Windmill Software Ltd
Windows Engineering Software

March 2005

The Newsletter for PC-Based Data Acquisition and Control
Issue 80          March 2005
--------------------ISSN 1472-0221----------------------

Welcome to our 80th issue.  We hope you find it 
useful, but should you wish to cancel your subscription 
to Monitor you can do so at

* Windmill News: ComDebug Helps Product Development
* Tensiometers and Computerised Irrigation
* Excel Corner: Average Values per Hour

Windmill News: ComDebug Helps Product Development

The Colour Vision Systems company manufactures fruit 
sorting equipment which is tailored specifically to a 
customer's needs.  When developing a new product they 
used ComDebug as a short-cut to understanding the control 
of Telemecanique Altivar variable speed drives. This 
helped them write dedicated drive communication software 
in-house, to control VSDs fitted to their machinery.

The ComDebug software they used has extensive 
trouble-shooting capabilities for communicating with 
almost any RS232, RS422, RS485 or Modbus serial device. 
What's more, it's free. Download your copy at

Further Reading:
Other Applications of Windmill
Colour Vision Systems

Tensiometers and Computerised Irrigation

Water management is very important in agriculture.  
Accurately monitoring soil moisture allows precise 
irrigation.  This maximises crop quality, reduces 
nutrient run-off and saves water.

One way to measure soil moisture is with a tensiometer.  
This comprises a sealed, water-filled, chamber with a 
porous ceramic tip; a vacuum gauge or pressure sensor; 
and, in a switching tensiometer, a contact relay.  The 
tensiometer senses and registers the suction force 
created by the plant pulling water from the soil.  When 
the soil is drying, water flows from the tensiometer 
chamber across the porous tip into the soil.  When the 
soil is re-wetted, the vacuum which was created inside 
the chamber during water removal pulls water back from 
the soil through the porous tip into the tensiometer.  
The tensiometer's pressure sensor registers the 
associated pressure changes.

A switching tensiometer can automatically control 
irrigation - not just sense soil moisture.  When the 
vacuum pressure in the chamber reaches a pre-set "dry" 
reading, a contact relay closes allowing irrigation.  
When the soil returns to the desired moisture level, 
the switch opens stopping irrigation.  Of course, the 
switch has to be connected to something.  For example, 
when the switch closes it might complete a circuit to 
a solenoid valve which opens and allows water to be 
applied to the soil.  Alternatively, you can use a 
PC to control irrigations.

With a PC and software like Windmill, you can also 
record all irrigations.  You can do this either by 
monitoring the state of the relay of a switching 
tensiometer, or by taking readings from the pressure 
transducer.  A new log file can be created each day or 
each week if necessary.  The data is easily imported 
into a database like Access or a spreadsheet like Excel.  
A computerised system can also record and display 
temperature, humidity, wind, rainfall and other data.  
Some tensiometers you can connect directly to the 
PC's COM port.  Others will need an interface fitted 
to the PC before you can take readings.  

Further Reading
Windmill COMIML: driver needed to communicate with the 

Windmill Logger

Excel Corner: Average Values per Hour

Assume you are continually logging data over several 
days, and importing the data into Excel.  You want to 
find out the average value for each hour.

Windmill collects data in this format

Time      Temp		
seconds   celsius
16:40:00  18.63
16:45:00  18.42
16:50:00  18.40
16:55:00  18.21
17:00:00  18.15
17:05:00  17.96
17:10:00  17.88
17:15:00  17.82
17:20:00  17.80

To find average readings each hour you need to:

1. Extract the hour from each time reading.  To do 
   this use =HOUR(A3), where A3 is the cell reference 
   of the first time stamp.  
   Place this formula in cell C3, then drag it down 
   to the bottom of the data table.
2. Create a named range called "Hour" for the values 
   in column C.
3. Create a named range called "Data" for the 
   data values.
4. Sum all temperatures for a specific hour.  For 
   example, for 4 o'clock use
   Place this in column D	
5. Count occurances of the specific hour with 
   Place this in column E
6. Divide the Sum by the Count to reach the average.
   For example, =D3/E3
   or, if you want to miss out columns D and E use
7. Repeat steps 4, 5 and 6 for the 23 other hour values.

Further Reading
For tips on using Excel with Windmill see
For tips on creating ranges in Excel 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]


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