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March 2000

Windmill Software Ltd
Data Acquisition Intelligence
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Issue 20: Data Logging Tips


Windmill News | Data Logging Tips | Web Resources Update


Thank you for your technical support queries - they've enabled us to expand our FAQ page. Questions answered now include:

  • How to automatically start Windmill DDE Panel when you switch on the computer
  • How to store each data reading in a new cell in Excel
  • How to obtain weight readings rather than voltage readings

To see the answers to these and other questions go to


Last month we discussed getting to know the Windmill Software, with tips mainly for new users. This month we cover some advanced features of your free Logger software.


Logging Data Continuously to a Series of Files
Windmill comprises a suite of data acquisition programs. One of these, Logger, saves data to disk. For some applications, quality assurance for example, you will want to log data continuously. If you did this to just one file, it would obviously very quickly become too large and unmanageable. The answer is to instruct Logger to periodically close the current file and create a new one. You can choose any time scale to do this: choosing a number of minutes, hours, days or weeks. Logger identifies each file by an incrementing, 3-digit, number.

How to do this?

  1. In Logger, select DataFile from the menu bar
  2. Type a name for the files that are to hold the data. This must include three question marks. When Logger creates the file, it replaces the question marks by a number. For example, the file name might be data???.wl (wl stands for a Windmill Logger file). The first set of readings is stored in data001.wl, the second in data002.wl, etc.
  3. Check the "Periodically open new log file" box.
  4. Press the Settings button.
  5. Choose the length of time you want a file to be open and saving data.


Automatically Overwriting Old Data: Saving Disk Space
Although the above solution produces manageable file sizes, it doesn't stop the hard disk becoming full of data. What happens if you are only interested in data from the last week or month? Well, you can tell Logger to only store the last so many files. To give the last week's data, you might open a new file every day and save only the last 7. In this case you might have files labelled data001.wl to data007.wl. On the eighth day the contents of data001.wl will be overwritten, thus using disk space efficiently.

How to do this?

  1. Follow steps 1-4 above.
  2. Choose how many data files to store (between 1 and 999).


What Happens if I Stop Logging?
You might want to stop logging for a while but then restart to the same sequence of files. This is no problem. Press the Pause button and Logger will wait until you press Resume and then continue logging to the currently open file. (Unless you have paused for longer than your file interval, when Logger will save the data in the next file in the sequence.)

Press the Stop button instead of Pause, and Logger will close the file rather than just suspending logging. On subsequently pressing Start, Logger will ask if you want to append the data to the most recently open file, or to start from file 001 and overwrite its data. (If you have stopped for longer than your file interval, Logger will automatically start from file 001.)

To be safe then, if you want to keep all data, choose Pause. (However, if you want to open the file in other programs, before resuming logging, you must press Stop. Pause leaves the file open and it is therefore unavailable to any other software.)


How do I Later View and Analyse the Data?
Logger will display each reading as it collects it, with values outside alarm thresholds shown in blue (warning alarm) or red (critical alarm). Older data will eventually scroll off the top of the window. During data collection you can also use the Windmill Chart program, to show data graphically.

After collection has finished you have a choice of ways to see the data. You can, for instance, use Windmill's Replay program. This shows data as a moving chart which you can stop, rewind, fast forward, zoom into, zoom out of, etc. It also shows a table of the data values. You can buy Replay from our on-line catalogue for 195 pounds (around 310 dollars or 325 euros). For details visit our on-line catalogue.

Alternatively you can open the data in any third-party program accepting ASCII values (Excel, Access or Word for instance). You can choose how the columns of data are separated - by tabs, commas or spaces (good for sending directly to the printer or plotter).


We hope you have found these, and last month's, Windmill tips useful. If you have any queries about what Windmill can do for you, please get in touch.

For more information on Windmill programs please visit:
For the latest Help files see
For answers to questions others have asked about the free software see

Updates to our Previous Newsletters

In our newsletters of the last year we have highlighted useful (we hope) web sites on a variety of subjects. These include:

  • Magazines (Issue 16)
  • Standards (Issue 14)
  • Employment (Issue 11)
  • Book shops (Issue 10)

As more sites are coming on-line all the time, here's a brief update to those issues.


In Issue 16 of Monitor we revealed the best web magazines in the data acquisition and control field. In February another web site was launched, developed by the publisher of a range of engineering titles. Over 500 000 pounds has been invested in the site. It includes an archive of all the articles published in the past three years in magazines such as The Engineer, Control and Instrumentation, and Process Engineering.
Issue 14 ( discussed standards. Year 2000 revisions to the ISO 9000 series of quality management standards have now been published as Draft International Standards. Later this year the 1994 editions of ISO 9001, ISO 9002 and ISO 9003 will be with replaced by a single new standard - ISO 9001:2000. More details are given on the International Organization for Standardization, and the British Standards Institution web sites.
Last June we covered recruitment and employment sites in the scientific and engineering sectors. What we didn't mention, though, was salary information. Here are a selection of free salary surveys you may find useful.
Homefair - not a salary survey but a useful tool for calculating the equivalent rate of pay, taking into account the cost of living, from one city to another. International: most countries are represented.
Graduating Engineer Online - Covers USA - Average entry level salaries for graduates with engineering and computer degrees - 1999

Do you have a question, comment or suggestion on this newsletter? E-mail the editor - Jill - at [email protected] or fill in this form.

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