-------------------------Monitor------------------------ The Newsletter for PC-Based Data Acquisition and Control Issue 81 www.windmill.co.uk April 2005 --------------------ISSN 1472-0221---------------------- Welcome to April's edition of Monitor. We hope you find it useful, but should you wish to cancel your subscription you can do so at http://www.windmill.co.uk/newsletter.html CONTENTS ======== * Windmill News: Free Software Used for Materials Testing * Windmill Notes: PID Control * Excel Corner: Virtual Instruments in Excel? ________________________________________________________ ________________________________________________________ Windmill News: Free Software Used for Materials Testing ________________________________________________________ Springfield Metallurgical Services are a company specialising in materials testing and analysis. As part of their work they use an Artech S-type tension- compression load cell, which is connected to a Transcell TI500E display. The Transcell display sends weight readings to the PC over an RS232 link. Originally the company used the Windows Hyperterminal program to collect the data. Hyperterminal worked fine but they needed the option of another channel of data. After considering two other programs they decided to use Windmill. Windmill can handle any number of channels of data, and is free to Monitor subscribers at http://www.windmill.co.uk/rs232.html A more recent version of the software is available from from https://www.windmillsoft.com/daqshop/rs232-modbus.html The free Windmill package features a universal driver for instruments that send or accept ASCII messages over RS232. It automatically feeds data from the instruments to Windows application software like Excel. The package also includes data logging, charting and output control software. These are ready-to-run applications: no programming is required. For help using Windmill with a Transcell Display see http://www.windmill.co.uk/transcell.html For more on Springfield Metallurgical Services see http://www.smslab.net/ ________________________________________________________ ________________________________________________________ Windmill Notes: PID Control ________________________________________________________ You can add PID (proportional, integral, derivative) control to a Windmill system with the optional Test-Seq program. Amongst other things this lets you monitor analogue inputs and stabilise conditions if readings don't comply with those desired. It does this by comparing the readings with your ideal input values, or set points. If there is a discrepancy it will output an appropriate control value. This is the sum of the Proportional, Integral and Derivative values. This is a function of the magnitude and duration of the error, and the rate of change of the measured value. Proportional control is the error multiplied by a Gain constant. This can be effective on its own for some applications, but for others you need to add integral or differential control, or both. Integral control is used to add long-term precision to a control loop. It is almost always used in conjunction with proportional control. It averages its input signal, which tends to kill noise. It can reduce overshoot and settling time. When derivative control is added, this may increase the stability of the system, reduce overshoot and improve the response time. Test-Seq isn't just for PID control, it has a wide range of commands which you can send to your devices or other Windmill programs. For more information about Test-Seq see https://www.windmillsoft.com/daqshop/test-control.html or contact [email protected] For more on PID control see... sci.engr.* FAQ on PID Controller Tuning PID Controllers: Theory, Design and Tuning Handbook of PI and PID Controller Tuning Rules ________________________________________________________ ________________________________________________________ Excel Corner: Virtual Instruments in Excel? ________________________________________________________ A virtual instrument is a computer-based representation of a real measurement instrument. For example, as a temperature changes a PC thermometer would rise and fall. Excel isn't the ideal software for this type of application, but you can create some interesting effects using its charting features. For instance, you can depict a liquid level as a part-filled tube. Here is a brief guide to get you started. It assumes you have a cell with a live data link to Windmill, which automatically updates a level reading. 1. Select the cell holding the level reading. 2. Insert a chart. 3. Choose column as the chart type, and clustered column as the sub-type (the default option) 4. Click Next twice to arrive at step 3 of the Chart wizard. 5. Remove the x axis label, choose not to show the legend, set oC as the Title of the Y axis and under Data Labels select Show Value. 6. Click Next and Finish the chart. 7. Double-click the column and from the Patterns tab select Fill Effects. A vertical graduated fill looks good, giving a cylindrical 3D appearance. 8. In Options set the Gap width to 0. If this makes your column too wide, resize the chart. (You may then have to alter the font of the axis. Double-click the Y axis and select the Font tab.) You can take this further. For examples of a range of thermometer styles see the AJP Excel Information site at http://www.andypope.info/charts/thermometer.htm Another way to show information is with a gauge or speedometer. You can achieve this with a combination of a donut chart and one or more scatter chart series. For how to do this see the Peltier Technical Services site at http://peltiertech.com/Excel/Charts/Speedometer.html Further Reading =============== For tips on using Excel with Windmill see http://www.windmill.co.uk/excel/ For charting tips see http://www.windmill.co.uk/excel/excel-charting.html For tips on designing a user interface see http://www.windmill.co.uk/interface.html ________________________________________________________ ________________________________________________________ * 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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