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The General Measurement System 3 1.1 Purpose and performance of measurement systems - 3 1.2 Structure of measurement systems 4 1.3 Examples of measurement systems 5 1.4 Block diagram symbols 7 Static Characteristics of Measurement System Elements 9 2.1 Systematic characteristics 9 2.2 Generalised model of a system element 15
- În|G( jn ω1)| sin(n ω1t + φn)
- Sensing element
- Signal conditioning element
- Signal processing element
- Data presentation element
- Conclusion
- 2.4.1 Standards
- 2.4.3 Experimental measurements and evaluation of results
- O versus IM, II at constant I
- Conclusion
- Conclusion
- 4.2 Identification of the dynamics of an element
- Conclusion
- Loading Effects and Two-port Networks
- 5.1 Electrical loading
- 5.2.4 Bilateral transducers
- Conclusion
- 6.1 Introduction
- Multiple earths[1]
- Conclusion
- Reliability, Choice and Economics of Measurement Systems
- 7.1.2 Practical reliability definitions
- Non-repairable items
- Design for reliability
- Maintenance
- Conclusion
where arg G( φn jn = ω1). We work with leading authors to develop the strongest educational materials in engineering, bringing cutting-edge thinking and best learning practice to a global market. Under a range of well-known imprints, including Prentice Hall, we craft high quality print and electronic publications which help readers to understand an...
This is in contact with the process and gives an output which depends in some way on the variable to be measured. Examples are: Thermocouple where millivolt e.m.f. depends on temperature Strain gauge where resistance depends on mechanical strain Orifice plate where pressure drop depends on flow rate. If there is more than one sensing element in a s...
This takes the output of the sensing element and converts it into a form more suit-able for further processing, usually a d.c. voltage, d.c. current or frequency signal. Examples are: Deflection bridge which converts an impedance change into a voltage change Amplifier which amplifies millivolts to volts Oscillator which converts an impedance change...
This takes the output of the conditioning element and converts it into a form more suitable for presentation. Examples are: Analogue-to-digital converter (ADC) which converts a voltage into a digital form for input to a computer Computer which calculates the measured value of the variable from the incoming digital data. Typical calculations are: Co...
This presents the measured value in a form which can be easily recognised by the observer. Examples are: Simple pointer–scale indicator Chart recorder Alphanumeric display Visual display unit (VDU).
This chapter has defined the purpose of a measurement system and explained the importance of system error. It has shown that, in general, a system consists of four types of element: sensing, signal conditioning, signal processing and data presentation elements. Typical examples have been given. 2
The static characteristics of an element can be found experimentally by measuring corresponding values of the input I, the output O and the environmental inputs I and II, when I is either at a constant value or changing slowly. This type of experiment is referred to as calibration, and the measurement of the variables I, O, I and I I must be accura...
The calibration experiment is divided into three main parts.
We first need to find which environmental inputs are interfering, i.e. which affect the zero bias a. The input I is held constant at I IMIN, and one environmental input is = changed by a known amount, the rest being kept at standard values. If there is a result-ing change O in O, then the input I is interfering and the value of the correspond- ∆ I ...
The chapter began by discussing the static or steady-state characteristics of measurement system elements. Systematic characteristics such as non-linearity and environmental effects were first explained. This led to the generalised model of an element. Statistical characteristics, i.e. repeatability and tolerance, were then discussed. The last sect...
This chapter has shown how to find the error of a complete measurement system under steady-state conditions. Measurement error was first defined and then the error probability density function was derived, firstly for a general system of non-ideal elements and then for the typical example of a temperature measurement system. The last section discus...
In order to identify the transfer function G(s) of an element, standard input signals should be used. The two most commonly used standard signals are step and sine wave. This section examines the response of first- and second-order elements to step and sine wave inputs.
The dynamic characteristics of typical measurement system elements were initially discussed; in particular the transfer functions of first- and second-order elements were derived. The response of both first- and second-order elements to step and sine wave inputs was then studied. A general description of the dynamic error of a complete measurement ...
