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15:40:34 Page 4
associated with hot days, ‘‘100
F in the shade’’ implies a specific sensor placement. Accordingly,
the interpretation of all information passed through and indicated by the system depends on what is
actually sensed by the sensor. For example, the interpretation of the output of a medical thermometer
depends on where its sensor is placed.
Output Stage
The goal of a measurement system is to convert the sensed information into a form that can be
easily quantified. Consider a familiar example, the liquid-in-glass bulb thermometer. The liquid
contained within the bulb on the common bulb thermometer of Figure 1.4 exchanges energy with
its surroundings until the two are in thermal equilibrium. At that point they are at the same
temperature. This energy exchange is the input signal to this measurement system. The phenomenon of thermal expansion of the liquid results in its movement up and down the stem, forming an
output signal from which we determine temperature. The liquid in the bulb acts as the sensor.
By forcing the expanding liquid into a narrow capillary, this measurement system transforms
thermal information into a mechanical displacement. Hence, the bulb’s internal capillary design
acts as a transducer.
The output stage indicates or records the value measured. This might be a simple readout
display, a marked scale, or even a recording device such as a computer disk drive. The readout scale
of the bulb thermometer in Figure 1.4 serves as the output stage of that measurement system.
It is worth noting that the term ‘‘transducer’’ is also often used in reference to a packaged
device, which may contain a sensor, transducer, and even some signal conditioning elements. While
such terminology is not true to our presentation, the context in which the term is used prevents
ambiguity.
2 0
3 0
4 0
5 0
6 0
7 0
Output stage
Sensor–transducer stage
Sensor
Bulb
Display scale
Stem
Figure 1.4 Components of bulb thermometer
equivalent to sensor, transducer, and output
stages.
4 Chapter 1 Basic Concepts of Measurement Methods
15:40:34 Page 4
associated with hot days, ‘‘100
F in the shade’’ implies a specific sensor placement. Accordingly,
the interpretation of all information passed through and indicated by the system depends on what is
actually sensed by the sensor. For example, the interpretation of the output of a medical thermometer
depends on where its sensor is placed.
Output Stage
The goal of a measurement system is to convert the sensed information into a form that can be
easily quantified. Consider a familiar example, the liquid-in-glass bulb thermometer. The liquid
contained within the bulb on the common bulb thermometer of Figure 1.4 exchanges energy with
its surroundings until the two are in thermal equilibrium. At that point they are at the same
temperature. This energy exchange is the input signal to this measurement system. The phenomenon of thermal expansion of the liquid results in its movement up and down the stem, forming an
output signal from which we determine temperature. The liquid in the bulb acts as the sensor.
By forcing the expanding liquid into a narrow capillary, this measurement system transforms
thermal information into a mechanical displacement. Hence, the bulb’s internal capillary design
acts as a transducer.
The output stage indicates or records the value measured. This might be a simple readout
display, a marked scale, or even a recording device such as a computer disk drive. The readout scale
of the bulb thermometer in Figure 1.4 serves as the output stage of that measurement system.
It is worth noting that the term ‘‘transducer’’ is also often used in reference to a packaged
device, which may contain a sensor, transducer, and even some signal conditioning elements. While
such terminology is not true to our presentation, the context in which the term is used prevents
ambiguity.
2 0
3 0
4 0
5 0
6 0
7 0
Output stage
Sensor–transducer stage
Sensor
Bulb
Display scale
Stem
Figure 1.4 Components of bulb thermometer
equivalent to sensor, transducer, and output
stages.
4 Chapter 1 Basic Concepts of Measurement Methods