28 July 2000
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-----------------------------Monitor----------------------------- The Newsletter for PC-Based Data Acquisition and Control Issue 24 www.windmill.co.uk July 2000 -------------------------ISSN 1472-0221-------------------------- Welcome to issue 24 of Monitor from Windmill Software. Today we are pleased to announce that Windmill is now available for USB data acquisition units! These plug into the computer's universal serial bus port. We discuss USB below, highlighting its benefits for measurement and control. We only send this newsletter to people who have subscribed - should you wish to cancel your free subscription please visit https://www.windmill.co.uk/newsletter.html CONTENTS ======== * Windmill News: New USB Unit Uses Windmill * What is the universal serial bus? * Data acquisition abbreviations explained _________________________________________________________________ Windmill News: New USB Unit Uses Windmill The new USB unit from Biodata takes full advantage of the Windmill software suite. Called the Microlink 751, the unit lets you: * measure voltage, current, temperature and strain * switch digital outputs * monitor digital inputs * count up to 65535 You simply plug the compact Microlink 751 into the computer's USB port - no need to switch off your PC or even restart Windows. With the powerful yet easy-to-use Windmill applications you can be logging, charting and counting in no time. To discover just how easy it is, visit https://www.windmillsoft.com/ The Microlink 751 and Windmill software package costs just 595 British pounds (around 895 US dollars or 945 euros). This includes free technical support for life and a money back guarantee if not absolutely satisfied. For secure ordering go to https://www.windmillsoft.com/ _________________________________________________________________ What is the Universal Serial Bus? The USB is a relatively recent way to connect instruments and devices to the PC. Most new computers have one or two USB ports, in addition to the familiar RS232 (COM) and parallel ports. You can use the USB ports to connect peripherals like digital cameras, printers and data acquisition and control units. Why use the USB for Data Acquisition? ===================================== The USB is extremely convenient for data acquisition for several reasons. * The equipment can obtain power from the USB; it doesn't need to be battery powered or plugged into the wall. This makes USB ideal for portable data acquisition with a laptop. * Using a USB hub you can connect many devices to one USB port - letting you easily expand your system should requirements grow. * USB ports are provided on most new PCs - no need to open the computer and install adaptor cards. * You can plug in and unplug your equipment without switching off your computer or even restarting Windows. * The USB cable can be up to 5 m long. However, using USB hubs between cables you can reach 30m. * Faster speeds than those allowed by RS232 connections are achievable * You can use USB devices alongside existing data acquisition equipment (such as cards that you've installed in your PC or instruments that plug directly into the RS232 port). What about older PCs? ===================== If your PC does not have a USB port you can buy a PCI-based card which provides one. However, you need to be running Windows 98 or Windows 2000. (Early releases of Windows 95 do not support USB, later releases have some support but it's better to use Windows 98 or 2000.) You can test whether your PC is USB compatible by visiting www.usb.org and downloading their evaluation utility program. If you don't wish to upgrade your machine there are many other ways to connect data acquisition equipment to computers, such as Ethernet, RS232, RS485, Modbus or GPIB. Issue 2 of Monitor - https://www.windmill.co.uk/freewm.html - discusses a range of methods. Cable Details ============= The USB cable should have an "A" plug at one end (for the computer) and a "B" plug at the other: no sockets. Any other arrangement doesn't conform to the standard. The cable comprises four wires: two carry your signal data and two supply voltage. The bus can operate at two different speeds, depending on the attached device. The device itself tells the bus what its speed is through the voltage cables. The cable should not be longer than 5 metres for fast devices, or 3 metres for slow devices. However, you can use up to 5 USB hubs to connect cables, giving a maximum distance of 30 m. The Future for USB ================== In April this year the USB 2.0 specification was released. This allows for faster data transfer of 480 megabits per second. However, the specification has been designed to be totally compatible with the existing USB standard. The new specification was developed by the USB Promoter Group, which includes Compaq, Intel, Microsoft and Philips Semiconductors. Future upgrades are promised to have equal compatibility, so you can be sure that as technology advances so will your data acquisition system. Further Reading =============== USB Implementers Forum http://www.usb.org/ USB Complete, Axelson J, 1999. ISBN: 0965081931, Lakeview Research More details at amazon.co.uk or amazon.com. USB Explained, McDowell and Seyer, 1998. ISBN: 013081153X, Prentice Hall More details at amazon.co.uk or amazon.com. _________________________________________________________________ Data Acquisition and Control Abbreviations Continuing our acronym and other abbreviation reference guide. For A-M see Issue 22 and 23 of Monitor https://www.windmill.co.uk/monitor22.html https://www.windmill.co.uk/monitor23.html ODBC Open database connectivity Developed by Microsoft, a standard for accessing a database. By using ODBC statements in a program you can access files in a number of different databases, including Access, dBase and Text. In addition to the ODBC software, a separate module or driver is needed to access each database. http://www.microsoft.com/data/odbc/ OEM Original Equipment Manufacturer A company that makes basic hardware for other manufacturers to build into their products. OOP Object-Orientated Programming Languages using OOP include Visual Basic, Java and C++. http://catalog.com/softinfo/objects.html OS Operating System Examples include Windows, DOS and UNIX. PC Personal Computer Generally applied to computers conforming to the IBM designed architecture. PCB Printed Circuit Board PCI Peripheral Component Interconnect A local bus standard developed by in 1992. PCI cards plug into your computer and are configured through software. They do not have jumpers or switches. http://www.pc.ibm.com/us/infobrf/ibpci.html PCMCIA Personal Computer Memory Card International Association