E1C01 09/14/2010
15:40:34 Page 1
Chapter 1
Basic Concepts of Measurement
Methods
1.1 INTRODUCTION
We make measurements every day. Consider the common measurements illustrated in Figure 1.1.
We routinely read the temperature of an outdoor thermometer to choose appropriate clothing for
the day. We expect to have exactly 10 gallons or liters of fuel added to our tank when that volume
is indicated on a fuel pump. And we expect measuring cups to yield correct quantities of
ingredients in cooking. We put little thought into the selection of instruments for these routine
measurements. After all, the direct use of the data is clear to us, the type of instruments and
techniques are familiar to us, and the outcome of these measurements is not important enough to
merit much attention to features like improved accuracy or alternative methods. But when the
stakes become greater, the selection of measurement equipment and techniques and the interpretation of the measured data can demand considerable attention. Just contemplate how you might
verify that a new engine is built as designed and meets the power and emissions performance
specifications required.
But first things first. The objective in any measurement is to answer a question. So we take
measurements to establish the value or the tendency of some variable, the results of which are
specifically targeted to answer our question. The information acquired is based on the output of the
measurement device or system. There are important issues to be addressed to ensure that the output
of the measurement device is a reliable indication of the true value of the measured variable. In
addition, we must address the following important questions:
1. How can a measurement or test plan be devised so that the measurement provides the
unambiguous information we seek?
2. How can a measurement system be used so that the engineer can easily interpret the
measured data and be confident in their meaning?
There are procedures that address these measurement questions.
At the onset, we want to stress that the subject of this text is real-life oriented. Specifying a
measurement system and measurement procedures represents an open-ended design problem whose
outcome will not have one particular solution. That means there may be several approaches to
solving a measurement problem, and some will be better than others. This text emphasizes accepted
procedures for analyzing a measurement problem to assist in the selection of equipment,
1
15:40:34 Page 1
Chapter 1
Basic Concepts of Measurement
Methods
1.1 INTRODUCTION
We make measurements every day. Consider the common measurements illustrated in Figure 1.1.
We routinely read the temperature of an outdoor thermometer to choose appropriate clothing for
the day. We expect to have exactly 10 gallons or liters of fuel added to our tank when that volume
is indicated on a fuel pump. And we expect measuring cups to yield correct quantities of
ingredients in cooking. We put little thought into the selection of instruments for these routine
measurements. After all, the direct use of the data is clear to us, the type of instruments and
techniques are familiar to us, and the outcome of these measurements is not important enough to
merit much attention to features like improved accuracy or alternative methods. But when the
stakes become greater, the selection of measurement equipment and techniques and the interpretation of the measured data can demand considerable attention. Just contemplate how you might
verify that a new engine is built as designed and meets the power and emissions performance
specifications required.
But first things first. The objective in any measurement is to answer a question. So we take
measurements to establish the value or the tendency of some variable, the results of which are
specifically targeted to answer our question. The information acquired is based on the output of the
measurement device or system. There are important issues to be addressed to ensure that the output
of the measurement device is a reliable indication of the true value of the measured variable. In
addition, we must address the following important questions:
1. How can a measurement or test plan be devised so that the measurement provides the
unambiguous information we seek?
2. How can a measurement system be used so that the engineer can easily interpret the
measured data and be confident in their meaning?
There are procedures that address these measurement questions.
At the onset, we want to stress that the subject of this text is real-life oriented. Specifying a
measurement system and measurement procedures represents an open-ended design problem whose
outcome will not have one particular solution. That means there may be several approaches to
solving a measurement problem, and some will be better than others. This text emphasizes accepted
procedures for analyzing a measurement problem to assist in the selection of equipment,
1