video record
Media not available in the Digital Archive
The programme looks at some of the non-linearities which can be found in control systems. The effects of one of them on the performance of a simple closed-loop servomechanism is examined experimentally.
Metadata describing this Open University video programme
Module code and title: T391, Control engineering
Item code: T391; 08
First transmission date: 27-09-1978
Published: 1978
Rights Statement:
Restrictions on use:
Duration: 00:24:00
+ Show more...
Producer: Edward Smith
Contributors: Dick Fendrich; Tony Pearce
Publisher: BBC Open University
Keyword(s): Control engineering; Home-kit pump; Non-linearities; Saturation
Footage description: Dick Fendrich introduces the programme. He demonstrates an example of a non-linear device, the home experiment kit pump. Input and output voltages of the pump are displayed on an oscilloscope screen. Fendrich points out the saturation effect and shows an idealised version of a saturating element on a graph. Using a chart which has displayed on it input and output wave forms, Fendrich describes a method for conducting a superposition test. Fendrich carries the test into the non-linear region where superposition fails, in order to demonstrate one type of non-linearity - that of saturation. Citing the satellite tracking system from a previous programme as an example of a non-line system, Fendrich explains, with the aid of a graph, how this system can still be modelled by linearising a restricted range of operation. Tony Pearce defines and explains backlash, a commonly encountered non-linearity in geared systems. He uses a model of gear wheels to illustrate his points. The model is connected to an oscilloscope and the backlash trace is displayed on its screen. Looking at a working model of a hydraulic system. Pearce explains the function of the spool valve assembly in the system and then goes on to demonstrate how three spool valves set up nonlinearities. A diagram of the spool valve assembly also helps to illustrate the concept. An oscilloscope trace of the hydraulic ram and diagrams of the system illustrate backlash caused by overlapping spools. Pearce looks at the effect on the above model of a step input. He then compares this response with that for a system without overlap. Both traces are shown on the oscilloscope simultaneously and Pearce examines them in detail, pointing out the differences. With the aid of several graphs, Dick Fendrich makes some general points on ways to redesign a non-linear system to get rid of or to minimise the non-linearity. Fendrich goes on to discuss, briefly, methods for modelling non-linear systems which cannot be redesigned. He uses graphs to illustrate his points. Fendrich sums up.
Master spool number: 6HT/72891
Production number: 00525_5324
Videofinder number: 1102
Available to public: no