Electrical and Electronics. Measurements and Instrumentation. Prithwiraj Purkait. Professor. Department of Electrical Engineering and. Dean, School of. Electronic Instruments for Measuring Basic Parameters: Amplified DC meter, Elements of Electronics Instrumentation and Measurement-3rd Edition by Joshph . Modern Electronic Instrumentation and Measurement Techniques: Helfrick & Cooper Electrical Measurement and Measuring Instruments - Golding & Waddis.
|Language:||English, Spanish, Arabic|
|Genre:||Health & Fitness|
|Distribution:||Free* [*Register to download]|
PDF | On May 16, , Ramaprasad Panda and others published Electrical & Electronics Measurements & Measuring Instruments. Text book Electronic Instrumentation and Measurements David A bell 2nd edition .pdf. Wajeeh Rehman. Loading Preview. Sorry, preview is currently unavailable. Here. – α, the Seebeck coefficient, is a measure of the tendency of electric currents to carry heat and for heat currents to induce electrical currents. – = µ – eφ.
The actual physical assembly may not appear to be so but it can be broken down into a representative diagram of connected blocks.
In the Humidity sensor it is activated by an input physical parameter and provides an output signal to the next block that processes the signal into a more appropriate state. A key generic entity is, therefore, the relationship between the input and output of the block.
As was pointed out earlier, all signals have a time characteristic, so we must consider the behavior of a block in terms of both the static and dynamic states.
The behavior of the static regime alone and the combined static and dynamic regime can be found through use of an appropriate mathematical model of each block. The mathematical description of system responses is easy to set up and use if the elements all act as linear systems and where addition of signals can be carried out in a linear additive manner. Fortunately, general description of instrument systems responses can be usually be adequately covered using the linear treatment.
The equation forG can be written as two parts multiplied together. The other part tells us how that value responds when the block is in its dynamic state.
The static part is known as the transfer characteristic and is often all that is needed to be known for block description. The static and dynamic response of the cascade of blocks is simply the multiplication of all individual blocks. As each block has its own part for the static and dynamic behavior, the cascade equations can be rearranged to separate the static from the dynamic parts and then by multiplying the static set and the dynamic set we get the overall response in the static and dynamic states.
This is shown by the sequence of Equations.
Instruments are formed from a connection of blocks. Each block can be represented by a conceptual and mathematical model. This example is of one type of humidity sensor. This is caused by variations taking place in the parts of the instrumentation over time.
Prime sources occur as chemical structural changes and changing mechanical stresses. Drift is a complex phenomenon for which the observed effects are that the sensitivity and offset values vary. It also can alter the accuracy of the instrument differently at the various amplitudes of the signal present.
Drift is also caused by variations in environmental parameters such as temperature, pressure, and humidity that operate on the components.
They will possess a dynamic component that must be understood for correct interpretation of the results. For example, a trace made on an ink pen chart recorder will be subject to the speed at which the pen can follow the input signal changes. If the transfer relationship for a block follows linear laws of performance, then a generic mathematical method of dynamic description can be used. Unfortunately, simple mathematical methods have not been found that can describe all types of instrument responses in a simplistic and uniform manner.
The behavior of nonlinear systems can, however, be studied as segments of linear behavior joined end to end. Here, digital computers are effectively used to model systems of any kind provided the user is prepared to spend time setting up an adequate model.
Now the mathematics used to describe linear dynamic systems can be introduced. This gives valuable insight into the expected behavior of instrumentation, and it is usually found that the response can be approximated as linear. We begin with the former set: the so-called forcing functions. The most commonly used signals are shown in Figure 3. These each possess different valuable test features. For example, the sine-wave is the basis of analysis of all complex wave-shapes because they can be formed as a combination of various sine- waves, each having individual responses that add to give all other wave- shapes.
The step function has intuitively obvious uses because input transients of this kind are commonly encountered. The ramp test function is used to present a more realistic input for those systems where it is not possible to obtain instantaneous step input changes, such as attempting to move a large mass by a limited size of force.
Forcing functions are also chosen because they can be easily described by a simple mathematical expression, thus making mathematical analysis relatively straightforward. For example, length is a physical quantity.
