Editing Data acquisition (section)

==Methodology==

===Sources and systems===

Data acquisition begins with the [[physical phenomenon]] or [[physical property]] to be measured. Examples of this include temperature, vibration, light intensity, gas pressure, fluid flow, and force. Regardless of the type of physical property to be measured, the physical state that is to be measured must first be transformed into a unified form that can be sampled by a data acquisition system. The task of performing such transformations falls on devices called ''sensors''. A data acquisition system is a collection of software and hardware that allows one to measure or control the physical characteristics of something in the real world. A complete data acquisition system consists of DAQ hardware, sensors and actuators, signal conditioning hardware, and a computer running DAQ software. If timing is necessary (such as for event mode DAQ systems), a separate compensated distributed timing system is required.

A [[sensor]], which is a type of ''[[transducer]]'', is a device that converts a physical property into a corresponding electrical signal (e.g., [[strain gauge]], thermistor). An acquisition system to measure different properties depends on the sensors that are suited to detect those properties. Signal conditioning may be necessary if the signal from the transducer is not suitable for the DAQ hardware being used. The signal may need to be filtered, shaped, or amplified in most cases. Various other examples of signal conditioning might be bridge completion, providing current or voltage excitation to the sensor, isolation, and linearization.  For transmission purposes, [[Single-ended signalling|single ended]] [[analog signals]], which are more susceptible to noise can be converted to [[Differential signaling|differential signals]]. Once digitized, the signal can be encoded to reduce and correct transmission errors.

===DAQ hardware===

DAQ hardware is what usually interfaces between the signal and a PC. It could be in the form of modules that can be connected to the computer's ports ([[parallel port|parallel]], [[serial port|serial]], [[USB port|USB]], etc.) or cards connected to slots ([[S-100 bus]], AppleBus, ISA, [[Micro Channel architecture|MCA]], PCI, PCI-E, etc.) in a [[motherboard|PC motherboard]] or in a modular crate ([[Computer Automated Measurement and Control|CAMAC]], [[Nuclear Instrumentation Module|NIM]], [[VMEbus|VME]]). Sometimes adapters are needed, in which case an external [[breakout box]] can be used.

DAQ cards often contain multiple components (multiplexer, ADC, DAC, TTL-IO, high-speed timers, RAM). These are accessible via a [[Bus (computing)|bus]] by a [[microcontroller]], which can run small programs. A controller is more flexible than a hard-wired logic, yet cheaper than a CPU so it is permissible to block it with simple polling loops. For example:
Waiting for a trigger, starting the ADC, looking up the time, waiting for the ADC to finish, move value to RAM, switch multiplexer, get TTL input, let DAC proceed with voltage ramp.

Today, signals from some sensors and Data Acquisition Systems can be streamed via Bluetooth.

=== DAQ device drivers ===
DAQ [[device drivers]] are needed for the DAQ hardware to work with a PC. The device driver performs low-level register writes and reads on the hardware while exposing API for developing user applications in a variety of programs.

===Input devices===
*[[3D scanner]]
*[[Analog-to-digital converter]]
*[[Time-to-digital converter]]

===Hardware===
*[[Computer Automated Measurement and Control]] (CAMAC)
*[[Industrial Ethernet]]
*[[Industrial USB]]
*[[LAN eXtensions for Instrumentation]]
*[[Network interface controller]]
*[[PCI eXtensions for Instrumentation]]
*[[VMEbus]]
*[[VXI]]

===DAQ software===
Specialized DAQ software may be delivered with the DAQ hardware.  Software tools used for building large-scale data acquisition systems include [[EPICS]]. Other programming environments that are used to build DAQ applications include [[ladder logic]], [[Visual C++]], [[Visual Basic]], [[LabVIEW]], and [[MATLAB]].