Mechanical Guru's

PROPORTIONAL CONTROL SYSTEM Proportional control action In a proportional control action, there is a continuous linear relation between the output m (t) and the actual error signal e (t). Evidently the control valve or the regulating unit can take up any position right from the fully open to fully closed. Depending upon the shift of the measured variable from the desired value, an adjustment is made of the amount of energy supplied (i.e., the manipulated variable) to the process or plant. The change in the valve position is proportional to the amount of deviation and is not affected by the rate or duration of the deviation. The proportional control follows the law:                                                   ...

SELECTING AN MEASURING INSTRUMENT THE SELECTION OF AN INSTRUMENT FOR A SPECIFIC MEASUREMENT APPLICATION REQUIRES THE CONSIDERATION OF SEVERAL FACTORS THE FOLLOWING BEING CERTAINLY FUNDAMENTAL TO ENTIRE PHILOSOPHY OF MEASUREMENT AND INSTRUMENT SELECTION. MAXIMUM AND MINIMUM VALUES THE INPUT VARIABLES ARE EXPECTED TO ASSUME - THE INSTRUMENT RANGE MUST EQUAL TO THE EXPECTED RANGE OF VARIABLE TO BE MEASURED. EXCESSIVE INSTRUMENT RANGE MEANS A LOT OF READABILITY.FOR A WIDE RANGE IN THE VARIABLE, MULTIPLE RANGE OF INSTRUMENT ARE DESIRED. NATURE OF THE INPUT SIGNAL -  IS IT CONSTANT OR TIME DEPENDENT? IF TIME VARIANT, THEN WHETHER VARIATION IS PERIODIC, TRANSIENT OR RANDOM. FOR TRANSIENT MEASUREMENT, IT IS TO BE ENSURED THAT NATURAL FREQUENCIES AND TIME CONSTANTS ARE PROPERLY SELECTED. NON INTERFERENCE WITH MEASURING SYSTEM - THE BASIC PRINCIPAL OF MEASURING IS THAT THE ACT SHOULDN'T AFFECT THE QUANTITY BEING MEASURED. OUR JOB IS TO SEE THAT THE INSTRUMENT OF...

MEASUREMENT AND ITS TYPE MEASUREMENT: MEASUREMENT IS USED TO TELL US THE LENGTH, THE WEIGHT, THE TEMPERATURE, OR A CHANGE IN ONE OF THESE PHYSICAL ENTITIES OF A MATERIAL. IT IS THE RESULT OF AN OPINION FORMED BY ONE OR MORE OBSERVERS ABOUT THE RELATIVE SIZE OR INTENSITY OF SOME PHYSICAL QUANTITY. THE OPINION IS FORMED BY THE OBSERVER AFTER COMPARING THE OBJECT WITH A QUANTITY OF SAME KIND CHOSEN AS A UNIT, CALLED  STANDARD. THE RESULT OF MEASUREMENT IS EXPRESSED BY A NUMBER REPRESENTING THE RATIO OF THE UNKNOWN QUANTITY TO THE ADOPTED STANDARD. FOR EXAMPLE, 10 CM LENGTH OF AN OBJECT IMPLIES THAT THE OBJECT IS 10 TIMES AS LARGE AS 1 CM; THE UNIT EMPLOYED IN EXPRESSING LENGTH. TYPE OF MEASUREMENT MEASUREMENTS ARE DIVIDING IN TO THREE CATEGORIES DIRECT AND INDIRECT MEASUREMENTS DIRECT MEASUREMENTS THE VALUE OF THE PHYSICAL PARAMETER (MEASURAND) IS DETERMINED BY COMPARING IT DIRECTLY WITH REFERENCE STANDARDS. THE PHYSICAL QUANTITIES LIKE MASS, LENGTH, AND TI...

MAINTENANCE AND ITS TYPES MAINTENANCE:- MAINTENANCE INVOLVES KEEPING THE WORKPLACE, ITS STRUCTURES, EQUIPMENT, MACHINES, FURNITURE AND FACILITIES IN GOOD REPAIR AND OPERATING EFFICIENTLY AND SAFELY BREAKDOWN MAINTENANCE IT MEANS THAT PEOPLE WAITS UNTIL EQUIPMENT FAILS AND REPAIR IT. SUCH A THING COULD BE USED WHEN THE EQUIPMENT FAILURE DOES NOT SIGNIFICANTLY AFFECT THE OPERATION OR PRODUCTION OR GENERATE ANY SIGNIFICANT LOSS OTHER THAN REPAIR COST. PREVENTIVE MAINTENANCE IT IS A DAILY MAINTENANCE (CLEANING, INSPECTION, OILING AND RE-TIGHTENING), DESIGN TO RETAIN THE HEALTHY CONDITION OF EQUIPMENT AND PREVENT FAILURE THROUGH THE PREVENTION OF DETERIORATION, PERIODIC INSPECTION OR EQUIPMENT CONDITION DIAGNOSIS, TO MEASURE DETERIORATION. IT IS FURTHER DIVIDED INTO PERIODIC MAINTENANCE AND PREDICTIVE MAINTENANCE. JUST LIKE HUMAN LIFE IS EXTENDED BY PREVENTIVE MEDICINE, THE EQUIPMENT SERVICE LIFE CAN BE PROLONGED BY DOING PREVENTIVE MAINTENANCE. ...

