This document discusses signal conditioning in instrumentation and measurement. It defines signal conditioning as improving the quality of measurement signals by attenuating noise. Common signal conditioning techniques include filtering, amplification, attenuation, and linearization. Both analog and digital methods are used, with digital providing greater accuracy. The functions of common signal conditioning instruments like Wheatstone bridges and amplifiers are also overviewed. Finally, the document discusses data acquisition, display instruments, and recorders used in instrumentation.

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Mizan-Tepi University
College of Engineering & Technology
Department of Mechanical Engineering
COURSE NAME: INSTRUMENTATION &
MEASURMENT
CHAPTER FOUR – Signal conditioning
By: Mr. Belachew Girma

2. • Signal conditioning is concerned with improving
the quality of the reading or signal at the output of
a measurement system, and
• one particular aim is to attenuate any noise in the
measurement signal that has not been eliminated
by careful design of the measurement system.
• Signal filtering, signal amplification, signal
attenuation, signal linearization and bias removal
are done by signal processing unit.
• Signal conditioning has carried out by analogue &
digital techniques.
• Digital signal conditioning is inherently more
accurate than analogue techniques.
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3. Signal Conditioning Functions
• Amplification
– Increase the level of input signal to better suit.
– Improve the sensitivity and resolution of the measurement.
• Filtering
– Reject useless noise within certain frequency range.
– Prevent signal aliasing and distortion.
• Attenuation
– Contrary to amplification.
• Isolation
– Solve improper grounding problem of the system.
• Multiplexing
– Sequentially transmit a number of signals into single
digitiser.
• Simultaneous Sampling
– Issue of measuring more than one signals at the same time.
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4. Analogue signal filtering
• Signal filtering consists of processing a signal to
remove a certain band of frequencies within it.
• The band of frequencies removed can be either
at:
 the low-frequency end
the high-frequency end
both ends
the middle of the spectrum
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• Frequency is the rate of change with respect to
time.
• Change in a short span of time means high
frequency.
• Change over a long span of time means low
frequency.
Frequency and period are the inverse of
each other.
If a signal does not change at all, its frequency is
zero.
If a signal changes instantaneously, its frequency
is infinite.

6. • Filters to perform each of these operations are
known respectively as low-pass filters, high-
pass filters, band-pass filters and band-stop
filters (also known as notch filters).
• The range of frequencies passed by a filter is
known as the pass-band, the range not passed
is known as the stop-band, and the boundary
between the two ranges is known as the cut-off
frequency.
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Figures 4.1: Outputs from ideal filters.
Analogue filters exist in two forms, passive and
active.
Now a days, active filters are used more
commonly than passive ones.

9. Active analogue filters
• The two main difficulties noted on passive filters,
were those of obtaining resistance-less inductors
and achieving proper matching between signal
source and load through the filter sections.
• A further problem is that the inductors required
by passive filters are bulky and relatively
expensive.
• Active filters overcome all of these problems and
so they are now used more commonly than
passive filters.
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10. Signal Processing Functions
There are many possible functions in the signal-conditioning
stage. Some of the common functions are:
1. Signal amplification
• Signal amplification is carried out when the typical
signal output level of a measurement transducer is
considered to be too low.
• Amplification is carried out by an operational amplifier.
• The operational amplifier is an electronic device that has
two input terminals and one output terminal, the two
inputs being known as the inverting input and non-
inverting input respectively as shown on fig. below.
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• The raw (unprocessed) signal Vi is connected to the
inverting input through a resistor R1 and the non-
inverting input is connected to ground.
• A feedback path is provided from the output terminal
through a resistor R2 to the inverting input terminal.
• Assuming ideal operational amplifier characteristics, the
processed signal V0 at the output terminal is then related
to the voltage Vi at the input terminal by the expression:

12. 2. Signal attenuation
• One method of attenuating signals by analogue
means is to use a potentiometer connected in a
voltage-dividing circuit, as shown in Fig. below.
• For the potentiometer slider positioned a distance
of x along the resistance element of total length
L, the voltage level of the processed signal V0 is
related to the voltage level of the raw signal Vi by
the expression:
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14. 3. Differential amplification
• used to amplify the small difference that may
exist between two voltage signals VA and VB.
• These may represent, for example, the
pressures either side of an obstruction device
put in a pipe to measure the volume flow rate
of fluid flowing through it. The output voltage
V0 is given by:
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• A differential amplifier is also very useful for
removing common mode noise voltages(Vn).
• If the resistance values are chosen carefully such
that R4/R2=R3/R1, then the above equation
simplifies to:
i.e. the noise voltage Vn has been removed.

