DAQ Series: How DAQs work at a high level

As Daniel Carnes (Facebook reader) said, “As more and more data acquisition systems make their way into our lives it is good to know how they work at least at a high level.”

Taking a cue from Mr. Carnes, engineers are no longer stereotyped as the person wearing the white coat in a lab. We are expecting more from computers and software programs, entailing multiple actions, to effect desired tested results.

Data Acquisition (DAQ) has become an industry standard term referring to almost any type of computer based system comprised of analog and/or digital inputs and outputs. Most systems are based upon PCs, but there is still a large market for systems based upon other platforms such as VME (Versa Module Europa: a flexible open-ended bus system making use of the Eurocard standard introduced by Motorola, Phillips, Thompson, and Mostek in 1981), and PXI, as well as those based on proprietary embedded controllers.

Because of the revolution of inexpensive personal computers, there is a demand for the use of PCI (Peripheral Component Interconnect: a local bus standard developed by Intel Corporation), PXI/CompactPCI (PCI extension), PCMCIA, USB, IEEE1394, ISA, or parallel or serial ports for data acquisition in laboratory research, test and measurement, and industrial automation. Many applications use plug-in boards to acquire data and transfer it directly to computer memory.

Others use DAQ hardware remote from the PC coupled through parallel or serial port. Its hardware is either internal and installed directly into an expansion slot inside your computer, or external and connected to your computer through an external cable. For example, VXI modules are installed in an external VXI chassis, and data is transferred between MATLAB and the module using an external link such as FireWire (IEEE 1394). Obtaining proper results from a PC-based DAQ system depends on each of the following system elements: Personal computer, transducers, signal conditioning, DAQ hardware, and software.

As previously stated in What is a Data Acquisition (DAQ), there are certain terms analogous with DAQs. However, there are elements or functions in a DAQ, which are: data collection, measurement, timing and triggering, a real-time clock, system control, data communication and data archiving. Every element must be in place for a structure to be considered a DAQ. If only a few of these elements are part of the system, then the module could be defined as a component of a DAQ system. If a system has all seven elements, along with additional features, it is probably a larger system as part of the larger structure.

Along with system elements, the actual components or elements of a DAQ used to perform the essential functions are critical to the efficiency of the system. There must be a series of sensors as inputs to a Data Acquisition Board; in addition, there must be a trigger to synchronize the sensor inputs (the data stream), as well as a control for the Data Acquisition Board. Between the Data Acquisition Board and the processor of the system and system clock, a data communications bus (I/O) is also required. While the data is being stored real-time, the analysis and review of the information is performed after data is gathered. The Data Acquisition System must collect, sort, catalog and store data to be reviewed and analyzed in a meticulous (read: offline) manner.

Special thanks to National Instruments, Engineer’s Edge, and MathWorks.