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15:24:52 Page 79
Chapter 3
Measurement System Behavior
3.1 INTRODUCTION
This chapter introduces the concept of simulating measurement system behavior through mathematical modeling. From such a modeling study, the important aspects of measurement system
response that are pertinent to system design and specification can be obtained. Each measurement
system responds differently to different types of input signals and to the dynamic content within
these signals. So a particular system may not be suitable for measuring certain signals or at least
portions of some signals. Yet a measurement system always provides information regardless of how
well (or poorly!) this reflects the actual input signal being measured. To explore this concept, this
chapter discusses system response to certain types of input signals.
Throughout this chapter, we use the term ‘‘measurement system’’ in a generic sense. It refers
either to the response of the measurement system as a whole or to the response of any component or
instrument that makes up that system. Either is important, and both are interpreted in similar ways.
Each individual stage of the measurement system has its own response to a given input. The overall
system response is affected by the response of each stage of the complete system.
Upon completion of this chapter, the reader will be able to
relate generalized measurement system models to dynamic response,
describe and analyze models of zero-, first-, and second-order measurement systems and
predict their general behavior,
calculate static sensitivity, magnitude ratio, and phase shift for a range of systems and input
waveforms,
state the importance of phase linearity in reducing signal distortion,
analyze the response of a measurement system to a complex input waveform, and
determine the response of coupled measurement systems.
3.2 GENERAL MODEL FOR A MEASUREMENT SYSTEM
As pointed out in Chapter 2, all input and output signals can be broadly classified as being static,
dynamic, or some combination of the two. For a static signal, only the signal magnitude is needed to
reconstruct the input signal based on the indicated output signal. Consider measuring the length of a
board using a ruler. Once the ruler is positioned, the indication (output) of the magnitude of length is
immediately displayed because the board length (input) does not change over the time required to
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15:24:52 Page 79
Chapter 3
Measurement System Behavior
3.1 INTRODUCTION
This chapter introduces the concept of simulating measurement system behavior through mathematical modeling. From such a modeling study, the important aspects of measurement system
response that are pertinent to system design and specification can be obtained. Each measurement
system responds differently to different types of input signals and to the dynamic content within
these signals. So a particular system may not be suitable for measuring certain signals or at least
portions of some signals. Yet a measurement system always provides information regardless of how
well (or poorly!) this reflects the actual input signal being measured. To explore this concept, this
chapter discusses system response to certain types of input signals.
Throughout this chapter, we use the term ‘‘measurement system’’ in a generic sense. It refers
either to the response of the measurement system as a whole or to the response of any component or
instrument that makes up that system. Either is important, and both are interpreted in similar ways.
Each individual stage of the measurement system has its own response to a given input. The overall
system response is affected by the response of each stage of the complete system.
Upon completion of this chapter, the reader will be able to
relate generalized measurement system models to dynamic response,
describe and analyze models of zero-, first-, and second-order measurement systems and
predict their general behavior,
calculate static sensitivity, magnitude ratio, and phase shift for a range of systems and input
waveforms,
state the importance of phase linearity in reducing signal distortion,
analyze the response of a measurement system to a complex input waveform, and
determine the response of coupled measurement systems.
3.2 GENERAL MODEL FOR A MEASUREMENT SYSTEM
As pointed out in Chapter 2, all input and output signals can be broadly classified as being static,
dynamic, or some combination of the two. For a static signal, only the signal magnitude is needed to
reconstruct the input signal based on the indicated output signal. Consider measuring the length of a
board using a ruler. Once the ruler is positioned, the indication (output) of the magnitude of length is
immediately displayed because the board length (input) does not change over the time required to
79