Windmill Software Ltd
Windows Engineering Software

April 2005

The Newsletter for PC-Based Data Acquisition and Control
Issue 81          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

* 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
A more recent version of the software is available from

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
For more on Springfield Metallurgical Services see

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 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 
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

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

Further Reading
For tips on using Excel with Windmill see
For charting tips see
For tips on designing a user interface see

* 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]


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.


Previous Issue Next Issue