How to Select Data Acquisition Systems and Instruments
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Data acquisition systems and instruments are either the combination of a number of data acquisition components that make up a complete system or a self-contained instrument. They are used to collect, digitize, and process multiple sensor or signal inputs for the purpose of monitoring, analyzing, and/or controlling systems and processes. Data acquisition systems and instruments are configured in a wide variety of instrumentation and modular systems. Applications include manufacturing testing of all types of technical products, safety, environmental, certification, and research projects.
System Components
Data acquisition systems are comprised of front-end devices, a central processing unit, and back-end devices. Front end devices receive inputs and provide filtering, amplification, converting, and / or other processes required to make the signal suitable for data acquisition. A central processing unit receives and processes the digitized inputs. The back-end is a feedback loop comprised of conditioned outputs used to trigger alarms, provide control signals or transmit the acquired data.
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Components used in a data acquisition system include data acquisition computer boards, data input modules, data acquisition output modules, data acquisition I/O devices, signal conditioners, and signal converters.
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Data acquisition computer boards are self-contained printed circuit boards (PCBs) that plug into backplanes and motherboards, or interface directly with computer buses. They receive multiple electrical or electronic inputs from devices such as sensors and translate analog data into a digital format that computers can process. |
Image Credit: Measurement Computing |
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Data input modules receive signals from devices such as sensors and often provide voltage and current excitation along with signal conditioning. They are a front end device that interfaces with computer boards, systems, instruments, or recorders. |
Image Credit: Endress+Hauser, Inc. |
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Data output modules transfer amplified, conditioned, or digitized signals to processing systems or devices. They are a backend device and the signal is a conditioned output from a computer board, system, instrument, or recorder. |
Image Credit: D-TACQ Solutions |
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I/O modules and instruments have both input and output functionality. Digital or discrete I/O modules include on-off signals used in communication, user interface, or control. |
Image Credit: Acromag, Inc. |
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Signal conditioning is a set of operations performed on a signal that makes it suitable for interfacing with other devices or systems. Signal conditioners are the actual devices that perform this operation. These devices have an input and an output. Normally the input is a sensor that measures a variable, not necessarily and electrical signal. |
Image Credit: Dataforth Corporation |
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A signal is an electric current or electromagnetic field used to convey data from one place to another. Signal converters are electronic devices that receive one type of signal and output another type of signal. They can be found in many industrial and commercial applications. |
Image Credit: DEWETRON, Inc. |
Device Function
The function of the device is to monitor, analyze or control systems and processes.
Monitor
Data acquisition systems and instruments used to monitor processes and systems have the ability to record data points over a timed interval. They are customized for a particular application and may require specific modules in order to accommodate the type or number of inputs used. They may be equipped with on-board memory, removable storage, or may interface with a computer, used to process, store, and visualize the data. They may also be equipped with a switched output used to trigger an alarm or activate a switch when a pre-set condition is met or exceeded.
Monitoring with a virtual chart recorder.
Image Credit: Newport Electronics, Inc.
Analyze
Data acquisition systems and instruments may be used for data analysis. Data points or real-time data can be fed into a system that reduces or compiles data in order to generate useful information. Fourier transforms are used to reduce a signal with respect to time into a series of sinusoidal terms. Application software is commonly used for signal processing and measurement functions.
Fast fourier transforms (FFT). Image Credit: The Register
Control
Data acquisition systems and instruments can be used to control processes and systems. The central processing unit receives a feedback signal and produces a switched output or analog control signal that is used to control devices in a system or process. Common applications include motion control, industrial automation, web processing, and other industrial operations. Supervisory control and data acquisition (SCADA) systems are large-scale, industrial control and measurement systems that consist of a central host, one or more remote units, a communications network, and specialized software. More detailed information about SCADA is available in GlobalSpec's Supervisory Control and Data Acquisition Systems (SCADA) Selection Guide.
Water Treatment - SCADA- Plant-IQ
Video Credit: mmassaNY
Form Factor
Common form factors for data acquisition systems and instruments include circuit board, panel or chassis mount, modular bay or slot system, rack mount, DIN rail, and stand-alone.
- Printed circuit boards (PCBs) attach to enclosures or plug into computer backplanes.
- Panel or chassis mounts are used to install the device in cabinets, enclosures, or panels with bolts.
- Modular style units include stackable units that dock in bays, slots, or boxes.
- Rack units that fit inside a standard 19” telecommunications rack.
- Devices can be designed for mount on a Standard Deutsches Institute for Normung (DIN) rail, which is a German standard.
- Benchtop or freestanding devices often feature full casings or cabinets and integral interfaces.
Resources:
DATAQ INSTRUMENTS - Waveform Analysis Using The Fourier Transform
United Electronic Industries - Data Acquisition Systems
National Instruments - Monitoring Applications with Data Acquisition Hardware
Read user Insights about Data Acquisition Systems and Instruments
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Bridge Conditioners
Bridge conditioners are instruments that provide excitation and support for strain gages, Wheatstone bridges, load cells, and sensors. They also include circuitry for signal conditioning, amplification, and processing.
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Charge Amplifiers and Charge Converters
Charge converters and charge amplifiers convert the charge output from a piezoelectric, capacitive or other charge-producing sensor to a signal such as analog voltage or current.
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Encoder and Resolver Signal Conditioners
Encoder and resolver signal conditioners accept encoder and resolver measurements and convert or condition these signals into digital data or suitable levels.
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Frequency-to-Voltage Converters
Frequency-to-voltage converters accept a signal and convert its frequency to a corresponding analog voltage level.
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Signal Filters
Signal filters block or decrease (attenuate) unwanted frequencies or signal wave characteristics.
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Temperature Signal Conditioners
Temperature signal conditioners accept outputs from temperature measurement devices such as resistance temperature detectors (RTDs), thermocouples, and thermistors. They then filter, amplify, and/or convert these outputs to digital signals, or to levels suitable for digitization.
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Voltage-to-Frequency Converters
Voltage-to-frequency converters accept a voltage signal and convert its analog level to a signal with a corresponding frequency.
