-------------------------Monitor------------------------ The Newsletter for PC-Based Data Acquisition and Control Issue 49 www.windmill.co.uk August 2002 --------------------ISSN 1472-0221---------------------- Welcome to the August edition of Monitor. This month it's our fourth birthday and we now have almost 20 000 subscribers - many thanks to you all. Today we're very pleased to bring news of how Windmill software played a key part in a coral-reef conservation study recently published in Hydrobiologia. We also highlight things to think about when choosing hardware to measure voltages. We only send this newsletter to people who have subscribed - should you wish to cancel your free subscription please do so at http://www.windmill.co.uk/newsletter.html CONTENTS ======== * Windmill News: Windmill Software is Cornerstone of Scientific Paper * Monitoring Voltage Signals - Considerations when Choosing DAQ Hardware * Exhibitions ________________________________________________________ ________________________________________________________ Windmill News: Windmill Software is Cornerstone of Scientific Paper ________________________________________________________ A paper recently published in the scientific journal Hydrobiologia, tells how the free Windmill software suite enabled marine biologists to devise a low-cost, high- performance procedure for automatic seafloor mapping. This has particular relevance for coral reef conservation in developing nations, as a snapshot of coral condition at the current time can be mapped. However, the method is also useful for aquaculture, salvage, SCUBA diving, fishing and other marine biology applications. Previously accurate seafloor mapping and classification was an expensive undertaking requiring sophisticated equipment. This excluded low-budget groups in developing nations. In this study the scientists used our free software, an old 486 PC, an inexpensive echo sounder and gps receiver. They used simple synchronisation techniques to integrate videoed environmental data. From a small boat they mapped a Malaysian coral-reef area of 114 hectares in 6 hours, matching rates that up until now had only been achieved with air-borne imaging devices. However, improving on existing methods Windmill software allowed "ground-truthed" data that can be classified according to many schemes by direct observation of the habitat. It also provides detailed depth data that satellite imaging or air-borne spectrographic sensors do not provide. The study concluded that the seafloor and coral reef mapping methodology described is so cheap that it is available to individual scientists in developing nations. As far as is known it is at the moment the only procedure that offers low-budget scientists a financially viable option for rapid mapping of both bathymetry and habitat characteristics of reef habitats on scales up to hundreds of square kilometres. As such, it is anticipated that this methodology may play a significant role in reef conservation efforts in developing nations. More Details ============ To read the entire paper see: A low-cost procedure for automatic seafloor mapping, with particular reference to coral reef conservation in developing nations Hydrobiologia 474(1): 67-79; Apr 2002 Trond-Inge Kvernevik; Mohd Zambri Mohd Akhir; Jill Studholme http://www.kluweronline.com/issn/0018-8158 For details of the free software used, and step-by-step instructions, see http://www.windmill.co.uk/seafloormapping.html ________________________________________________________ ________________________________________________________ Monitoring Voltage Signals: Considerations when Choosing DAQ Hardware ________________________________________________________ Many sensors (the pieces of kit that detect physical parameters like temperature, strain or pressure) produce voltage signals. In fact, voltage is the signal most commonly interfaced by a computerised data acquisition and control (DAQ) system. Before the computer can process and store the voltage reading, however, the DAQ interface will need to condition the signal - amplify or filter it for instance - and then convert it to a digital number which the computer can deal with. When choosing an interface for voltage measurements, three important things to consider are amplitude, frequency and duration. * Amplitude ========= A data acquisition system's analogue-to-digital converter is often calibrated for input voltages in the range 0-10 V. However, voltages from sensors such as thermocouples or strain gauge bridges may need to be amplified 1000 times to make it to a 0-10 V signal. For these types of measurements in-built amplification is generally offered as standard, making the DAQ interface capable of directly handling low voltage inputs from a few millivolts to a few volts. If your signal is smaller than a few millivolts, you may need to consider more specialised hardware. Alternatively you could amplify the signal before it reaches the DAQ hardware. If your signal is larger than the maximum accepted by the A-D converter you can divide the signal down using a resistor network. * Frequency ========= Before making a decision on data acquisition hardware, consider the highest frequency that you want to record. This helps you decide the speed of the hardware you need, and any