Signal conditioning
Encyclopedia
In electronics, signal conditioning means manipulating an analog signal
in such a way that it meets the requirements of the next stage for further processing. Most common use is in analog-to-digital converter
s.
In control engineering
applications, it is common to have a sensing stage (which consists of a sensor
), a signal conditioning stage (where usually amplification of the signal is done) and a processing stage (normally carried out by an ADC
and a micro-controller). Operational amplifiers (op-amps) are commonly employed to carry out the amplification of the signal in the signal conditioning stage.
and current, AC voltage
and current, frequency
and electric charge
. Sensor inputs can be accelerometer
, thermocouple
, thermistor
, resistance thermometer
, strain gauge
or bridge, and LVDT or RVDT. Specialized inputs include encoder, counter or tachometer
, timer or clock, relay or switch, and other specialized inputs. Outputs for signal conditioning equipment can be voltage, current, frequency, timer or counter, relay, resistance or potentiometer, and other specialized outputs.
, filtering
, converting, range matching, isolation and any other processes required to make sensor output suitable for processing after conditioning.
is the most common signal conditioning function, as usually not all the signal frequency spectrum contains valid data. The common example are 60Hz AC power lines, present in most environments, which will produce noise if amplified.
performs two important functions: increases the resolution of the inputed 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
.
Commonly used amplifiers on signal conditioning include Sample and hold
amplifiers, Peak Detectors, Log amplifiers, Antilog amplifiers, Instrumentation amplifiers or programmable gain amplifiers.
Magnetic or optic isolation
can be used. Magnetic isolation transforms the signal from voltage to a magnetic field, allowing the signal to be transmitted without a physical connection (for example, using a transformer). Optic isolation takes an electronic signal and modulates it to a signal coded by light transmission (optical encoding), which is then used for input for the next stage of processing.
Alog-to-digital conversion so they can be read by computerized devices. Other uses include preprocessing signals in order to reduce computing time, converting ranged data to boolean values, for example when knowing when a sensor has reached certain value.
Types of devices that use signal conditioning include signal filters, instrument amplifier
s, sample-and-hold amplifiers, isolation amplifier
s, signal isolators, multiplexer
s, bridge conditioners, analog-to-digital converter
s, digital-to-analog converter
s, frequency converters or translators, voltage converter
s or inverters
, pplications
It is primarily utilized for [[data acquisition]], in which sensor signals must be normalized and filtered to levels suitable for anafrequency-to-voltage converters, voltage-to-frequency converters, current-to-voltage converter
s, current loop converters, and charge converters.
Analog signal
An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
in such a way that it meets the requirements of the next stage for further processing. Most common use is in analog-to-digital converter
Analog-to-digital converter
An analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...
s.
In control engineering
Control engineering
Control engineering or Control systems engineering is the engineering discipline that applies control theory to design systems with predictable behaviors...
applications, it is common to have a sensing stage (which consists of a sensor
Sensor
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...
), a signal conditioning stage (where usually amplification of the signal is done) and a processing stage (normally carried out by an ADC
Analog-to-digital converter
An analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...
and a micro-controller). Operational amplifiers (op-amps) are commonly employed to carry out the amplification of the signal in the signal conditioning stage.
Inputs
Signal inputs accepted by signal conditioners include DC voltageDirect current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
and current, AC voltage
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
and current, frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
and electric charge
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
. Sensor inputs can be accelerometer
Accelerometer
An accelerometer is a device that measures proper acceleration, also called the four-acceleration. This is not necessarily the same as the coordinate acceleration , but is rather the type of acceleration associated with the phenomenon of weight experienced by a test mass that resides in the frame...
, thermocouple
Thermocouple
A thermocouple is a device consisting of two different conductors that produce a voltage proportional to a temperature difference between either end of the pair of conductors. Thermocouples are a widely used type of temperature sensor for measurement and control and can also be used to convert a...
, thermistor
Thermistor
A thermistor is a type of resistor whose resistance varies significantly with temperature, more so than in standard resistors. The word is a portmanteau of thermal and resistor...
, resistance thermometer
Resistance thermometer
Resistance thermometers, also called resistance temperature detectors or resistive thermal devices , are sensors used to measure temperature by correlating the resistance of the RTD element with temperature. Most RTD elements consist of a length of fine coiled wire wrapped around a ceramic or glass...
