Introduction To Feedback (1960)

[Music] plotting a course is one thing holding of course is quite another the control of situations through guiding and steering is among man's greatest accomplishments and yet remains his greatest problem control of this kind usually means first measuring the performance as it is second comparing it with the desired performance third correcting to influence future performance this cycle of measuring evaluating and correcting is called feedback it occurs in simple problems and in complicated ones with such regularity that it has now become a science and an art all our lives we've made use of feedback usually without being aware of it we use it unconsciously much as we use the laws of inertia or the principles of hydraulics or of thermodynamics or those laws of gravity with which we become familiar so early like gravity feedback has been functioning a long time it is feedback that enables this girl to determine the degree to which her hand is not in position to catch the ball and then make the necessary correction we are using feedback when the information gained from one move helps us decide what the next move should be here is the idea information about the past performance or the output of a system is measured and fed back to correct the input of the system so as to affect future performance in this way feedback is the lifeblood of any live performance each change of audience mode is sensed and the performance corrected to compensate feedback answers the question how am i doing if in conversation we find that we are not doing so well the situation can be evaluated and input changed to correct output in a matter of seconds but in Correspondence Control is much more difficult the writer cannot predict precisely what the recipients attitude will be although experience may have given him some idea of the rate of change here feedback is impaired by time lag it is important that information be current and that correction be equal to and opposed to the error a classic mechanical example of feedback is James Watts ball governor for steam engines it measures speed by the degree to which centrifugal force causes the balls to fly apart if speed increases the balls fly farther out and a mechanical linkage transfers this information to a valve which cuts down the steam which slows the shaft which lowers the balls which opens the valve which speeds the shaft which raises the balls which closes the valve and so on it is negative feedback because it opposes what the system is already doing another example of such a closed loop is a conventional heating system temperature down valve open heat on temperature up valve closed heat off in any negative feedback loop some error or oscillation is inevitable but if the system is overactive or unbalanced oscillation can increase until the situation gets out of hand when the correction in a system is greater than and opposed to the error the disturbance in the system tends to increase this type of oscillation leads to panic breakdown and war [Music] when the correction is less than and opposed to the error it tends to damp or decrease the disturbance in the system this is a description of compromise or arbitration in recent years much work has been done on the problem of oscillation in man-made controls results of this work may well suggest means of handling oscillation of other kinds epidemics plagues of insects economic booms and economic slumps the difficulty often comes in telling where the feedback idea can be applied a short look at some simple examples may make the complex ones more recognizable a survey or a poll is feedback in much the same way as any sampling technique or the information that comes from measuring the performance of a model reports to management our feedback however any executive with too many yes-men suffers from impaired feedback animal reflexes feedback so is the activity of a complaint department the return receipt you sign for a registered letter reports back whether or not the message was received as does an examination such two-way communication is essential to give assurance that instruction has been carried out the valve is given the signal to close and the closed valve returns its signal to the control some of these devices will carry into space their own computers to speed and relate their own feedback loops there are cases where a microseconds delay could mean disaster for the system man anticipates reaching some hostile environment of violent contrast yet the interior climate his body must maintain is a highly critical one body temperature can vary but a few degrees the amount of oxygen absorbed the percentage of salt in the blood are critical hundreds of such factors are kept under control by a system of negative feedback loops known as homeostasis homeostasis works constantly to keep the system from deteriorating example when exercise increases carbon dioxide in the blood homeostatic controls increase respiration which lowers the co2 content which in turn will slow down the respiration homeostasis acts to maximize chances of the system survival any conscious control of this closely-knit complex would be impossible but it would be equally impossible for man to manually govern some of the processes of his own invention like the human body this system has its homeostatic feedback loops which keep it from deteriorating and it has its purposeful feedback loops which control process and product in each loop there is a sense organs such as a thermometer a light meter or a speedometer these collect current information which is compared with current requirements any deviation is detected and the correction made the application of the data processor to such systems permits a vast extension of the control art the programmed computer receives current data on the state of the system and the end product it determines proper corrective pattern and feeds information back into the various control loops the byproducts of man's designs create their own need for self-regulating system consider the traffic if it is an open system each motorist gets his own feed and if he is inventive he tries to discover compensating patterns which avoid the congestion but if his new pattern is successful other motorists soon use it too and a new congestion results accumulated data on traffic concentration is of little help the helicopter can provide valuable current information but there are now some closed loop systems that operate in real-time continuous information is gathered from many points this is fed to a computer which is programmed to quickly select the best compensating pattern for each part of the system directing motorists along alternate routes that avoid congestion other congestion x' other problems are being attacked in much the same way in some cases installations which are systems in themselves are linked together to form still larger systems information channels and feedback loops have formed such a vast communications network that we now find ourselves a part of a world community where social and economic changes are taking place at an accelerating rate the same communications responsible for the change give promise for the future this too is feedback it can keep oscillation under control if the information that is received can be made meaningful in time to be effective even at this scale we are perhaps learning to measure learning to relate and learning to correct [Music]