ELECTRICAL MEASURMENT AND INSTRUMENTS PREPARED BY: JAYRAJ DESAI (130110109016) SHIVANSH SRIVASTAVA (130110109055) JASMIN DONGA (130110109008) G H PATEL COLLEGE OF ENG. AND TECH.

INSTRUMENTATION CHARACTERISTICS Shows the performance of instruments to be used. Divided into two categories: static and dynamic characteristics. Static characteristics refer to the comparison between steady output and ideal output when the input is constant. Dynamic characteristics refer to the comparison between instrument output and ideal output when the input changes.

1.ACCURACY Accuracy is the ability of an instrument to show the exact reading. Always related to the extent of the wrong reading/non accuracy. Normally shown in percentage of error which of the full scale reading percentage.

2. PRECISION An equipment which is precise is not necessarily accurate. Defined as the capability of an instrument to show the same reading when used each time (reproducibility of the instrument).

Example : X : result Centre circle : true value XXX Low accuracy, high precision XXX XXXX X X X High accuracy, high precision x x Low accuracy, low precision

Accuracy vs Precision High Precision, but low accuracy. There is a systematic error.

Accuracy vs Precision (Cont) High accuracy means that the mean is close to the true value, while high precision means that the standard deviation σ is small.

3. RANGE OF SPAN Defined as the range of reading between minimum value and maximum value for the measurement of an instrument. Has a positive value e.g..: The range of span of an instrument which has a reading range of –100°C to 100 °C is 200 °C.

4. BIAS Constant error which occurs during the measurement of an instrument. This error is usually rectified through calibration. Example : A weighing scale always gives a bias reading. This equipment always gives a reading of 1 kg even without any load applied. Therefore, if A with a weight of 70 kg weighs himself, the given reading would be 71 kg. This would indicate that there is a constant bias of 1 kg to be corrected.

5. SENSIVITY Defined as the ratio of change in output towards the change in input at a steady state condition. Sensitivity (K) = Δθο Δθi Δθο : change in output; Δθi : change in input Example 1: The resistance value of a Platinum Resistance Thermometer changes when the temperature increases. Therefore, the unit of sensitivity for this equipment is Ohm/°C.

Sensitivity Most sensitive Variation of the physical variables

6. DEAD SPACE / DEAD BAND - + Output Reading - + Measured Variables Dead Space Defined as the range of input reading when there is no change in output (unresponsive system).

7. RESOLUTION The smallest change in input reading that can be traced accurately. Given in the form ‘% of full scale (% fs)’. Available in digital instrumentation.

8. THRESHOLD When the reading of an input is increased from zero, the input reading will reach a certain value before change occurs in the output. The minimum limit of the input reading is ‘threshold’.

DYNAMIC CHARACTERISTICS The dynamic inputs are of two types. 1. Transient 2. Steady state Depends on a few standard input signals such as ‘step input’, ‘ramp input’ dan ‘sine-wave input’.

Steady state periodic quantity is one whose magnitude has define reaping time cycle, where as the time variation of a transient magnitude does not repeat. The steady state response is simply response when time reaches infinity. Transient response is a defined as the part of response which goes to zero as time become large.

Dynamic accuracy Dynamic accuracy is refers to measurements made while the inertial unit is moving and not exceeding the measurement range of the individual on-board sensor . (ex. accelerometers, gyroscopes, magnetometers)

Dynamic error Speed of response Dynamic error in a time varying signal resulting from inadequate dynamic response of a transducer. It is the difference between the true value of the quantity changing with time & the value indicated by the measurement system Speed of response It is defined as the rapidity with which a measurement system responds to changes in the measured quantity.

Measuring lag It is the retardation or delay in the response of a measurement system to changes in the measured quantity. The measuring lags are of two types 1).retardation type 2).time delay lag

1).retardation type 2).time delay lag In this case the response of the measurement system begins immediately after the changes in measured quantity has occurred. 2).time delay lag In this case the response of the measurement system begins after dead time after the application of the input.

Fidelity Settling time It is defined as the degree to which a measurement system indicates changes in the measurand quantity without dynamic error . Settling time Time taken for output to reach a steady state value.

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