what is signal conditioning 2

8/10/2019 What is Signal Conditioning 2

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SIGNAL CONDITIONING:

Many applications require environment or structural measurements, such as temperature andvibration, from sensors. These sensors, in turn, require signal conditioning before a dataacquisition device can effectively and accurately measure the signal. Key signal conditioningtechnologies provide distinct enhancements to both the performance and accuracy of dataacquisition systems.

Signal conditioning is basically the process of making modification in the original

signal. This modification may be carrying different types of purposes along with it

like making the signal usable at the oncoming stages of the particular system,

changing it from one form to another one so that required processing may be done

over it

The measurand, which is a physical quantity as is detected by the first stage of the

instrumentation or measurement system. The first stage, with which we have become

familiar is Detector TransducerStage. The quantity is detected and is transduced into an

electrical form in most of the cases. The output of the first stage has to be modified before it

becomes usable and satisfactory to drive the signal presentation stage which is the third and

the last stage of a measurement system. The last stage of the measurement system mayconsist of indicating, recording, displaying, data processing elements or may consist of

control elements.

Measurement of dynamic physical quantities requires faithful representation of their analog

or digital output obtained from the intermediate stage I;esignal conditioningstage and this

places a severe strain on the signal conditioning equipment. The signal conditioning

equipment may be required to do linear processes like amplification, attenuation, integration,

differentiation, addition, and subtraction. They are also required to do non-linear processes

like modulation, demodulation, sampling, filtering, clipping and clamping, squaring,

linearisation or multiplication by another function etc.

Signal condition or also called data acquisition equipment in many a situation is an

excitation and amplification system for passive transducers. It may be an amplifier

system for active transducer. In both the applications the transducer output is brought

up to a sufficient level to make it useful for conversion, process indication and also

for recording the result for future use. Excitation used for passive transducers because

of the reason that these transducers do not make the voltage and current of their own.

So this is the reason that the transducers like stain gauss, potentiometer, resistance

thermometer, inductive transducer, capacitive transducer requires excitation from

some external mean.


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There are also many active transducers like technogenerators, thermocouple, inductive

pick up and piezo-electric crystals, on the other hand, do not requires an external

source of excitation since they produce their own electrical output on the account ofapplication of the physical quantities. But these signals usually have low voltage level

and hence need amplification to make it possible to feed to oncoming stages of the

system so that required result may be obtained. The excitation sources may be an

alternative or direct (D.C.) voltage source. The D.C. system is comparatively simpler

and this can also shown with the help of the following figure which is actually a block

diagram of the functioning which actually occurs.

Transducers:

Transducers are devices that convert one type of physical phenomenon, such as temperature,strain, pressure, or light into another. The most common transducers convert physical

quantities to electrical quantities, such as voltage or resistance. Transducer characteristicsdefine many of the signal conditioning requirements of your measurement system. Table 1summarizes the basic characteristics and conditioning requirements of some commontransducers

.


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Sensor Electrical Characteristics Signal Conditioning Requirement

Thermocouple Low-voltage outputLow sensitivityNonlinear output

Reference temperature sensor (forcold-junction compensation)High amplification

Linearization

RTD Low resistance (100 ohms typical)Low sensitivityNonlinear output

Current excitationFour-wire/three-wire configurationLinearization

Strain gauge Low resistance deviceLow sensitivityNonlinear output

Voltage or current excitationHigh amplificationBridge completionLinearization

Shunt calibration

Current outputdevice

Current loop output (4 -- 20 mAtypical)

Precision resistor

Thermistor Resistive deviceHigh resistance and sensitivityVery nonlinear output

Current excitation or voltageexcitation with reference resistorLinearization

ActiveAccelerometers

High-level voltage or currentoutputLinear output

Power sourceModerate amplification

AC LinearVariableDifferentialTransformer(LVDT)

AC voltage output AC excitationDemodulationLinearization

The Analog Front End:

Most analog-to-digital systems include an analog front end that serves as the interface

between the sensor/input analog signals and the ADCs. Incoming signals are very rarely in a

state where they can be sent directly to the ADC and usually require some sort of

transformation or adaptation to ensure that they will be digitized under optimal conditions.

The main elements commonly found in analog front ends are illustrated in the figure below.


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A typical configuration and is only intended to present the various building blocks that are

usually found in acquisition system analog front-ends. doesnt An actual implementation is

very application dependent and will consist of a multi-stage assembly-line configuration,

where different instances of these blocks will be combined to provide an optimal analog

processing chain between the input signals and the ADCs.

