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   Data Acquisition Systems Introduction

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The RS-232 Standard

Data acquisition devices are products and/or processes used to collect information to document and analyze some phenomenon. In the simplest form, a technician data logging the temperature of an oven on a piece of paper is performing data acquisition. As technology has progressed, this type of process has been simplified and made more accurate, versatile, and reliable through electronic equipment. Equipment ranges from simple recorders to sophisticated computer systems. Data acquisition products serve as a focal point in a system, tying together a wide variety of products, such as sensors that indicate temperature, flow, level, or pressure, acquiring signals to be proceessed to obtain the desired information. Some common data acquistion terms are shown below:

  • Analog-to-digital converter (ADC)
    An electronic device that converts analog signals to an equivalent digital form. The analog-to-digital (A-to-D) converter is the heart of most data acquisition systems.

  • Digital-to-Analog Converter (D/A)
    An electronic component found in many data acquistion devices that produce an analog output signal.

  • Digital Input/Output (DIO)
    Refers to a type of data acquistion signal. Digital I/O are discrete signals which are either one of two states. These states may be on/off, high/low, 1/0, etc. Digital I/O are also referred to as binary I/O.

  • Differential Input
    Refers to the way a signal is wired to a data acquisition device. Differential inputs have a unique high and unique low connection for each channel. Data acquisition devices have either single-ended or differential inputs, many devices support both configurations.

  • General Purpose Interface Bus (GPIB)
    Synonymous with HPIB (for Hewlett-Packard), the standard bus used for controlling electronic instruments with a computer. Also called IEEE 488 in reference to defining ANSI/IEEE standards.

  • Resolution
    The smallest signal increment that can be detected by a data acquisition system. Resolution can be expressed in bits, in proportions, or in percent of full scale. For example, a system has 12-bit resolution, one part in 4,096 resolution, and 0.0244 percent of full scale.

  • RS232
    A standard for serial communications found in many data acquistion systems. RS232 is the most common serial communication, however, it is somewhat limited in that it only supports communication to one device connected to the bus at a time and it only supports transmission distances up to 50 feet.

  • RS485
    A standard for serial communications found in many data acquistion systems. RS485 is not as popular as RS232, however, it is more flexible in that it supports communication to more than one device on the bus at a time and supports transmission distances of approximately 5,000 feet.

  • Sample Rate
    The speed at which a data acquisition system collects data. The speed is normally expressed in samples per second. For multi-channel data acquisition devices the sample rate is typically given as the speed of the analog-to-digital converter(A/D). To obtain individual channel sample rate, you need to divide the speed of the A/D by the number of channels being sampled.

  • Single-ended Input (SE):
    Refers to the way a signal is wired to a data acquisition device. In single-ended wiring, each analog input has a unique high connection but all channels share a common ground connection. Data acquisition devices have either single-ended or differential inputs. Many support both configurations.

12-Bit Multifunction Aanalog & Digital I/O Board: OME-A-8111
For PC/AT compatible computers, the OME-A-8111 offers 8 analog input channels, provides gains of 1, 2, 4, 8, 16 and has a maximum sampling rate of 30 KS/s.
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   Data Acquistion System Types
Serial Communication Data Acquistion Systems
Serial communcation data acquistion systems are a good choice when the measurement needs to be made at a location which is distant from the computer. There are several different communication standards, RS232 is the most common but only supports tranmission distances up to 50 feet. RS485 is superior to RS485 and supports transmission distances to 5,000 feet.
iDRX Series Serial Port Data Acquisition System
USB Data Acquistion Systems
The Universal Serial Bus (USB) is a new standard for connecting PCs to peripheral devices such as printers, monitors, modems and data acquistion devices. USB offers several advantages over conventional serial and parallel connections, including higher bandwidth (up to 12 Mbits/s) and the ability to provide power to the peripheral device. USB is ideal for data acquisition applications. Since USB connections supply power, only one cable is required to link the data acquisition device to the PC, which most likely has at least one USB port.
OMB-DAQ55 USB Data Acquisition Systems
Data Acquisition Plug-in Boards
Computer data acquisition boards plug directly into the computer bus. Advantages of using boards are speed (because they are connected directly to the bus) and cost (because the overhead of packaging and power is provided by the computer). Boards offered are primarily for IBM PC and compatible computers. Features provided by the cards can vary due to number and type of inputs (voltage, thermocouple, on/off), outputs, speed and other functions provided. Each board installed in the computer is addressed at a unique Input/Output map location. The I/O map in the computer provides the address locations the processor uses to gain access to the specific device as required by its program.
OME-PCI-1002 data Acquisition Plug-in Board
Parallel Port Data Acquistion Systems
The standard parallel port on a computer which is commonly used for a printer connection can also be used to connect to a data acquistion device. Parallel port systems often support very high sample rates, although the distance between the computer and the data acquistion device is limited to a few feet.
OMB-DAQBOOK Parallel Port Data Acquisition Systems
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