, strain gauge
Strain gauge
A strain gauge is a device used to measure the strain of an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable...
or bridge, and LVDT or RVDT. Specialized inputs include encoder, counter or tachometer
Tachometer
A tachometer is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute on a calibrated analogue dial, but digital displays are increasingly common...
, timer or clock, relay or switch, and other specialized inputs. Outputs for signal conditioning equipment can be voltage, current, frequency, timer or counter, relay, resistance or potentiometer, and other specialized outputs.
Signal conditioning processes
Signal conditioning can include amplificationAmplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
, filtering
Filter (signal processing)
In signal processing, a filter is a device or process that removes from a signal some unwanted component or feature. Filtering is a class of signal processing, the defining feature of filters being the complete or partial suppression of some aspect of the signal...
, converting, range matching, isolation and any other processes required to make sensor output suitable for processing after conditioning.
Filtering
FilteringElectronic filter
Electronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal, to enhance wanted ones, or both...
is the most common signal conditioning function, as usually not all the signal frequency spectrum contains valid data. The common example are 60Hz AC power lines, present in most environments, which will produce noise if amplified.
Amplifying
Signal amplificationAmplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
performs two important functions: increases the resolution of the inputed 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
Analog-to-digital converter
An analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...
(ADC) to process directly. In this case it is necessary to bring the voltage level up to that required by the ADC
Analog-to-digital converter
An analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...
.
Commonly used amplifiers on signal conditioning include Sample and hold
Sample and hold
In electronics, a sample and hold circuit is an analog device that samples the voltage of a continuously varying analog signal and holds its value at a constant level for a specified minimal period of time. Sample and hold circuits and related peak detectors are the elementary analog memory...
amplifiers, Peak Detectors, Log amplifiers, Antilog amplifiers, Instrumentation amplifiers or programmable gain amplifiers.
Isolation
Signal isolation must be used in order to pass the signal from the source to the measurement device without a physical connection: it is often used to isolate possible sources of signal perturbations. Also notable is that's it is important to isolate the potentially expensive equipment used to process the signal after conditioning from the sensor.Magnetic or optic isolation
Optical isolator
An optical isolator, or optical diode, is an optical component which allows the transmission of light in only one direction. It is typically used to prevent unwanted feedback into an optical oscillator, such as a laser cavity...
can be used. Magnetic isolation transforms the signal from voltage to a magnetic field, allowing the signal to be transmitted without a physical connection (for example, using a transformer). Optic isolation takes an electronic signal and modulates it to a signal coded by light transmission (optical encoding), which is then used for input for the next stage of processing.
Alog-to-digital conversion so they can be read by computerized devices. Other uses include preprocessing signals in order to reduce computing time, converting ranged data to boolean values, for example when knowing when a sensor has reached certain value.
Types of devices that use signal conditioning include signal filters, instrument amplifier
Instrument amplifier
An instrument amplifier is an electronic amplifier that converts the often barely audible or purely electronic signal from musical instruments such as an electric guitar, an electric bass, or an electric keyboard into an electronic signal capable of driving a loudspeaker that can be heard by the...
s, sample-and-hold amplifiers, isolation amplifier
Isolation amplifier
Isolation amplifiers provide electrical isolation and an electrical safety barrier. They protect data acquisition components from common mode voltages, which are potential differences between instrument ground and signal ground...
s, signal isolators, multiplexer
Multiplexer
In electronics, a multiplexer is a device that selects one of several analog or digital input signals and forwards the selected input into a single line. A multiplexer of 2n inputs has n select lines, which are used to select which input line to send to the output...
s, bridge conditioners, analog-to-digital converter
Analog-to-digital converter
An analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...
s, digital-to-analog converter
Digital-to-analog converter
In electronics, a digital-to-analog converter is a device that converts a digital code to an analog signal . An analog-to-digital converter performs the reverse operation...
s, frequency converters or translators, voltage converter
Voltage converter
A voltage converter changes the voltage of an electrical power source. It may be combined with other components to create a power supply.-AC and DC:...
s or inverters
Inverter (electrical)
An inverter is an electrical device that converts direct current to alternating current ; the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits....
, pplications
It is primarily utilized for [[data acquisition]], in which sensor signals must be normalized and filtered to levels suitable for anafrequency-to-voltage converters, voltage-to-frequency converters, current-to-voltage converter
Current-to-voltage converter
In electronics, a transimpedance amplifier is an amplifier that converts current to voltage. Its input ideally has zero impedance, and the input signal is a current...
s, current loop converters, and charge converters.