The location of the analog front end is also very application specific, but will necessarily be

one of three possible configurations: near or integrated with the sensor; integrated in a

dedicated unit located between the sensor and the ADC; and near or integrated with the

ADC. The ideal location for the front end is normally determined by a series of electrical,

mechanical and economic considerations, which are outside the scope of this discussion.

Well leave that subject open for other discussions in the future.

SIGNAL CONDITIONING TECHNIQUES:

FILTERING:

Filters play a vital role in data acquisition systems to remove selected frequencies

from an incoming signal and minimize artifacts (i.e. baseline wander, mains

,interference and noise). Analog/hardware filters are used to filter the incoming,

continuous signal before it is sampled by the analog to digital converter (ADC). These

filters are included in ADInstruments front-ends (Bio Amps, Bridge Amps etc) and in

some of the PowerLab units themselves. ADInstruments front-ends initially amplify

the signal to a level suitable for filtering. The analog filters are then used to remove

unwanted frequencies, following which further amplification is performed before

digitization. Filtering the signal prior to full amplification is essential for biopotential

measurements to improve the signal to noise ratio. The analog/hardware filters

included in the S, SP and 30 series PowerLabs provide additional filtering to remove

high frequency components (anti-aliasing low-pass filters) before the signal is

digitized. Additional Digital/Software filters are included in Chart and filter the data

after it has been sampled and recorded by the PowerLab.

Digital filters are used post data acquisition and are advantageous because:

It is possible to design digital filters that are impractical to make in analog form

They are stable over time and provide consistent, reproducible signal filtering

In Chart, they can be applied post data acquisition while the raw data is retained


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However, a disadvantage of post-acquisition, digital filtering is that unless

analog/hardware filters have also been used prior to digitization, any noise or

baseline offset present in the signal has also been amplified and will have a negative

effect on signal resolution.

Filters reject unwanted noise within a certain frequency range. Oftentimes, lowpass filters

are used to block out high-frequency noise in electrical measurements, such as 60 Hz power.

Another common use for filtering is to prevent aliasing from high-frequency signals. This

can be done by using an antialiasing filter to attenuate signals above the Nyquist frequency.

Low-Pass Filter:

A low-pass filter allows signal frequencies below the low cut-off frequency to pass

and stops frequencies above the cut-off frequency. It is commonly used to help reduce

environmental noise and provide a smoother signal.

A simple way to understand how a filter works is to plot signal frequency against

signal gain When a signal is unfiltered, it is recorded at a gain of 1, that is, the full

signal is being recorded. However, when a signal is filtered, the gain (amount of

signal is reduced)


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1). The frequency at which the gain starts to decrease by a reasonable amount is the

cut-off (corner) frequency (fc).

Ideally, low-pass filters would provide a gain of 1 below the cut-off frequency and a

gain of zero above this cut-off value (i.e. no signal is recorded). However, filters areimperfect and some level of the signal is always recorded. This reduction in signal

gain after the cut-off frequency is commonly referred to as signal attenuation and is

commonly presented in decibel (dB) units. While signal attenuation is progressive

rather than an ideal all-or-none process, all low-pass filters have a frequency (fa;

Figure 1) above which the gain is very small (the signal is virtually non-existent).

Note: Decibels are not units of measurement in the conventional sense (ie meter or

joule) but represent a ratio, thereby describing how much bigger or smaller one thing

is compared to another.

All signal frequencies below the cut-off frequency are referred to as the passband. All

signal frequencies above the cut-off frequency are referred to as the stopband. The

region between the pass- and stop-bands is referred to as the transition band or

transition width. This width (in Hz) depends on how sharply the filter response drops

from the pass band to the stop band. Related to this is the roll-off rate, which, for low-

pass filters is the rate at which the signal gain decreases when the signal is above the

cut-off frequency. The narrower the transition band, the steeper the roll-off.


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ISOLATION:

Voltage, current, temperature, pressure, strain, and flow measurements are an integral part ofindustrial and process control applications. Often these applications involve environments

with hazardous voltages, transient signals, common-mode voltages, and fluctuating ground

potentials capable of damaging measurement systems and ruining measurement accuracy. Toovercome these challenges, measurement systems designed for industrial applications makeuse of electrical isolation. This white paper focuses on isolation for analog measurements,provides answers to common isolation questions, and includes information on differentisolation implementation..