filtering requirements. Noise may be present at higher frequencies than those you are trying to log, and you will need to be aware of it. You can remove noise by filtering the signal before digitising it. (See Monitor Issue 8 for more on filtering.) The highest frequency component of the signal determines how often you should read the input - in theory at least twice the highest component. However, you will need 10 to 20 points in a cycle to get a reasonable picture of a sinusoid. If you have more than one input, but only one A-D converter, the overall sampling rate will need to go up in proportion to the number of inputs. For slowly changing, essentially DC signals all that is necessary is to consider the minimum time for a significant change in the signal. * Duration ======== For how long do you want to sample the signal? If you are recording the data then the duration determines the storage required. This may be on computer disk or in the memory of the DAQ hardware. The format of the stored data will also affect the amount of storage space required. * Other Considerations ==================== There are obviously many other things to consider when choosing data acquisition hardware: compatibility with existing systems, software support, cost, expandability, method of connection to the computer, and so on. We hope this article has pin-pointed the specifics of the voltage measurement part of the picture. * Further Reading =============== The Microlink Measurement and Control Systems Catalogue has notes on sampling voltage inputs. This is available free from Biodata Ltd at http://www.microlink.co.uk/contact.html Related Monitor Articles Monitor Issue 3, Analogue Signals and Types of A-D Converter Monitor Issue 8, Filtering Monitor Issue 10, Specifying a Data Acquisition System ________________________________________________________ ________________________________________________________ Exhibitions and Conferences ________________________________________________________ Continuing our bi-monthly listing of exhibitions and conferences related to data acquisition and control. IEEE AutotestCon 2002 21-24-August Huntsville Al USA Conference focusing on automated test and related technology for military, government and aerospace applications. http://www.autotestcon.com/ Scanlab 2-5 September Bella Center Copenhagen Denmark Fair and conference for laboratory equipment, measuring technology and process control. http://www.scanlab.dk/ Instrumentation Scotland and Offshore Systems 4-5 September Aberdeen UK http://www.instrumentation.co.uk/ ATDC 2002 12-14 September Slavonski Brod, Croatia A forum to exchange scientific, technology and manufacturing knowledge between Western Europe and Central and Eastern Europe. Topics include product development, production technologies, information technology, quality assurance and measurement. http://www.sfsb.hr/atdc2002/atdc2002.html Sensors Expo 23-26 September World Trade Center Boston USA Brings together the technologies that are shaping sensing, data acquisition, control and communications. http://www.sensorsexpo.com/ Wescon North America 24-26 September Anaheim Convention Center California USA Exhibition including test & measurement and hardware & software design. http://www.wescon.com/ Nepcon 1-3 October NEC Birmingham UK Into its 36th year, Nepcon includes test, measurement and inspection equipment for the electronics industry. http://www.nepcon.co.uk/ ISA 2002 21-24 October Chicago USA Instrumentation, systems and automation conference and exhibition. Includes emerging technologies, keynote addresses and more than 30 specialised training courses. https://www.isa.org/customsource/isa/isa2002flash.html Energy Efficiency Expo 22-24 October Olympia 2 London UK Promoting energy management systems, metering and monitoring, building control and data management. http://www.energy-expo.org/ HET Instrument 2002 4-8 November Jaarbeurs Utrecht Netherlands The event for industrial automation and laboratory technology. http://www.hetinstrument.nl/ NAVSAT 2002 12-15 November Nice Acropolis France Dedicated to navigation and positioning applications. http://www.navsat-show.com/ ISA South America 19-22 November ITM EXPO Fairs & Convention Center São Paulo Brasil Features new technology, applications and products for instrumentation, systems and industrial automation. https://www.isa.org/ BIAS 2002 19-23 November Milan Trade Fair Italy Thirtieth international automation, instrumentation and microelectronics conference and exhibition http://www.ilb2b.it/ IT & Automation 2002 26-28 November Nurnberg Germany This exhibition takes the view that the continuous flow of information - from sensor to boardroom - is turning into the crucial factor for success in production-oriented companies. It therefore features all things realated to this. http://www.mesago.de/ ________________________________________________________ * Copyright Windmill Software Ltd * Reprinting permitted with this notice included * For more articles see http://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 is at http://www.windmill.co.uk/newsletter.html and an index of articles at http://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] http://www.windmill.co.uk/ https://www.windmillsoft.com/
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