4. SIGNAL CONDITIONING
• Signal conditioning is the manipulation of an
analog signal in such a way that it meets the
requirements of the next stage for further
processing.
• The output signal from sensor of a measurement
system has to be processed to make it suitable
for the next stage of operation.
• Amplification and filtering of the signal acquired
from the sensor to make it suitable for display.
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11. FILTERING
• Filtering is the most common signal conditioning function, as usually not all the signal
frequency spectrum contains valid data. The common example is 50/60 Hz AC power
lines, present in most environments, which cause noise if amplified.
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12. AMPLIFICATION
• Signal amplification performs two important functions: increases the resolution of the input signal,
and increases its signal-to-noise ratio.
• For example, the output of an electronic temperature sensor, which is probably in the millivolts
range is probably too low for an analog to digital converter (ADC) to process directly. In this case it
is necessary to bring the voltage level up to that required by the ADC.
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13. ATTENUATION
• Attenuation, the opposite of amplification, is necessary when voltages to be digitized are
beyond the ADC range.
• This form of signal conditioning decreases the input signal amplitude so that the conditioned
signal is within ADC range.
• Attenuation is typically necessary when measuring voltages that are more than 10V.
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14. EXCITATION
• External power is required for the operation of an active sensor.
• The stability and precision of the excitation signal directly relates to the sensor
accuracy and stability.
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15. LINEARIZATION
• Linearization is necessary when sensors produce voltage signals that are not linearly related to
the physical measurement.
• Linearization is the process of interpreting the signal from the sensor and can be done either
with signal conditioning or through software.
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16. ISOLATION
• Signal isolation may be used to pass the signal from the source to the measuring device
without a physical connection.
• In some situations, it may be important to isolate the potentially expensive equipment used to
process the signal after conditioning from the sensor.
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17. SURGE PROTECTION
• A Surge protection absorbs voltage spikes to protect the next stage from damage.
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21. NEED FOR BIO-AMPLIFIER
• Generally, biological/bioelectric signals have low amplitude and low frequency.
• Therefore, to increase the amplitude level of biosignals amplifiers are designed.
• The outputs from these amplifiers are used for further analysis and they appear as ECG, EMG,
or any bioelectric waveforms. Such amplifiers are defined as Bio Amplifiers or Biomedical
Amplifiers.
• Amplifiers are an integral part of Electronic devices and modern Instrumentation for
measuring Bio-potentials. As the name indicates, Amplifiers are used to increase the signal
strength while maintaining high fidelity.
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22. REQUIREMENTS FOR BIOLOGICAL AMPLIFIERS
• The biological amplifier should have a high input impedance value. The range of value lies
between 2 MΩ and 10 MΩ depending on the applications. Higher impedance value reduces
distortion of the signal.
• When electrodes pick up biopotentials from the human body, the input circuit should be
protected.
• Every bio-amplifier should consist of isolation and protection circuits, to prevent the patients
from electrical shocks.
• Since the output of a bioelectric signal is in millivolts or microvolt range, the voltage gain value
of the amplifier should be higher than 100dB.
• Throughout the entire bandwidth range, a constant gain should be maintained.
• A bio-amplifier should have a small output impedance.
• A good bio-amplifier should be free from drift and noise.
• Common Mode Rejection Ratio (CMRR) value of amplifier should be greater than 80dB to
reduce the interference from common mode signal.
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29. DIFFERENTIAL AMPLIFIER
• These are used to amplify the
difference between the voltages
applied to its inputs. The circuits are of
two types.
• Amplifiers built using Op-Amps.
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30. INSTRUMENTATION AMPLIFIER
• Many industrial and consumer applications require the measurement and control of physical
conditions.
• For example, measurements of temperature and humidity inside a plant to accurately maintain
product quality, or precise control of the temperature furnace to produce a particular grade of
product.
• These changes in physical conditions must be converted to electrical quantities using transducers,
and then amplified. Such amplifiers, which are used to amplify signals to measure physical quantities
are commonly known as Instrumentation Amplifiers.
• The input to an instrumentation amplifier is the output signal from the transducer. A transducer is a
device which converts one form of energy into another. Most of the transducer outputs are of very
low-level signals.
• Hence, before the next stage, it is necessary to amplify the level of the signal, rejecting noise and the
interference.
• For the rejection of noise, amplifiers must have high common-mode rejection ratio.
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31. REQUIREMENTS OF A GOOD
INSTRUMENTATION AMPLIFIER
• Finite,Accurate and Stable Gain
• Easier Gain Adjustment
• High Input Impedance
• Low Output Impedance
• High CMRR
• High Slew Rate
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32. INSTRUMENTATION AMPLIFIER
• Instrumentation Amplifiers (in-amps)
are very high gain differential amplifiers
which have a high input impedance and a
single ended output.
• The instrumentation amplifier also has a
very good common mode rejection ratio,
CMRR (zero output whenV1 =V2).
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34. ADVANTAGES OF THREE OP-AMP
INSTRUMENTATION AMPLIFIER
• The gain of a three op-amp instrumentation amplifier circuit can be easily varied and
controlled by adjusting the value of Rgain without changing the circuit structure.
• The gain of the amplifier depends only on the external resistors used. Hence, it is easy to set
the gain accurately by choosing the resistor values carefully.
• The input impedance of the instrumentation amplifier is dependent on the non-inverting
amplifier circuits in the input stage.The input impedance of a non-inverting amplifier is very
high.
• The output impedance of the instrumentation amplifier is the output impedance of the
difference amplifier, which is very low.
• The CMRR of the op-amp 3 is very high and almost all of the common mode signal will be
rejected.
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