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The programme looks at the derivation, meaning and interpretation of the root locus, a technique which allows the engineer to predict transient response of a closed loop system.
Metadata describing this Open University video programme
Module code and title: T391, Control engineering
Item code: T391; 05
First transmission date: 28-06-1978
Published: 1978
Rights Statement:
Restrictions on use:
Duration: 00:24:30
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Producer: Edward Smith
Contributors: Chris Dillon; John Monk
Publisher: BBC Open University
Keyword(s): Amplitude ration contour; Block diagram; Bode diagram; Camera position control system; Linear scale
Footage description: John Monk, standing next to a television camera introduces the programme. He explains why the camera position control system must have a smooth transient response. Monk represents a position control system on the block diagram. He then looks at a simplified position control system on a bench in the studio and points out its component parts. Monk goes on to use an analogue computer, rather than the mechanical system above, to perform a frequency response experiment. He builds up a Bode diagram from the results. Monk runs the experiment again this time with an exponentially decaying sinusoid as input. He builds up a Bode diagram from the data. Monk then slots together several Bode diagrams which were obtained as a result of inputting different sorts of decaying sinusoids. By doing this, Monk builds up a surface representing the open-loop amplitude ratio. Chris Dillon shows a model surface which describes the lower frequencies and which uses not a logarithmic scale, as the model above, but a linear scale. Dillon explains how negative frequencies are dealt with on these models. He points out the area of negative frequencies in his model. Dillon goes on to explain the importance of pole positions on the models for determining eigenvalues. These then give information on the system's transient response. John Monk, with experimental apparatus, performs an experiment to see if the prediction for transient response made above holds true in practice. Chris Dillon next goes on to examine the open loop transient response to the closed loop performance of a control system. He uses models and a block diagram of a typical control system to illustrate his points. Dillon points out the regions of 20 dB for amplitude ratio on his model and comes up with an amplitude ration contour. Dillon goes on to look at the requirements of the open loop phase shift, particularly where the phase shift is an odd multiple of 180 . He transfers the data to his model on which the root locus is already drawn. This allows him to determine the link between the open loop amplitude and phase, and the closed loop pole position. He points out that from this he can predict the closed loop transient response. John Monk, with experimental apparatus and a model predicts the transient response of a system from looking at a surface which has the root locus plotted. Monk goes on to run the experiment and comments on the accuracy of his prediction. He then makes another prediction for a higher controller gain, again runs the experiment and comments on the results. Monk sums up the programme by running a third experiment and comparing it with his prediction.
Master spool number: 6HT/72794
Production number: 00525_5321
Videofinder number: 1099
Available to public: no