Understanding Isolation:

Isolation electrically separates the sensor signals, which can be exposed to hazardous

voltages1, from the measurement systems low-voltage backplane. Isolation offers many

benefits including:

Protection for expensive equipment, the user, and data from transient voltages

Improved noise immunity Ground loop removal

Increased common-mode voltage rejection

Isolated measurement systems provide separate ground planes for the analog front end andthe system backplane to separate the sensor measurements from the rest of the system. Theground connection of the isolated front end is a floating pin that can operate at a differentpotential than the earth ground. Figure 1 represents an analog voltage measurement device.Any common-mode voltage that exists between the sensor ground and the measurementsystem ground is rejected. This prevents ground loops from forming and removes any noiseon the sensor lines.

Need for Isolation:

Consider isolation for measurement systems that involve any of the following:

Close vicinity to hazardous voltages

Industrial environments with possibility of transient voltages

Environments with common-mode voltage or fluctuating ground potentials

Electrically noisy environments such as those with industrial motors

Transient-sensitive applications where it is imperative to prevent voltage spikes from beingtransmitted through the measurement system


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Industrial measurement, process control, and automotive test are examples of applicationswhere common-mode voltages, high voltage transients, and electrical noise are common.Measurement equipment with isolation can offer reliable measurements in these harshenvironments. For medical equipment in direct contact with patients, isolation is useful inpreventing power line transients from being transmitted through the equipment.

Based on your voltage and data rate requirements, you have several options for makingisolated measurements. You can use plug-in boards for laptops, desktop PCs, industrial PCs,PXI, panel PCs, and CompactPCI with the option of built-in isolation or external signalconditioning. You also can make isolated measurements using programmable automationcontrollers (PACs) and measurement systems for USB, Ethernet and wireless.

Methods of Implementing Isolation:

Isolation requires signals to be transmitted across an isolation barrier without any directelectrical contact. Light-emitting diodes (LEDs), capacitors, and inductors are threecommonly available components that allow electrical signal transmission without any directcontact. The principles on which these devices are based form the core of the three mostcommon technologies for isolationoptical, capacitive, and inductive coupling.

Optical Isolation:

LEDs produce light when a voltage is applied across them. Optical isolation uses an LEDalong with a photodetector device to transmit signals across an isolation barrier using light asthe method of data translation. A photodetector receives the light transmitted by the LED andconverts it back to the original signal.


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Optical isolation is one of the most commonly used methods for isolation. One benefit ofusing optical isolation is its immunity to electrical and magnetic noise. Some of thedisadvantages include transmission speed, which is restricted by the LED switching speed,high-power dissipation, and LED wear.

Capacitive Isolation

Capacitive isolation is based on an electric field that changes with the level of charge on a

capacitor plate. This charge is detected across an isolation barrier and is proportional to thelevel of the measured signal.

One advantage of capacitive isolation is its immunity to magnetic noise. Compared to opticalisolation, capacitive isolation can support faster data transmission rates because there are noLEDs that need to be switched. Because capacitive coupling involves the use of electricfields for data transmission, it can be susceptible to interference from external electric fields.

Inductive Coupling Isolation:

In the early 1800s, Hans Oersted, a Danish physicist, discovered that current through a coilof wire produces a magnetic field. It was later discovered that current can be induced in a

second coil by placing it in close vicinity of the changing magnetic field from the first coil.The voltage and current induced in the second coil depend on the rate of current changethrough the first. This principle is called mutual induction and forms the basis of inductiveisolation.


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Inductive isolation uses a pair of coils separated by a layer of insulation. Insulation preventsany physical signal transmission. Signals can be transmitted by varying current flowingthrough one of the coils, which causes a similar current to be induced in the second coilacross the insulation barrier. Inductive isolation can provide high-speed transmission similarto capacitive techniques. Because inductive coupling involves the use of magnetic fields fordata transmission, it can be susceptible to interference from external magnetic fields.

Analog Isolation and Digital Isolation

Many of the commercial off-the-shelf (COTS) components available today incorporate oneof the above technologies to provide isolation. For analog I/O channels, you can implementisolation either in the analog section of the device before the analog-to-digital converter(ADC) has digitized the signal (analog isolation) or after the ADC has digitized the signal(digital isolation).

