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28 June 2013

Windmill Software Ltd
Data Acquisition Intelligence
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The Newsletter for PC-Based Data Acquisition and Control
Issue 179           June 2013
--------------------ISSN 1472-0221----------------------

Welcome to the June issue of Monitor: I hope you find 
it useful. We've a new strain measurement package 
detailed below, example macros in Excel to save files 
every day and a new section answering some questions 
you've asked recently on using Windmill.  

For more measurement and control discussion and tips 
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Monitor Newsletter

* Monitor Strain Gauges over the Internet
* Excel Corner: Saving to a new File Every Day
* We Answer your Windmill Questions
* DAQ News Round-up

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Monitor Strain Gauges over the Internet ________________________________________________________ A new strain data logging package is now available from our on-line shop at It lets you log data over Internet or Ethernet networks. Strain data logger
  • Monitor strain gauges, pressure transducers or voltage signals, through 16 differential input channels
  • Can also monitor digital inputs, count, control digital outputs and measure temperature, pressure, flow, level, etc (extra hardware may be needed)
  • Includes Windmill Software: no programming required
  • Automatic ranging lets the software match the strain signal as closely as possible
  • Integrating analogue-to-digital converter reduces electrical noise
  • Use software to select the resolution of the A-D converter from 12- to 18-bits: choose between high resolution and high speed
  • Automatic recalibration
  • Set two alarms on each strain gauge
  • Measurements returned in microstrain, or engineering units of your choice
  • Use for real-time data acquisition on your PC or for stand-alone data logging
  • Free technical support for life and money-back guarantee if not satisfied
Measuring Strain The 851-SG package comprises an 851 data logger, a strain connection box and Windmill data acquisition software. Just connect your strain gauges to the strain box, plug the box into the 851 Data Logger and away you go. This method of connection means you can use the 851 Data Logger to monitor, for example, temperature at the same time as strain. With the 851-SG package you can monitor strain gauge bridges and balanced bridges such as pressure transducers. You can configure individual channels to accept any of these inputs:
  • voltage
  • quarter bridge: single strain gauge
  • half bridge: tensile + compressive strain gauge
  • half bridge: normal + transverse strain gauge
  • full bridge: 2 tensile + 2 compressive gauges
  • full bridge: 2 normal + 2 transverse gauges
  • full bridge: tensile normal + compressive normal + tensile transverse + compressive transverse gauge
Strain gauges need an external excitation voltage to supply sufficient current to keep all the bridge circuits energised. The 851-SG package provides four sets of 16 screw terminals giving + and - excitation and signals for each of 16 bridges. Two 1 kOhm termination resistors are mounted in half bridge configuration whilst high quality 350 and 120 Ohm resistors can be provided for the completion of quarter bridges. When a bridge input is selected the Windmill software monitors excitation voltage and performs the bridge calculation to produce a reading in microstrain. This eliminates errors due to changes in excitation voltage. The initial unstrained bridge measurement is often much larger than the change in signal due to strain. If this initial value is not accounted for, it restricts the resolution you can obtain - i.e. the smallest signal you can measure. Windmill software can zero or balance the bridge, nulling the offset of the initial voltage. So instead of measuring over a wide range, 0 to 0.5 V for example, you can choose a narrow range such as 0 to 0.01 V. Each range is divided into a fixed number of steps: the resolution. The smaller the range and the larger the resolution, the more precise the reading. The 751-SG offers a choice of resolutions from 12-bit for fast sampling to 18-bit for greater precision. More information:
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Excel Corner: Saving Logged Data to a New File Every Day ________________________________________________________ After last month's article on automatically saving an Excel file, a reader got in touch to ask how he could save data in a new file every day. He was using Excel to continually log data every 5 seconds. To save in a new file daily you need to add just a few lines of code to your logging macro. We give details below, and an example at 1. Add: Application.OnTime TimeValue("00:00:00"), "SaveNow" Where: TimeValue specifies the time of day to save the file. In our example at midnight. SaveNow is the name of a subroutine containing the instructions to save the file. 2. Create a new subroutine to save a copy of the current worksheet in a new file. We do it this way, rather than saving a copy of the current workbook (which would take less code), as we don't want to also save the data logging macros with each file. The subroutine should: a. Check whether the new filename exists (so as not to overwrite any existing file) b. Copy the worksheet and save it as a new file. c. Close the new file. For example Private Sub SaveNow() Dim Fname As String Fname = "Data" & Format(Now(), "yyyymmdd") & ".xls" If Dir(Fname) = "" Then ScreenUpdating = False Dim wb As Workbook Worksheets("Sheet1").Copy Set wb = ActiveWorkbook wb.SaveAs Fname wb.Close ScreenUpdating = True End Sub Notes: ScreenUpdating = False stops Excel redrawing the screen which may speed up the Save operation The file will be saved in the format Data20130620.xls, where 20130620 represents today's date ScreenUpdating = True re-enables the screen updates. Saving data log files every day in Excel The code saves a series of files every day. However, it doesn't delete the data once saved. So each file will contain all the previous days' data as well as its own. To save just that day's data, you will need to delete the contents of the main file after each save. Add this code to your SaveNow subroutine after changing data-logging.xls to your worksheet name, and Range("a2") to reference the cell holding the first data value: Workbooks("data-logging.xls").Sheets("Sheet1").Range("a2").Select Range(Selection, ActiveCell.SpecialCells(xlLastCell)).Select Selection.ClearContents It will select and delete everything below the first row, so each file will contain just that day's data. If you are nervous about automatically deleting data, you can use Windmill Logger to save data at the same time as Excel. That way you can be confident that you have a back-up that can later be imported into Excel if necessary. More Excel data logging macros are on our website at Have an Excel question or tip? Want more details on logging with Excel? Contact [email protected]
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Questions on Using Windmill ________________________________________________________ Welcome to our new, occasional, slot answering questions we've been asked this month about using Windmill. If you have a question e-mail [email protected] Question: We have an request for data logging via Modbus TCP/IP and we are evaluating your software Windmill 7 Data Acquisition Software. The customer wants us to generate a text file on a PC. This should work with your product, right? The additional requirement is that the software has to generate a new file every day. Is the software able to do that as well? Answer: The short answers are yes and yes. Windmill Logger saves data in text format, and can save to a new file every day. Subscribers can download a trial of Logger, and the rest of Windmill. The trial contains a software signal generator, which you can use to experiment with the Windmill programs without worrying about any hardware settings. Question: I have been working with ComDebug and gotten for the most part the results that I have wanted. I was able to parse the data correctly received from the scale, but I am not sure how to get an actual 'Real-Time' display from the scale. I don't know if its on the scale end or settings on the computer/software end to get the scale to read exatly what it says when told to. Right now it waits for the reading to balance out, and I miss quite a bit of readings. I will keep doing some research, but any additional help would be greatly appreciated! Answer: On most scales you can choose either to wait until a reading is stable, or to take a reading right away. How you do this depends on the scale. For example, with a Mettler scale you would use an S command to request a stable reading and SI to tell the scale to send the reading immediately. Other scales, like those from Sartorius, let you choose from four options covering Very Stable to Very Unstable. So change the settings on the scale to prevent missed readings. More details for how to do this on different balances are at
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DAQ News Round-up ________________________________________________________ Welcome to our round-up of the data acquisition and control news. If you would like to receive more timely DAQ news updates then grab our RSS newsfeed at Read for notes on how to display the news on your own web site or automatically tweet it. Better design tests needed for medical devices The medical technology sector needs better ways of demonstrating the safety, effectiveness and performance of its products, says a new report. Source: MIT Technology Review Snow sensing helps predict water shortages Precisely measuring supplies of meltwater could help farmers in the US plan what they plant in order to battle a changing climate. Source: New Scientist Materials Scientists Build Chlorophyll-Based Phototransistor Coat a layer of graphene with chlorophyll and you get a remarkably sensitive light-activated switch, say researchers at the Institute of Atomic and Molecular Sciences in Taiwan. Source: MIT Technology Review Intrinsic Safety Drives Process I/O Module Market According to a study by ARC Advisory Group, the global process automation I/O module market grew in 2012, but not by as much as in the previous two years. They predict that the process I/O module market will resume growth at an above average rate during the next five years. Source: ARC Advisory Group NIST Researchers Offer Tool to Aid Standards Implementation The nice thing about standards, it's been said, is that there are so many to choose from. Now comes a serious effort by National Institute of Standards and Technology (NIST) researchers to develop a computer-aided method for analyzing, comparing and testing standards, from the conceptual stage all the way through to implementation and beyond to rounds of updating and revising. Source: NIST ________________________________________________________ ________________________________________________________ * Copyright Windmill Software Ltd * Reprinting permitted with this notice included * For more articles see 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 and an index of articles at 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]


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