E1C06 09/14/2010
11:55:2 Page 209
Chapter 6
Analog Electrical Devices
and Measurements
6.1 INTRODUCTION
This chapter provides an introduction to basic electrical analog devices used with analog signals or
to display signals in an analog form. We include analog output meters and the more common solidstate devices used in signal conditioning. Information is often transferred between stages of a
measurement system as an analog electrical signal. This signal typically originates from the
measurement of a physical variable using a fundamental electromagnetic or electrical phenomenon
and then propagates from stage to stage of the measurement system (see Fig. 1.1). Accordingly, we
discuss some signal conditioning and output methods.
While analog devices have been supplanted by their digital equivalents in many applications,
they are still widely used and remain engrained in engineered devices. An analog output format is
often ergonomically superior in monitoring, as evidenced by modern car speedometer dials and dial
wristwatches. Too often we qualify a digital device by its digital readout, but internal analog circuits
form the foundation for both analog and many digital indicating systems. In fact, many of the
systems that we interface with are analog and digital hybrids. Within a signal chain, it is common to
find digital and analog electrical devices being used together and so requiring special signal
conditioning. An understanding of analog device function provides insight, as well as a historical
reference point, into the advantages and disadvantages of digital counterparts; such issues are
discussed in this chapter.
Upon completion of this chapter, the reader will be able to
understand the principles behind common analog voltage and current measuring
devices,
understand the operation of balanced and unbalanced resistance bridge circuits,
define, identify, and minimize loading errors,
understand the basic principles involved in signal conditioning, especially filtering and
amplification, and
apply proper grounding and shielding techniques in measuring system hookups.
209
11:55:2 Page 209
Chapter 6
Analog Electrical Devices
and Measurements
6.1 INTRODUCTION
This chapter provides an introduction to basic electrical analog devices used with analog signals or
to display signals in an analog form. We include analog output meters and the more common solidstate devices used in signal conditioning. Information is often transferred between stages of a
measurement system as an analog electrical signal. This signal typically originates from the
measurement of a physical variable using a fundamental electromagnetic or electrical phenomenon
and then propagates from stage to stage of the measurement system (see Fig. 1.1). Accordingly, we
discuss some signal conditioning and output methods.
While analog devices have been supplanted by their digital equivalents in many applications,
they are still widely used and remain engrained in engineered devices. An analog output format is
often ergonomically superior in monitoring, as evidenced by modern car speedometer dials and dial
wristwatches. Too often we qualify a digital device by its digital readout, but internal analog circuits
form the foundation for both analog and many digital indicating systems. In fact, many of the
systems that we interface with are analog and digital hybrids. Within a signal chain, it is common to
find digital and analog electrical devices being used together and so requiring special signal
conditioning. An understanding of analog device function provides insight, as well as a historical
reference point, into the advantages and disadvantages of digital counterparts; such issues are
discussed in this chapter.
Upon completion of this chapter, the reader will be able to
understand the principles behind common analog voltage and current measuring
devices,
understand the operation of balanced and unbalanced resistance bridge circuits,
define, identify, and minimize loading errors,
understand the basic principles involved in signal conditioning, especially filtering and
amplification, and
apply proper grounding and shielding techniques in measuring system hookups.
209