Figure 6a. Analog Isolation

Analog Isolation:

The isolation amplifier is generally used to provide isolation in the analog front end of data

acquisition devices. ISO Amp in Figure 6a represents an isolation amplifier, which, inmost circuits, is one of the first components of the analog circuitry. The analog signal from asensor is passed to the isolation amplifier, which provides isolation and passes the signal tothe analog-to-digital conversion circuitry. Figure 7 represents the general layout of an

isolation amplifier.


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In an ideal isolation amplifier, the analog output signal is the same as the analog input signal.

The section labeled isolationuses one of the techniques discussed in the previous section(optical, capacitive, or inductive coupling) to pass the signal across the isolation barrier. The

modulator circuit prepares the signal for the isolation circuitry. For optical methods, youneed to digitize or translate this signal into varying light intensities. Because you performanalog isolation before the signal is digitized, it is the best method to apply when designingexternal signal conditioning for use with existing non-isolated data acquisition devices. Inthis case, the data acquisition device performs the analog-to-digital conversion and theexternal circuitry provides isolation. With the data acquisition device and external signalconditioning combination, measurement system vendors can develop general-purpose dataacquisition devices and sensor-specific signal conditioning. Figure 8 shows analog isolationbeing implemented with flexible signal conditioning that uses isolation amplifiers. Anotherbenefit to isolation in the analog front end is protection for the ADC and other analog

circuitry from voltage spikes.

Digital Isolation


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ADCs are one of the key components of any analog input data acquisition device.For best performance, the input signal to the ADC should be as close to the originalanalog signal as possible. Analog isolation can add errors such as gain, nonlinearity,and offset before the signal reaches the ADC. Placing the ADC closer to the signalsource can lead to better performance. Analog isolation components are also costlyand can suffer from long settling times. Despite better digital isolation performance,one of the reasons for using analog isolation in the past was to provide protection forthe expensive ADCs. Because ADC prices have significantly declined, measurementequipment vendors are choosing to trade ADC protection for the better performanceand lower cost offered by digital isolators.

Compared to isolation amplifiers, digital isolation components are lower in cost andoffer higher data transfer speeds. Digital isolation techniques also give analogdesigners more flexibility to choose components and develop optimal analog frontends for measurement devices. Products with digital isolation use current- andvoltage-limiting circuits to provide ADC protection. Digital isolation componentsfollow the same fundamental principles of optical, capacitive, and inductive couplingthat form the basis of analog isolation.

Cold-Junction Compensation:

Cold-junction compensation (CJC) is a technology required for accurate

thermocouple measurements. Thermocouples measure temperature as the

difference in voltage between two dissimilar metals. Based on this concept, another

voltage is generated at the connection between the thermocouple and terminal of

your data acquisition device. CJC improves your measurement accuracy by

providing the temperature at this junction and applying the appropriate correction.

The terms hot junctionand cold junction,as applied to thermocouple devices, are

mostly historical. You don't need to have any junctionsto get thermocouple effects.


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If you heat one end of a metal conductor and hold the other end at a constantreference temperature, two important things occur.

1. Heat flow.There is a thermal gradient, so heat flows from the hot end to the coldend. With small-gage thermocouple wire, very little thermal energy actually reaches

the cold end, and the thermal gradient is typically not constant along the wiresbecause of heat loss.

2. Seebeck effect.Energetic electrons at the hot end diffuse toward the cold end,pushing less energetic electrons along with them, resulting in a higher staticpotential at the hot end relative to the cold end. The larger the temperature gradientthe larger the potential difference. (There are additional contributing effects whendissimilar materials are joined.)

In practice, it is difficult to measure the Seebeck effect directly. When you attachmeasurement probes, there is a thermal difference across the probe leads,producing additional thermocouple effects that interfere with the measurements.

Classical thermocouple loop configuration

To make the thermal effects measurable, two different metal conductors are used.They must be chemically, electrically, and physically compatible. They producedifferent electric potentials when subjected to the same thermal gradient.

In the classical configuration, the dissimilar thermocouple wires are welded togetherat the measurement end (hot junction), and again at the reference end (coldjunction), forming a loop. The hot junction assures that the potential at that pointmatches in the two metals. Immersing the reference-end junction in an ice-waterslurry assures that the temperature gradients are the same across both materials.The ice-water slurry establishes a reference temperature at 0 degrees C.