17. 4. Signal linearization
• Several types of transducer used in measuring
instruments have an output that is a non-linear function
of the measured quantity input.
• In many cases, this non-linear signal can be converted
to a linear one by special operational amplifier Signal
linearization.
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18. 5. Bias (zero drift) removal
• Sometimes, either because of the nature of the
measurement transducer itself, or as a result of
other signal conditioning operations, a bias
(zero drift) exists in the output signal. This can
be expressed mathematically for a physical
quantity x and measurement signal y as:
• Where C represents a bias in the output signal
that needs to be removed by signal processing.
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19. 6. Signal integration
• Connected in the configuration shown in Fig. below, an
operational amplifier is able to integrate the input signal
Vi such that the output signal V0 is given by:
• This circuit is used whenever there is a requirement to
integrate the output signal from a transducer.
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20. 7. Voltage follower (pre-amplifier)
• The voltage follower, also known as a pre-amplifier, is
a unity gain amplifier circuit with a short circuit in the
feedback path, as shown in Fig. below, such that:
• It has a very high input impedance and its main
application is to reduce the load on the measured
system. It also has a very low output impedance that is
very useful in some impedance-matching applications.
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21. ANALOG AND DIGITAL
• Data can be analog or digital.
• The term analog data refers to information that
is continuous; digital data refers to information
that has discrete states.
• Analog data take on continuous values.
• Digital data take on discrete values.
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Data can be analog or digital.
Analog data are continuous and take
continuous values.
Digital data have discrete states and take discrete
values.
Signals can be analog or digital.
Analog signals can have an infinite number of
values in a range; digital signals can have only a
limited
number of values.

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Analog and Digital Signals
Analog Signals
• Continuous
• Infinite range of
values
• More exact values,
but more difficult to
work with
Digital Signals
• Discrete
• Finite range of
values
• Not as exact as
analog, but easier to
work with

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Parts of an Analog Signal
Amplitude
(peak-to-peak)
Amplitude
(peak)
Period
(T)
Hz
T
1
F 
Frequency:

25. Parts of a Digital Signal
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Comparison of analog and digital signals

27. Digital signal processing
• Digital techniques achieve much greater levels of
accuracy in signal processing than equivalent
analogue methods.
• However, the time taken to process a signal
digitally is longer than that required to carry out
the same operation by analogue techniques, and
the equipment required is more expensive.
• Therefore, some care is needed in making the
correct choice between digital and analogue
methods.
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28. SIGNAL CONDITIONING
INSTRUMENTS
1. WHEATSTONE BRIDGE
2. AMPLIFIERS
3. ATTENUATORS
4. FILTERS
5. Integrators
6. Differentiators , etc.
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29. DATAACQUISITION
• Data acquisition is the process of sampling
signals that measure real world physical
conditions and converting the resulting
samples into digital numeric values that can be
manipulated by a computer.
• Data acquisition applications are usually
controlled by software programs such as
Assembly, BASIC, C, C++, C#, Fortran, Java,
LabVIEW, Lisp, Pascal, etc.
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30. DISPLAY AND RECORIDNG
INSTRUMENTS
• Display Instruments are used for the visual presentation
of information's.
1. Analog display devices (cathode-ray tubes)
• Oscilloscope tubes
•TV CRTs
2. Digital display devices
• LED (including OLED) displays
• VF (vacuum fluorescent ) displays
• LCD (liquid crystal) displays
• Nixie tube displays and PDPs (plasma display
panels)
• Electroluminescent displays (ELDs)
3. Electrical Indicating Instruments, etc. 30

31. RECORDERS
• A recorder records electrical and non-electrical
quantities as a function of time.
• The record serves the following objectives:
1. It preserves the details of measurement at a
particular time
2. It provides at a glance the overall picture of the
performance of unit
3. It provides immediate reflection on the action
taken by the operator.
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32. • Types of Recorders:
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