| Data acquisition starts with the physical property | | | | · General Purpose Interface Bus |
| of an object to be measured that is analyzed and | | | | (GPIB) |
| stored in the computer for long term purposes. | | | | Synonymous with HPIB (for Hewlett-Packard), the |
| In short data acquisition systems are also | | | | standard bus used for controlling electronic |
| referred to as DAS or DAQ which generally | | | | instruments with a computer. Also called IEEE 488 |
| includes acquisition of signals and waveforms and | | | | in reference to defining ANSI/IEEE standards. |
| then interpretation of signals to obtain desired | | | | |
| information. These different properties which are | | | | · Resolution |
| analyzed through data acquisition are facts such | | | | The smallest signal increment that can be |
| as temperature, pressure, density, viscosity etc. | | | | detected by a data acquisition system. Resolution |
| | | | | can be expressed in bits, in proportions, or in |
| Data acquisition systems have a huge use in | | | | percent of full scale. For example, a system has |
| scientific and medical research purposes such as | | | | 12-bit resolution, one part in 4,096 resolutions, and |
| magnetic resonance imaging, microelectrode | | | | 0.0244 percent of full scale. |
| recording, and Eco cardiology, remote monitoring, | | | | |
| laser Doppler flow etc. | | | | · RS232 |
| | | | | It’s a standard for serial communications |
| They serve as an important part of gathering any | | | | found in many data acquisition systems. RS232 is |
| vital information using data analysis software and | | | | the most common serial communication, |
| equipments. | | | | however, it is somewhat limited in that it only |
| | | | | supports communication to one device connected |
| Some of the common forms of data acquisition | | | | to the bus at a time and it only supports |
| at larger scale are seismic data acquisition, | | | | transmission distances up to 50 feet. |
| wireless data acquisition, pc data acquisition and | | | | |
| SCADA (supervisory Control and Data Acquisition) | | | | · RS485 |
| which is the most widely used system referring | | | | It’s a standard for serial communications |
| to a computer system monitoring industrial, | | | | found in many data acquisition systems. RS485 is |
| infrastructure or facility based processes like | | | | not as popular as RS232, however, it is more |
| manufacturing, production, power generation, | | | | flexible in that it supports communication to more |
| water treatment distribution and energy | | | | than one device on the bus at a time and |
| consumption. | | | | supports transmission distances of approximately |
| | | | | 5,000 feet. |
| Let’s get familiar with some more technical | | | | |
| terms in data acquisition: | | | | |
| | | | | - Sample Rate |
| · Analog-to-digital converter (ADC) | | | | The speed at which a data acquisition system |
| An electronic device that converts analog signals | | | | collects data. The speed is normally expressed in |
| to an equivalent digital form. The analog-to-digital | | | | samples per second. For multi-channel data |
| converter is the heart of most data acquisition | | | | acquisition devices the sample rate is typically |
| systems. | | | | given as the speed of the analog-to-digital |
| | | | | converter (A/D). To obtain individual channel |
| · Digital-to-Analog Converter (D/A) | | | | sample rate, you need to divide the speed of the |
| An electronic component found in many data | | | | A/D by the number of channels being sampled. |
| acquisition devices that produce an analog output | | | | |
| signal. | | | | - Single-ended Input (SE): |
| | | | | Refers to the way a signal is wired to a data |
| · Digital Input/Output (DIO) | | | | acquisition device. In single-ended wiring, each |
| Refers to a type of data acquisition signal. Digital I | | | | analog input has a unique high connection but all |
| O is discrete signals which are either one of two | | | | channels share a common ground connection. |
| states. These states may be on/off, high/low, 1 | | | | Data acquisition devices have either single-ended |
| 0, etc. Digital I/O is also referred to as binary I/O. | | | | or differential inputs. Many support both |
| | | | | configurations. |
| · Differential Input | | | | |
| Refers to the way a signal is wired to a data | | | | With the progress in technology data acquisition |
| acquisition device. Differential inputs have a unique | | | | has become more advanced and reliable have |
| high and unique low connection for each channel. | | | | come all the way from using simple devices to |
| Data acquisition devices have either single-ended | | | | highly sophisticated computer systems and has |
| or differential inputs, many devices support both | | | | proved to be the greatest engineering marvel in |
| configurations. | | | | achieving data precision. |
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