Welding the thermocouple wires at the cold junction also equalizes the potentialsthere. To make the potential difference observable again, it is necessary to breakthe loop. Pick a location in one of the thermocouple wires where the temperaturematches the temperature of the measurement leads. Break the loop there, andattach matching leads to the two sides of the gap to measure the potential.


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By maintaining uniform temperatures where the leads connect, thermal gradientsare unaffected.

By avoiding thermal gradients across lead wires, stray thermocouple effects are keptsmall.

By matching the leads well, any residual effects cancel out of differentialmeasurements.

Cold junction in practice

Maintaining an ice water slurry and actual cold junction is rarely feasible. Typically,the cold junction is omitted, and the potential is measured directly across the twoterminal ends of the thermocouple wires at ambient temperature. For historicalreasons, we speak of the terminal ends of the thermocouple wires as the cold

junction,despite the fact that there is no longer an intentional junction. (For thesame historical reasons, we refer to the measurement junction of the thermocoupleas the hot junctioneven if it is used to measure below-zero temperatures.) Themeasured potential indicates the temperature difference between the hot junctionpoint and the unknown cold junction terminals. To complete the temperaturemeasurement, you must determine the terminal temperature in some manner.

Cold Junction Compensation

There are two commonly used approaches.

1. Simulate the potential effects that would result for a thermocouple wire pair betweenthe terminals, at their measured temperature, and another junction at a referencetemperature of 0 degrees. Measure the potential across the thermocouple wire pair

in series with the simulated potential. Apply the linearizing curve to the sum, thusobtaining an estimated absolute temperature directly. This is known ascold junctioncompensation. Usually, the simulation is done electronically with specializedintegrated circuit devices.


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This approach makes two approximation errors, one for estimating the cold junctiontemperature, and one for approximating the effects on junction potential. Beyondwhat is already built into the electronic simulation, calibration is tricky and probablylimited to offset adjustment.

2. Independently measure the temperature of the cold junction. Measure thethermocouple potential and apply conversion curves to determine the temperaturedifference across the thermocouple. Then add the known cold junction temperatureto the measured temperature difference to determine the absolute temperaturemeasurement.

This approach uses one less estimate, but it still depends on accuratemeasurements of the cold junction temperature

Excitation:

Excitation is required for many types of transducers. For example, strain gages,accelerometers thermistors, and resistance temperature detectors (RTDs) require external

voltage or current excitation. RTD and thermistor measurements are usually made with acurrent source that converts the variation in resistance to a measurable voltage.Accelerometers often have an integrated amplifier, which requires a current excitationprovided by the measurement device. Strain gages, which are very-low-resistance devices,typically are used in a Wheatstone bridge configuration with a voltage excitation source

Input transducers, orsensorsare classified as either active or passive.Passivesensors, such

as thermocouples or photodiodes (in the voltage-output mode) are two-port devices thattransform physical energy to electrical energy directly, generating output signals without the

need for an excitation source.Activesensors (like active circuits in general) require anexternal source of excitation. Examples can be found in the class of resistor-based sensors,such as thermistors, RTDs (resistance-temperature detectors), and strain gages; they require a

current or voltage for excitation in order to produce an electrical output.

This article will consider a variety of excitation methods that can be used in activesensor/transducer applications and will show some typical circuits. The discussion includes

the benefits and shortcomings of ac and dc excitation techniques using current and voltage.Accurate measurement of low-level analog signals with a data-acquisition system generallyrequires more than simply wiring the output of the transducer to the signal conditioningcircuitry and then to the analog to digital converter. To maintain high-resolution andaccuracy within the measurement system, the designer must exercise care in selecting theexcitation source for the transducerand in the field-wiring scheme used in conveying thelow-level analog signal from the transducer to the A/D converter. Figure 1 shows a

generalized block diagram of a transducer-based data acquisition system. The integrity of the

data acquired in these systems depends on all parts of the analog signal path shown here.


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For a given excitation source, the system designer is faced with the challenge of measuringthe output signal and dealing with the issues that may arise. For example, wiring resistanceand noise pickup are among the biggest problems associated with sensor based applications.A variety of measurement techniques are available for employment in quest of optimumperformance from the measurement system. Principal choices include ratiometric vs. non-ratiometric operation, and 2-wire vs. 3-, and 4-wire Kelvin force/sense connections.

