Deflection method direct measurements are most widely used as. These are
In deflection methods the value of the unknown quality is the determent by the help of measuring instrument having a calibrated scale indicating the quantity under the measurement directly, such as measurement by current by an ammeter. This process is also less time consuming.
A null type instrument as compared to a deflected type instrument has
In null type instrument, a zero or null indication leads to determination of the magnitude of measured quantity. In deflection type instrument the measured quantity produces a mechanical displace in the moving system of the instrument. These type instrument are suited for measurement under dynamic condition. But the null condition dependent upon some other known condition. So the null type instrument are more accurate and highly sensitive as compared to deflection type instrument.
The use of __________________ instruments is merely confined within laboratories as standardizing instrument
Absolute instrument are those instruments which indicate the quantity to be measured in terms of the constants of the instrument and in order to find out the quantity in practical units. No previous calibration or comparison is necessary in this case. So this instrument are rarely use like as the use being merely confined within laboratories as standardizing instruments.
Comparison methods are used
In comparison methods, the value of unknown quantity is determined by direct comparison with a standard of a given quantity. So this methods has a high accuracy of measurement.
Systematic errors are
Systematic errors are the error that remain constant or change according to a definite on repeated measurement of the given quantity. These errors can be evaluated and their influence on the results of measurement can be eliminated by the introduction of proper correction. These are three types of systematic errors – instrumental error and observational error.
The smallest change in measured variable to which instrument will respond is
The resolution of any instrument is the smallest change in the input signal (quantity under measured) which can be detected by the instrument. It may be expressed as an actual value or as a fraction or percentage of the full scale value.
Which following are integrating instruments?
Integrating instrument are those instruments which measure total quantity of electricity delivered in a particular time.
The errors mainly caused by human mistakes are
The errors occur because of mistakes in observed readings, or using instrument and in recording and calculating measurement results. Gross errors are due to human mistake in reading or in using instrument or error in recording observations.
Resolution of an instruments is
Resolution of any instrument is the smallest change in the input signal (quantity under measured) which can detected by instrument. If the input the slowly increased from some arbitrary value it will be noticed that the output does not change at all until the increment exceeds the certain value.
The measured value of a resistance is 10.25 ohm, whereas its value of 10.22 ohm. What is absolute error of the measurement?
Absolute error, δ A = Am - A = measured value - True value.
In measurement system, the function of the signal manipulating elements is to
Manipulation is necessary to change signal level without changing the information contained it for the acceptance of the instruments. The function of the variable manipulation unit is to magnitude the signal presented to it while preserving the original nature of signal.
A pressure measurement instrument is calibrated between 10 bar and 260 bar. The scale span of the instrument is
The lower range of the instrument is 10 bar and upper measurement range of the instrument is 260 bar. So the scale span of the instrument is the difference between upper range and lower range measurement value instrument.
If two meters x and y require 40 mA and 50 mA respectively, to give full scale deflection, then
Resolution of X and Y meters are 40 mA and 50 mA respectively. So X meter is less than resolution of Y meters.
Purely mechanical instrument cannot be used for dynamic measurements because they have
Mechanical instruments are unable to response rapidly to the measurement of dynamic conditions due to the fact that they have moving parts that are rigid, heavy and bulky and consequence have a large mass and they take large response time. Mass presents inertia problems and hence these instrument cannot faithfully follow the rapid changes which are involved in dynamic instrument.
An analog ammeter is
An analog ammeter indicates the magnitude of current at the time when it is being measurement. The indications are given by a pointer moving over a calibrated scale. So an analog meter is an indicating instrument.
In AC circuits, the connection of measuring instruments cause loading effect errors which may effect
The in capability of the system to faithfully measure record or control the measured signal in undistorted form is known as load effect. This results in loading errors. However, under practical conditions; it has been observed that the introduction of any element of system result invariably in extraction of the energy from the system, thereby distorting the original signal. This distortion, phase shift, etc and consequently the ideal measurement becomes impossible.
A wattmeter reads 30.34 watts. The absolute error in the measurement is – 2.22 watt. What is the true value of power?
True value is equal to difference between measured value and absolute error.
A moving coil ammeter has a uniform scale with 50 division and gives a full scale reading 10 A. The instrument can read up to 1/5th of a scale division with a fair degree of certainty. What is the resolution of the instrument in mA?
1 scale division = (10/50) × 100 = 200 mA.
Resolution = (1/5)th of a area scale division = 200/5 = 40 mA.
Relative error is same as
Relative error is the ratio of absolute error to the true value of the unknown quantity to be measured.
A 0-100 V voltmeter has a guaranteed accuracy of 2% of full scale reading. The voltage measured by the voltmeter is 75 volts. The limiting error is in percentage
The magnitude of the limiting error of the instrument = relative error × scale division = 0.02 × 100 = 2 V.
The percentage limiting error at 75 volt is = (2/75) × 100 % = 2.66 %.