LINEARITY THE WORKING RANGE OF MOST OF THE INSTRUMENT PROVIDES A LINEAR RELATIONSHIP BETWEEN THE OUTPUT (READING TAKEN FROM THE SCALE OF THE INSTRUMENT) AND INPUT (MEASURED, SIGNAL PRESENTED TO THE MEASURING SYSTEM). THE ASPECT TENDS TO FACILITATE A MORE ACCURATE DATA REDUCTION. LINEARITY IS DEFINED AS THE ABILITY TO REPRODUCE THE INPUT CHARACTERISTICS SYMMETRICALLY, AND THIS CAN BE EXPRESSED BY THE STRAIGHT LINE EQUATION  Y=MX+C WHERE Y IS THE OUTPUT, X IS THE INPUT, M IS THE SLOPE AND C IS THE INTERCEPT.APPARENTLY, THE CLOSENESS OF THE CALIBRATION CURVE TO A SPECIFIED STRAIGHT LINE IS THE LINEARITY OR THE INSTRUMENT. ANY DEPARTURE FROM THE STRAIGHT-LINE RELATIONSHIP IS NON-LINEARITY. THE NON-LINEARITY MAY BE DUE TO: * NON-LINEARITY ELEMENTS IN THE MECHANICAL DEVICE * MECHANICAL HYSTERESIS * VISCOUS FLOW OR CREEP, AND * ELASTIC AFTER EFFECTS IN THE MECHANICAL SYSTEM IN A NOMINALLY LINEAR MEASUREMENT DEVICE, THE NON-LINEARITY MAY TAKE DIFFERENT FORM...

ERROR DESPITE UTMOST CARE AND PRECAUTIONS AN EXPERIMENTER MAY TAKE TO ELIMINATE ALL POSSIBLE ERRORS, THE HAPPY GOAL IS SELDOM ATTAINED AND CERTAIN ERRORS ARE BOUND TO CREEP IN FOR EXAMPLE, EVEN IN AN APPARENTLY   SIMPLE MEASUREMENT OF FLOW VELOCITY WITH A PITOT TUBE ANY MISALIGNMENT OF THE PROBE, LEAKS IN THE PRESSURE TUBING, CHANGES IN THE BORE AND SURFACE CONDITIONS OF THE MANOMETER, ANY FLUCTUATIONS IN THE ATMOSPHERIC AND STREAM PRESSURE ARE LIKELY TO AFFECT THE PROBE READINGS AND GIVE RISE TO UNCERTAINTIES .ERRORS AND UNCERTAINTIES ARE INHERENT IN THE PROCESS OF MAKING ANY MEASUREMENT AND IN THE INSTRUMENT WITH WHICH THE MEASUREMENT ARE MADE. A STUDY OF ERROR IS IMPORTANT AS A STEP IN FINDING WAYS OF REDUCING THEM, AND ALSO AS MEANS OF ESTIMATING THE RELIABILITY OF FINAL RESULTS. THIS CHAPTER PROVIDES A BRIEF DISCUSSION ABOUT THE NATURE OF ERRORS AND STATISTICAL ACCURACY OF TEST RESULTS.

HYDRAULIC CONTROL VALVES THESE ELEMENTS OF A HYDRAULIC CONTROL SYSTEM FUNCTION TO REGULATE THE FLOW OF HYDRAULIC FLUID FROM THE HIGH PRESSURE SIDE TO THE ACTUATOR, I.E. THE HYDRAULIC MOTOR. THERE ARE THREE MAIN TYPES OF VALVES. ·          THE PISTON OR SPOOL TYPE ·          THE FLAPPER AND NOZZLE TYPE ·          THE JET PIPE VALVE IN ALL CASES, THE MECHANICAL INPUT MOTION CAN BE CONTROLLED BY MANUAL OPERATION, OR BY A LIMITED MOTION CAN BE CONTROLLED BY MANUAL OPERATION, OR BY A LIMITED MOTION ELECTRIC MOTOR, OR BY HYDRAULIC PILOT METHOD. THE OUTPUT RESULTS IN A CHANGE OF HYDRAULIC PRESSURE. PISTON OR SPOOL VALVE:   THE COMMONLY USED SPOOL VALVE IS CONSTRUCTED IN EITHER A THREE-WAY OR A FOUR-WAY VALVE ARRANGEMENT WHEN THE SPOOL IS IN THE NEUTRAL POSITION, THE OIL FLOW TO THE ACTUATOR IS COMPLETELY BLOCKED. DISPLACEMENT OF THE SPOOL TO RIGHT...

CONTROL  SYSTEMS INTRODUCTION THE KEY CHARACTERISTIC OF CONTROL IS TO INTERFERE, TO INFLUENCE OR TO MODIFY THE PROCESS. THIS CONTROL FUNCTION OR THE INTERFERENCE TO THE PROCESS IS INTRODUCED BY AN ORGANIZATION OF PARTS (INCLUDING OPERATORS IN MANUAL CONTROL) THAT, WHEN CONNECTED   TOGETHER IS CALLED THE  CONTROL SYSTEM .  DEPENDING ON   WHETHER A HUMAN   BODY (THE OPERATOR) IS PHYSICALLY INVOLVED IN THE CONTROL SYSTEM, THEY ARE DIVIDED INTO    MANUAL CONTROL  AND  AUTOMATIC CONTROL . DUE TO ITS EFFICIENCY, ACCURACY AND RELIABILITY, AUTOMATIC CONTROL IS WIDELY USED IN CHEMICAL PROCESSED. THE AIM OF THIS SECTION IS TO INTRODUCE THE CONCEPT OF CONTROL SYSTEMS, WHAT THEIR FUNCTION IS AND WHAT HARDWARE AND SOFTWARE IS REQUIRED BY THEM. MANUAL  CONTROL SYSTEM FIRST START WITH A SIMPLE MANUAL CONTROL SYSTEM, TO EXAMINE HOW CONTROL IS INTRODUCED, HOW THE CONT...