Excitation Techniques:

Active transducers can be excited using a controlled current or voltage. The choice between

voltage and current excitation is generally at the discretion of the designer. In data-acquisition systems, it's not uncommon to see constant-voltage excitation used for strain andpressure sensors, while constant current excitation is used to excite resistive sensors such asRTDs or thermistors. In noisy industrial environments, current excitation is generallypreferable due to its better noise immunity.

AC or dc excitation sources can be used in transducer applications; each offers advantages

and disadvantages. The advantages associated with dc excitation include simplicity ofimplementation and low cost. The downside of dc excitation includes the difficulty of

separating the actual signal from unwanted dc errors due to offsets and parasitic inducedthermocouple effects. DC offsets are not fixed; they vary unpredictably due to temperaturedrift and both thermal and 1/f noise sources.

Amplification:

Amplifiers increase voltage level to better match the analog-to-digital converter (ADC)range, thus increasing the measurement resolution and sensitivity. In addition, using externalsignal conditioners located closer to the signal source, or transducer, improves the

measurement signal-to-noise ratio by magnifying the voltage level before it is affected byenvironmental noise

Amplification is the set of techniques used to boost a signal's strength. Figure 2shows acombination of an idealized transducer and an idealized amplifier. The key features of thetransducer model are an open-circuit voltage (VOCT) and an output impedance (rOT). Theamplifier has an input impedance rIN, an output impedance rOA, and an open-circuit outputvoltage defined as VOCA = AVVIN, where AV is the amplifier's gain.


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Maintaining Accurate Gain :

While the overall goal is to increase the amplitude of the transducer's output signal, there are

a number of secondary goals that must be considered when selecting or designing an

amplifier. One of the most important of these in many sensor systems is to maintain accurategain. In the system of Figure 2, there are two fundamental ways you can achieve this.

The first is to simply make the amplifier's input impedance much higher than the transducer's

output impedance. The signal seen at the amplifier's input will be VOCT [rIN/(rIN+rOT)],which is about equal to VOCT when rIN >>rOT. For example, with transducer outputimpedances less than a few megohms, a simple op amp amplifier circuit such as the one canoften be used. When implemented with a suitable FET-input op amp, this circuit can providein excess of 10

10 of input impedance at DC. Using a very high input impedance amplifier

is often an adequate and simple solution to many interface problems.

Special Cases:

In some cases, especially those involving high-frequency signals or very small signals, thehigh-input impedance solution may not be adequate. At high frequencies, an amplifier's input

impedance may be dominated by a reactive component. For example, a FET-input amplifierthat provides 1012 input impedance at DC may have a 1 pF input capacitance, whichappears as roughly 160 k at 1 MHz. So much for the benefit of high DC impedance.


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LINEARISATION AND CALIBRATION PROCESS:

LINEARISATION:

Linearization is necessary when sensors produce voltage signals that are not linearly relatedto 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. Thermocouplesare the classic example of a sensor that requires linearization.

Many sensors are used m automated systems m industrial plants They need to be calibratedwhen first installed and they need recalibration as they drift with age and process conditions(such as temperature and pressure) After some change is made to a new instrument or when

old sensors are being replaced with new sensors, a recalibration is needed m order tocompare the sensor signal with previous measurements of the reference data base In practice,

the sensor cahbration is performed by putting the sensor m a controlled environment .

LINEARISATION AND CALIBRATION PROCESS:

A certain number of measurements need to be taken m order to determine and

correct a sensors nonlmeanty The number of measurements necessary to re-

duce the heavy error depends on the linearising calibration method used and

to reduce the costs of calibration it is important to minimize the number of mea

surements Costs refer to the expense of processing power and time This is

an important criterion m the selection of an appropriate linearising calibration

method for sensor calibration

Sensor characteristic linearization:


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Bridge Completion

Bridge completion is required for quarter- and half-bridge sensors to comprise a four

resistor Wheatstone bridge. Strain gage signal conditioners typically provide half-

bridge completion networks consisting of high-precision reference resistors. The

completion resistors provide a fixed reference for detecting small voltage changes

across the active resistor(s).

Amplification

Attenuation

Isolation

Filtering

Excitation

Linearization

CJC

BridgeCompletion

Thermocouple

Thermistor

RTD

StrainGage

Load,Pressure,Torque(mV/V)

Load,Pressure,Torque (5V, 10 V,4-20 mA)

Accelerometer

Microphone

ProximityProbe

LVDT/RVDT

HighVoltage

Thus the output of the signal conditioning circuit is given to the DAS.

what is signal conditioning 2

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