Static And Dynamic Characteristics Of Measurement Systems PdfBy Paige F. In and pdf 12.05.2021 at 08:19 6 min read
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- 3.1 Static Characteristics of Instrument Systems
- Static and Dynamic Characteristics of Instruments
- Instrumentation and Process Control
- Performance Characteristics
3.1 Static Characteristics of Instrument Systems
The last three are, of course, closely related. Basic to the whole idea of weights and measures are the concepts of uniformity, units, and standards. Uniformity, the essence of any system of weights and measures, requires accurate, reliable standards of mass and length. 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.
If nonlinearity exists in elements, then it becomes considerably more difficultperhaps even quite impracticalto provide an easy to follow mathemat-ical explanation. 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. One expresses the static behavior of the block, that is, the value it has after all transient time varying effects have settled to their final state. 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. Detailed description of drift is not at all easy but it is possible to work satisfactorily with simplified values that give the average of a set of observations, this usually being quoted in a conservative manner. The first graph a in Figure Drift is also caused by variations in environmental parameters such as temperature, pressure, and humidity that operate on the components.
These are known as influence parameters. An example is the change of the resistance of an electrical resistor, this resistor forming the critical part of an electronic amplifier that sets its gain as its operating temperature changes. Unfortunately, the observed effects of influence parameter induced drift often are the same as for time varying drift. Appropriate testing of blocks such as electronic amplifiers does allow the two to be separated to some extent.
For example, altering only the temperature of the amplifier over a short period will quickly show its temperature dependence. Drift due to influence parameters is graphed in much the same way as for time drift.
Figure shows the drift of an amplifier as temperature varies. Note that it depends significantly on the temperature Drift in the performance of an instrument takes many forms: a drift over time for a spring balance; b how an electronic amplifier might settle over time to a final value after power is supplied; c drift, due to temperature, of an electronic amplifier varies with the actual temperature of operation.
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. Drift in the performance of an instrument takes many forms: a drift over time for a spring www. 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. 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.
Error Analysis : IntroductionThe 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 "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 www. 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,
Static and Dynamic Characteristics of Instruments
The static characteristics of instruments are attributes that changes slowly with time. Static characteristics can be divided in to desirable and undesirable. The true length of a steel beam is 6 m. Three repeated readings with a laser meter indicates a length of 6. The accuracy based on maximum difference can be calculated as. Example - for the steel beam above the mean value of the set of measurements is 6.
Peter H. Before we can begin to develop an understanding of the static and time changing characteristics of measurements, it is necessary to build a framework for understanding the process involved, setting down the main words used to describe concepts as we progress. The basic entity needed to develop the knowledge is called data , and it is obtained with physical assemblies known as sensors that are used to observe or sense system variables. The terms information and knowledge tend to be used interchangeably to describe the entity resulting after data from one or more sensors have been processed to give more meaningful understanding. The individual variables being sensed are called measurands.
The characteristics of measurement instruments which are helpful to know the performance of instrument and help in measuring any quantity or parameter, are known as Performance Characteristics. Performance characteristics of instruments can be classified into the following two types. The characteristics of quantities or parameters measuring instruments that do not vary with respect to time are called static characteristics. Sometimes, these quantities or parameters may vary slowly with respect to time. Following are the list of static characteristics. The term, static error signifies the inaccuracy of the instrument. If the static error is represented in terms of percentage, then it is called percentage of static error.
Instrumentation and Process Control
Skip to Main Content. A not-for-profit organization, IEEE is the world's largest technical professional organization dedicated to advancing technology for the benefit of humanity. Use of this web site signifies your agreement to the terms and conditions. A test method for the static and dynamic characteristics of servo-motor-pumps Abstract: A test method for dynamic and static performances of Servo-Motor-Pumps SMP was proposed.
Measuring instruments are the device which indicates the measured quantity into a broadly displayed information. A measuring instrument can directly show the measured value or it can show the equivalent value to known measure value of the same quantity. To do the perfect performance, an instrument should have some quality, here in this article we will discuss that. In this article we broadly classified the characteristic of an instrument in two types:.
Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. DOI: Omer and M. Omer , M. In this paper, the major static characteristic parameters for sensors and instruments are defined and explained.
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Hysteresis and Backlash
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