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1. Significance of Mechanical Measurement

2. Significance of Mechanical Measurements During the process of measurement , a specific value is assigned to the meaurand by comparing it with a predefined standard It is important to mention over here that while making physical measurements , one needs to keep in mind the measurements are not completely accurate Hence while taking measurements, the uncertainty associated with taking measurements is also considered

3. Classification of Measuring Instruments

4. Generalised Measurement System Measuring Quantity Primary sensing element (sensor) Variable Conversion Element Variable Manipulations Element Data Processing Element Presentation element Observer The Elements of Measurement System are listed below Measuring Quantity Primary Sensing Variable Variable conversion Element Variable manipulation Element Data Transmission Elemet Data Processing Element Data Presentation Element Observer

5. Generalised Measurement System Primary sensing element The quantity under measurement makes it first contact with the primary sensing element of a measuring system The main function of the Primary sensing element is to sense the input variable and gives the output according to the measurand The output is analog electrical signal This is achieve by transducers Variable conversion Element It receives the input from the primary sensing element Conversion of the variable from one form to the other takes place without altering the Input data Its requirement depends upon the measuring instruments, some may need and some may not

6. Generalised Measurement Systems Variable Manipulation Element As per the required Magnification, the input signal is amplified The amplification does not depend upon the Variable conversion element, so the manipulation of variables can process directly without any conversion element in some cases Data Transmission Element Transmission of Data or information from one element to another element takes place in this data transmission element Eg. Data cables , Transmitter and recievers

7. Generalised Measurement Systems Data Processing Element Data is modified before the Final Result Comes. Modification for Final Output Form Modification for some final Calculations Modification for errors in the instruments such as positive error, Zero error , temperature Error Data Presentation Element Finally the data is present to the observer via the Data presentation Element. Eg. Monitor, Recorders, Needle pointers, LCD Observer

8. Types of Input Desired Input These are quantities that the instruments is specifically intended to measure Interfering Input These are quantities to which the intruments are unintentionally sensitive Modifying Input These are quantities which cause a change in the input-output relations for the desired and interfering Inputs

9. Example

10. Static Characteristics Static Calibration Linearity Static sensitivity Accuracy Static error Precision Reproducibility Threshold Resolution Hysterisis Drift Span and Range

11. Dynamic Characteristics Speed of Response and Measuring Lag Fidelity and Dynamic Error Overshoot Dead Time and Dead Zone Frequency Response

12. Static Characteristics Static Calibration Static calibration refers to the procedure where an input ( constant or a variable) is applied to an instrument. Instruments are manufactured based on the property of irreversibility or directionality. This implies that change in an input quantity will cause a corresponding change in the output. Linearity A measuring Instrument / System is said to be linear if it uniformly responds to incremental Changes, that is, the output value is equal to the input value of the measured property over a specified range

13. Static Characteristics Static sensitivity Smallest amount of change that can be detected by the measuring instrument Accuracy Closeness of the measured value to the standard or true value Static error It is the numerical difference between the true value of a quantity and its value as obtained by measurement Precision Precision is a measurement of Repeatability, or consistency, of a measurement It is possible to have a very precise measurement without noise that is repeatable and be considered precise, however it can be inaccurate because of an instrument error Reproducibility It is the deviation that is obtained when the same sample is measured continuously for multiple times with changed measuring conditions

14. Static Characteristics Threshold It is the amount of measurement change before a measuring instrument reacts to a change in measurement output or produces a specified result Resolution It is the smallest increment an Instrument can Detect or Display Hysteresis The maximum difference in output at any measurement value within the sensors specified range when approaching the point first with increasing and then with decreasing pressure Picture on next slide Drift It is a measurement error caused by a gradual shift in a instruments measured value over time Span and Range It can be defined as the range of an instrument from minimum to maximum scale value

15. Hysterisis

16. Dynamic Characteristics Speed of Response it is defined as the rapidity with which an instrument or measurement system responds to changes in measured quantity Response Time It is the time required by the instrument or system to settle to its final steady position after the application of the input Measuring Lag An instrument does not react to a change input immediately The delay in the response of an instrument to a change in the measured quantity is known as measuring lag Lag is of two types : Retardation types and Time delay Fidelity and Dynamic Error Fidelity of a system is defined as the ability of the system to reproduce the output in the same form as the input

17. Dynamic Characteristics Overshoot Moving parts have mass and thus posses inertia. When an input is applied to instruments, the pointer does not immediately come to rest at it steady state position but goes beyond it Over-stood is evaluated as the maximum amount by which moving system moves beyond the steady state position Dead Time and Dead Zone It represents the time before the instrument begins to respond after the measured variable has changed. Frequency Response it is described as the steady state response of a system to a sinusoidal input.

18. Dead Zone

19. Overshoot