In our discussion of measurement systems no consideration has yet been given to the effects of loading. One important effect is that of inter-element loading where a given element in the system may modify the characteristics of the previous element (for example by drawing current). In turn, the characteristics of this element may be modified by the...
We have so far represented measurement systems as blocks connected by single lines where the transfer of information and energy is in terms of one variable only. Thus in the temperature measurement system of Figure 3.2 the information transfer between elements is in terms of voltage only. No allowance can therefore be made for the amplifier drawing...
Bilateral transducers are associated with reversible physical effects. In a revers-ible effect the same device can, for example, convert mechanical energy into elec-trical energy and also convert electrical energy into mechanical energy. When the device converts electrical energy into mechanical energy it acts as a transmitter or
We have seen how the use of equivalent circuits and two-port networks has enabled both inter-element and process loading effects to be described.
In Chapter 4 we studied the dynamic response of measurement systems to step, sine wave and square wave input signals. These signals are examples of deterministic signals: a deterministic signal is one whose value at any future time can be exactly predicted. Thus if we record these signals for an observation period T (Figure 6.1), the future behavio...
The above explanation assumes an earth plane having a potential of 0 volts at every point on its surface. Heavy electrical equipment can, however, cause currents to flow through the earth, causing different potentials at different points. If the measure-ment circuit is completely isolated from the earth plane there is no problem. In prac-tice, howe...
The chapter began by defining random signals and deterministic signals and explained that in many practical situations the wanted signal may be random. Unwanted sig-nals may also be present in the measurement circuit; these can be classified as either interference (deterministic) or noise (random). The chapter then explained how random signals can ...
In Chapters 3 and 4 we defined the accuracy of a measurement system and explained how measurement error can be calculated, under both steady-state and dynamic con-ditions. Reliability is another important characteristic of a measurement system; it is no good having an accurate measurement system which is constantly failing and requiring repair. The...
Since R(t) and F(t) are dependent on time, it is useful to have measures of reliabil-ity which are independent of time. We will consider two cases: in the first the items are non-repairable and in the second the items are repairable.
Suppose that N individual items of a given non-repairable component are placed in service and the times at which failures occur are recorded during a test interval T. We further assume that all the N items fail during T and that the ith failure occurs at time Ti, i.e. Ti is the survival time or up time for the ith failure. The total up time for N f...
The following general principles should be observed. Element selection. Only elements with well-established failure rate data/models should be used. Furthermore some technologies are inherently more reliable than others. Thus an inductive LVDT displacement sensor (Chapter 8) is inherently more reliable than a resistive potentiometer; the latter inv...
The mean down time, MDT, for a number of items of a repairable element has been defined as the mean time between the occurrence of the failure and the repaired element being put back into normal operation. It is important that MDT is as small as possible in order to minimise the financial loss caused by the element being out of action. There are tw...
The first section of this chapter discussed the reliability of measurement systems. The fundamental principles and practical definitions of reliability were first explained and the relationship between reliability and instantaneous failure rate was derived. The typical variation in instantaneous failure rate throughout the lifetime of an element wa...
This presentation concerns the application of new equalization techniques to professional audio control. The device utilized is a parametric equalizer which: 1) offers vernier control of frequency and amplitude, and coherent control of "Q" or shape, 2) is suitable for automatic voltage control, and 3) improves transient and phase response by ...
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1.4 FUNCTIONAL ELEMENTS OF MEASUREMENT SYSTEM A systematic organization and analysis are more important for measurement systems. The whole operation system can be described in terms of functional elements. The functional elements of generalized measurement system are shown in figure 1.
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Equalizers (used to EQ a sound) come in many variations, the main one being how many bands are available, the more the better, in general. It is useful to think of an equalizer as a set of filters , where each band has a fixed bandwidth, usually defined in octaves and fractions thereof.
When it comes to equalizing your sound, a parametric equalizer (EQ) is one of the most versatile equalizers you can use. That’s because it offers the flexibility to make vastly different types of alterations to the sound of an audio signal.
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This sample file contains explanation and a few examples on measurement system analysis including Gage R & R from Chapter 7 of our Six Sigma Volume 1. For detailed treatment of