Industry group that developed the specification for credit card- sized plug-in cards for laptop computers. http://www.pc-card.com/ PD Proportional Derivative See PID pH potential of Hydrogen A measure of acidity. At 25 C (77 F) a neutral solution such as pure water has a pH of 7; a pH of less than 7 indicates acidity, more than 7 alkalinity. PI Proportional Integral See PID PI&D Piping and Instrumentation Diagram PID Proportional Integral Derivative Proportional gain, integral action time and derivative action time. A feedback method for control. PID software, for example, compares an analogue input value with a set point and if there is a discrepancy outputs an appropriate analogue or digital control value, according the PID calculations. PID Process and Instrumentation Design PLC Programmable Logic Controller A microprocessor-based device used in industrial monitoring and control. ppb Parts Per Billion ppm Parts Per Million ppt Parts Per Thousand PROFIBUS Process Fieldbus http://www.profibus.com/ PRT Platinum Resistance Thermometer A type of RTD (resistance temperature device) made of platinum. Has long term stability. Pt100 A PRT specified to have a resistance of 100 ohm at 0 oC. QA Quality Assurance QC Quality Control R&D Research and Development RF Radio Frequency Any frequency within the electromagnetic spectrum suitable for radio broadcasting and communications. Frequencies extend from 9 kilohertz to thousands of gigahertz. The RF spectrum is divided into several bands, including VHF and UHF. RFI Radio Frequency Interference rms Root mean square The square root of the sum of the squares of a set of quantities divided by the total number of quantities. Used when monitoring ac (alternating current) signals. Many power supplies, for example, issue an ac signal. This needs to be converted to a dc (direct current) signal for the PC interface. The solution is a signal conditioning input that produces a dc signal proportional to the rms of the amplitude of the input signal. The rms operation means the reading will always be positive. RTD Resistance Temperature Device or Resistance Thermometer Detector Rely on the principle that the resistance of a metal increases with temperature. https://www.windmill.co.uk/thermocouple.html RS232 Recommended Standard 232 A protocol for serial data communications. An RS232 link will run at up 38400 baud (bits per second) over short distances, and at lower speeds as the distance increases. You can plug the RS232 lead directly into the computer's serial (COM) port. RS485 Recommended Standard 485 Another protocol for serial communications. Allows several devices to be connected to a single cable, distributed over a wide area. SCADA Supervisory Control and Data Acquisition SCSI Small Computer Standard Interface SCSI is a parallel interface standard used by Apple Macintosh computers, PCs and many UNIX systems for attaching peripheral devices to computers. http://www.hardwarecentral.com/hardwarecentral/print/36/ S/H Sample and Hold A component of a type of analogue-to-digital converter. The analogue signal is frozen in a sample and hold circuit to prevent it changing during digitisation. https://www.windmill.co.uk/a-d.html SE Single-Ended An analogue input that is measured with respect to a common earth. Single ended inputs are only suitable for signals that are of good size - 100 mV full scale or above. SHTTP Secure-Hypertext Transfer Protocol An extension to the HTTP protocol to support sending data securely over the World Wide Web. SMTP Simple Mail Transfer Protocol. The Internet standard protocol for transferring electronic mail messages from one computer to another. Regulates the communication between mail servers. SI International system of units. Abbreviation for Systeme International (d'Unites). SP Set Point Value of a controlled variable, departure from which causes a controller to operate to reduce the error and restore the intended steady state. SPC Statistical Process Control A method to separate random variations in data from non-random variations. Used in automatic product testing. SQL Structured Query Language A query language for requesting information from a database. The original SQL was introduced in 1979 by Oracle Corporation. Supports distributed databases, spread over several computer systems. TCP/IP Transmission Control Protocol/Internet Protocol The communications language used between computers on the Internet. IP is the specification that determines where packets of information are routed to, based on their destination address. TCP makes sure that the packets arrive correctly at their destination address. If TCP determines that a packet was not received, it will try to resend the packet until it is received properly. TTL Transistor-Transistor Logic Referring to logic circuits consisting of two or more directly interconnected transistors, to provide conditional switching capability. For digital input circuits, a logic 1 is obtained for inputs of 2.0 to 5.5 V which can source 40 microA, and a logic 0 for inputs of 0 to 0.8 V which can sink 1.6 mA. For digital output signals, a logic 1 is represented by 2.4 to 5.5 V with a current source capability of at least 400 microA; and a logic 0 by 0 to 0.6 V with a current sink capability of at least 16 mA. UHF Ultra High Frequency Radio waves between 300 MHz and 3000 MHz. UPS Uninterruptable Power Supply Used to keep critical equipment, including computers, running in the event of a mains power failure. USB Universal Serial Bus A serial communications protocol for connecting peripherals to computers - is gradually replacing RS232 and parallel ports. VHF Very High Frequency Radio waves between 30 MHz and 300 MHz. WAN Wide area network. A network of circuits spanning a large region that is used to transmit data. XFMR Transformer Next month: It's Monitor's second birthday and we're including a complete index of all subjects covered in our previous issues. _________________________________________________________________ * Copyright Windmill Software Ltd * Reprinting permitted with this notice included * For more articles see https://www.windmill.co.uk We are happy for you to copy and distribute this newsletter, and use extracts from it on your own web site or publication, providing the above notice is included and a link back to our website is in place. An archive of previous issues - including articles on temperature and strain measurement - is at https://www.windmill.co.uk/newsletter.html Windmill Software Ltd, PO Box 58, North District Office, Manchester, M8 8QR, UK Telephone: +44 (0)161 833 2782 Facsimile: +44 (0)161 833 2190 E-mail: [email protected] https://www.windmill.co.uk/ https://www.windmillsoft.com/
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