The metre is a unit of length that represents a definite predetermined length. When we say 10 metres or 10 m , we actually mean 10 times the definite predetermined length called "metre". The definition, agreement, and practical use of units of measurement have played a crucial role in human endeavour from early ages up to this day.
Disparate systems of units used to be very common.
Now there is a global standard, the International System of Units SI , the modern form of the metric system. In trade, weights and measures is often a subject of governmental regulation, to ensure fairness and transparency. Metrology is the science for developing nationally and internationally accepted units of weights and measures.
In physics and metrology, units are standards for measurement of physical quantities that need clear definitions to be useful. Reproducibility of experimental results is central to the scientific method. A standard system of units facilitates this. Scientific systems of units are a refinement of the concept of weights and measures developed long ago for commercial purposes.
Science, medicine, and engineering often use larger and smaller units of measurement than those used in everyday life and indicate them more precisely.
The judicious selection of the units of measurement can aid researchers in problem solving see, for example, dimensional analysis. In the social sciences, there are no standard units of measurement and the theory and practice of measurement is studied in psychometrics and the theory of conjoint measurement. Types of Error : Introduction The knowledge we have of the physical world is obtained by doing experiments and making measurements.
It is important to understand how to express such data and how to analyze and draw meaningful conclusions from it. In doing this it is crucial to understand that all measurements of physical quantities are subject to uncertainties. It is never possible to measure anything exactly.
It is good, of course, to make the error as small as possible but it is always there. And in order to draw valid conclusions the error must be indicated and dealt with properly.
Take the measurement of a person's height as an example. Assuming that her height has been determined to be 5' 8", how accurate is our result?
Well, the height of a person depends on how straight she stands, whether she just got up most people are slightly taller when getting up from a long rest in horizontal position , whether she has her shoes on, and how long her hair is and how it is made up.
These inaccuracies could all be called errors of definition. A quantity such as height is not exactly defined without specifying many other circumstances. Even if you could precisely specify the 13 "circumstances," your result would still have an error associated with it. The scale you are using is of limited accuracy; when you read the scale, you may have to estimate a fraction between the marks on the scale, etc. If the result of a measurement is to have meaning it cannot consist of the measured value alone.
An indication of how accurate the result is must be included also. Indeed, typically more effort is required to determine the error or uncertainty in a measurement than to perform the measurement itself.
Thus, the result of any physical measurement has two essential components: 1 A numerical value in a specified system of units giving the best estimate possible of the quantity measured, and 2 the degree of uncertainty associated with this estimated value.
For example, a measurement of the width of a table would yield a result such as Significant Figures : The significant figures of a measured or calculated quantity are the meaningful digits in it. There are conventions which you should learn and follow for how to express numbers so as to properly indicate their significant figures. Any digit that is not zero is significant. Thus has three significant figures and 1. Zeros between non zero digits are significant. Thus has four significant figures.
Zeros to the left of the first non zero digit are not significant. Thus 0.
This is more easily seen if it is written as 3. For numbers with decimal points, zeros to the right of a non zero digit are significant. Thus 2. For this reason it is important to keep the trailing zeros to indicate the actual number of significant figures. For numbers without decimal points, trailing zeros may or may not be significant.
Thus, indicates only one significant figure. To indicate that the trailing zeros are significant a decimal point must be added. For example, Exact numbers have an infinite number of significant digits. For example, if there are two oranges on a table, then the number of oranges is 2.
Defined numbers 14 are also like this. Low frequency compared with which the instrument was calibrated d. Non inductive shunt in both ammeters and voltmeters b. Non inductive shunt in case of ammeters and are generally self compensated in case of voltmeters c.
Self compensated in case of both ammeters and voltmeters d. Hunting in both ammeters and voltmeters b. Combination of shunt and swamping resistance in both ammeters and voltmeters c. Hunting in case of ammeters and Combination of shunt and swamping resistance in case of voltmeters d. It can be used for ac measurements only b.
Damping is very efficient in case of induction instruments c. Popular Files. June January Trending on EasyEngineering. August Continuous and Discrete By Rodger E. March February October 8.
Never Miss. Load more. Sponsored By. Sharing is Caring.
About Welcome to EasyEngineering, One of the trusted educational blog. Get New Updates Email Alerts Enter your email address to subscribe to this blog and receive notifications of new posts by email.
Search Your Files. Join with us. Content is protected!! July 9.