Friday, August 1, 2014

Control System

Control System
Control System is that means by which any quantity of interest in a machine, mechanism or other equipment is maintained or altered in accordance with a desired manner.
1. Closed loop control: The information about the instantaneous state of the output is feedback to the input and is used to modify it in such a manner as to achieve the desired output.
2. Open loop  control: Any physical system which does not automatically correct for variation in its output.
In modern usage the term servomechanism  or servo is restricted to feedback control systems in which the controlled variable is mechanical position or time derivative of position. Example: velocity and acceleration.
A servo system is used to position a load shaft in which driving motor is geared to load to be moved.
Historical Development of Automatic Control
The first automatic control system, the fly ball governor, to control the speed of steam engines, was invented by James Watt in 1770.
About hundred years later Maxwell analyzed the dynamics of fly ball governor.
In early 1920, Minor Sky performed the classic work on the automatic Steering of ships and positioning of guns on shipboards.
The word 'servo' has originated with Hazen's work in 1934.
Sampled Data and Digital Control Systems
Sampled data and digital systems differ from these continuous data systems in that the signals at one or more points of the system are either in form of a pulse train or digital code.
The term discrete data control system is often used to describe these systems.
Non-linear Systems
The important features of non-linear system performance may be completely overlooked if they are analyzed and designed through linear techniques as such.

Wednesday, April 2, 2014

Biomedical Instrumentation

Bio-medical engineering is aimed at keeping people healthy and helping to cure them when they are ill. In general, them term bio-medical is used for the field. The term, bio-medical instrumentation is used for the methods of measurement within the field. The electrocardiograph first used by Einthoven at the end of nineteenth century. Physiological parameters are not measured in the same way as physical parameters. The branch of science that includes the measurements of physiological variables and parameters is known as biometrices. Bio-medical instrumentation provides the tools by which these measurements can be achieved.
Bio-medical Instrumentation is to aid the medical clinician and researcher in devising ways of obtaining reliable and meaningful measurements from living human being.
Man Instrument System
The overall system, which includes both the human organism and the instrumentation required for the measurement of human.
Component of Man Instrument System
Subject, Stimulus, Transducer, Signal Conditioning equipment, Display Equipment, 'Recording, Data Processing and Transmission Equipment' and Control Devices. 
Objective and Goal
Information gathering, Diagnosis, Evaluation, Monitoring, Control. The Goal is to make possible the measurement of information communicated by the various elements of human body.
  1. Clinical - It is devoted to the diagnosis, care and treatment of patients.
  2. Research -It is used primarily in the search for new knowledge pertaining to the various systems that compose the human organism. 
Types of Measurements
  1. Vivo - It is made on or within the living organism itself. For Example - A device inserted into the blood stream to measure the pH of the blood directly.
  2. Vitro - It is performed outside the body, even though it relates to the functions of the body. For Example - pH of a sample of blood.
Major Physiological Systems of the body
  1. The Bio-chemical System - Chemical Systems that produce energy for the activity of the body, messenger agents for communication, materials for body repair and growth and substances required to carry out the various body functions.
  2. The Cardiovascular System - A complex, closed hydraulic system with a four chamber pump i.e. the Heart, connected to flexible and sometimes elastic tubing i.e. blood vessels.
  3. The Respiratory System - The pneumatic system of the body. 
  4.  The Nervous System - Communication network for the body. If a certain section is damaged, other section can adapt and eventually take over the function of the damaged section.
Problems encountered in measuring a living system 
  1. Inaccessibility of variables to measurements.
  2. Variability of the data. 
  3. Lack of knowledge about interrelationships.
  4. Interaction among physiological systems.
  5. Effect of the transducer on the measurement.
  6. Energy limitations.
  7. Safety considerations.
Leslie Cromwell, Fred J. Weibell, Erich A. Pfeiffer, "Biomedical Instrumentation and Measurements", Pearson Education.