-------------------------Monitor------------------------ The Newsletter for PC-Based Data Acquisition and Control Issue 122 www.windmill.co.uk September 2008 --------------------ISSN 1472-0221---------------------- Welcome to Monitor. I hope you enjoy the newsletter but if you do want to remove yourself from our mailing list please go to http://www.windmill.co.uk/newsletter.html CONTENTS ======== * Happy Birthday Monitor Newsletter * Debugging Noisy Measuring Systems * Custom Number Formats in Excel: A Postscript * DAQ News Roundup ________________________________________________________ ________________________________________________________ Happy Birthday Monitor Newsletter ________________________________________________________ It is now 10 years since we launched Monitor and we'd like to thank you all for subscribing and making the newsletter a success. Over the years your contributions and comments have pushed us in new directions and made sure that the newsletter has stayed relevant. We even appreciate your criticisms - so please keep writing to us and we'll try to keep going for another 10 years. ________________________________________________________ ________________________________________________________ Debugging Noisy Measuring Systems ________________________________________________________ Recently a customer contacted Windmill to see if we could help fix their pH monitoring system, which was showing fluctuating readings. They sent the system - a Microlink 751 USB with a pH connection box - to us to test. Our tests, though, showed nothing wrong and we deduced that the data acquisition equipment was not the source of the problem. pH monitoring systems are very sensitive and prone to interference. Small current or voltage surges can cause large fluctuations in readings. Here are some simple tests that you can follow to determine the cause of pH (or other) measurement problems. We've used the Microlink 751 hardware, from Biodata, as an example, but many of the tips also apply to other manufacturer's systems. Work through the tests one-by-one, eliminating sources of error as you go. 1. Check that the data acquisition (DAQ) unit is working properly. First remove other factors in the system that might be causing the problem, then check the DAQ unit itself. a. Remove any power signal conditioner. This provides surge protection and noise filtering. It should remove interference from other equipment but a faulty one could cause its own problems. b. Move the DAQ unit to another location. If you are using it in a laboratory for example, take it home. c. Connect your DAQ unit to a different laptop running on battery power, not on mains power. d. Now you can test whether the DAQ unit is the source of the noisy, fluctuating, data. Connect together the first positive input pin, the first negative input pin and the 0 V input pin. With the Microlink 751 these inputs are on pins 20, 1 and 19. You could use paperclips to connect the three pins. Leave all other inputs unconnected. As you have now shorted out the Microlink, if it is working correctly it will produce a reading of zero. If not the fault lies with the Microlink and you should contact Technical Support and send the unit back. If the reading is zero then the problem is very unlikely to be caused by the Microlink and you can go on to step 2. 2. Once you have eliminated the DAQ unit as the source of the fault, test the power supply to the computer. Plug the laptop into the mains - the reading should still be zero. 3. Reconnect any power signal conditioner. Again, check that the reading is zero. 4. Test the probes one-by-one. Place a pH probe in a known solution and see if the reading is as expected. Keeping the signal wires short and far away from electrical machinery helps reduce noise. You may also need to clean your electrodes. 5. Move everything back to the original location. If the readings become erratic go through the tests again. 6. Disconnect from the laptop and connect to the original computer. Again, if you now get noisy readings repeat the tests. 7. Finally make your measurements in a real situation. Discovering at which stage the problem occurs will let you identify the source and take remedial action. Further Reading: ================ Microlink 751 USB Unit https://www.windmillsoft.com/daqshop/daq-usb.html Monitor Issue 92, How to use a computer to measure pH http://www.windmill.co.uk/monitor92.html Monitor Issue 11, Differential v single-ended inputs http://www.windmill.co.uk/differential.html ________________________________________________________ Custom Number Formats in Excel: A Postscript ________________________________________________________ ________________________________________________________ Last month we published an article about ways to use Excel's custom number feature. (You can read this at http://www.windmill.co.uk/monitor121.html.) In it we discussed how using the # symbol specifies rounding to a significant digit. For example, the custom format .## would cause 12.3456 to be shown as 12.35. One of our subscribers, Professor Chris van Zyl, pointed out that the 0 symbol has a similar function to the # symbol, but forces a zero if necessary. For example, the custom format: #.##### would cause 0.3456 to be shown as .3456 0.##### would cause 0.3456 to be shown as 0.3456 0.####0 would cause 0.3456 to be shown as 0.34560 Thanks Chris for that addition. ________________________________________________________ ________________________________________________________ DAQ News Roundup ________________________________________________________ Welcome to our roundup of the data acquisition and control news. If you would like to receive more timely DAQ news updates then grab our RSS newsfeed at https://www.windmillsoft.com/monitor.xml. Read http://www.windmill.co.uk/newsfeed.php for notes on how to display the news on your own web site, read it via e-mail, mobile phone or in your browser. Secrets of Effective Communication beneath the Sea If researchers can better understand how physical conditions, like choppy seas and rocky bottoms, distort sound as it travels through the ocean, they could send data underwater faster and with less power and could make it much easier for networks of sensors to talk to each other simultaneously. They could improve wireless communications from ocean instruments and potentially eliminate the need for vehicles to surface just to transmit modest amounts of data. With these goals in mind, a team led by Scripps Institute of Oceanography has successfully completed a three-week study. Source: SCUBA Diving News http://news.scubatravel.co.uk/ Wireless Sensor Networks are a Good Investment According to new analysis from Frost and Sullivan, wireless sensor networks now provide a demonstrable return on investment. As sensors become an integral part of most industries, their high-volume applications have increased their efficiencies of scale, thus in turn lowering prices and promoting adoption in other devices. Source: Frost and Sullivan http://tinyurl.com/3qac8m Making Measurements Measure Up to Standards Information standards enable common activities. For instance, bring your laptop anywhere in the world and you will quickly and cheaply find a wireless Internet connection - due to the globally adopted WiFi standards. Researchers at the National Institute of Standards and Technology (NIST) are working to enable "WiFi-quality" information standards for manufacturing metrology systems. In this pursuit, they have developed DMIS which is a language for performing dimensional measurements. DMIS allows measurement program portability without requiring expensive translators. Source: NIST https://www.nist.gov/public_affairs/techbeat/ Strong Showing for Industrial Controls Demand for industrial control equipment in the USA improved during the second quarter, according to NEMA's Primary Industrial Controls Index. Manufacturing activity, though not at the level of two years ago, has remained resilient. Source: Nema http://www.nema.org/ Wireless sensors learn from life European and Indian researchers are applying principles learned from living organisms to design self-organising networks of wireless sensors suitable for a wide range of environmental monitoring purposes. Source: ICT Results http://cordis.europa.eu/ ________________________________________________________ ________________________________________________________ * 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/
To receive Monitor every month please fill in your e-mail address below. We will not pass your address to any third parties, nor send you any unsolicited e-mail.
You will receive an e-mail confirming your subscription, with details of how to download the free software. If you don't receive this then your spam filter may be blocking our message. Make sure it is set to accept messages from [email protected] If you have problems contact the Editor.