavy as compared to others.
  • The signal can also be stored and managed for a quite long time and they can also be transmitted easily over a large distance and that too without affecting or creating any impact on the accuracy of the system.

Disadvantages of the Digital Controller System

  • The designing process of the digital control system is not easy, it is a very complex process for achieving an efficient level of performance.
  • Sometimes it is a possibility that there can be few errors in the sampling process (Thomas and Bond, 2013).
  • There is a requirement of the graphic board with digital output which is a limitation.
  • There is also not much availability of models with the digital interfaces.
  • It is difficult to perform fast loops in the case of digital control system.
  • The software interfaces are also not as user friendly as the real knobs as well as the switches.
  • It is also discrete which means that signals might be not accurate as because of the finite word length and there are also time delays in the control loop.
  • It is very difficult to attain high bandwidth.

Method to overcome the disadvantages

Many new models must be developed for digital interface, the designing process should be made simpler, and improvements must be made to attain high bandwidth, network control systems can also help to overcome the disadvantages of the conventional digital control systems mainly at the application level and it helps to bring stability at the same time. Developing a digital strategy can also help to allow more flexibility in the design of the control strategy. This digital strategy will also help to take the benefit of multi-rate sampling which will in return adapt to the instant or rapid changes in the dynamic situations.

Conclusion

From the above report, it is concluded that digital control system is useful to incorporate as compared to the analog systems. Digital controller system is more flexible, scalable and also inexpensive. Hence it is concluded that digital control system is beneficial as it helps to provide accuracy and speed along with this the processing of data has also become easier and straight forward.

References

Bonnet, J., Subsoontorn, P. and Endy, D., 2012. Rewritable digital data storage in live cells via engineered control of recombination directionality. Proceedings of the National Academy of Sciences109(23), pp.8884-8889.

Carlson, E.J., Strunz, K. and Otis, B.P., 2010. A 20 mV input boost converter with efficient digital control for thermoelectric energy harvesting. IEEE Journal of Solid-State Circuits45(4), pp.741-750.

Robinson, M.D., McCarthy, D.J. and Smyth, G.K., 2010. edgeR: a Bioconductor package for differential expression analysis of digital gene expression data. Bioinformatics26(1), pp.139-140.

Thomas, J.G. and Bond, D.S., 2014. Review of innovations in digital health technology to promote weight control. Current diabetes reports14(5), p.485.

 

 

Appendix

Exhibit 1

Digital Control

Exhibit 2

Digital Control

Exhibit 3

Digital Control

Exhibit 4

Digital Control

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