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August 2002

Windmill Software Ltd
Data Acquisition Intelligence
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The Newsletter for PC-Based Data Acquisition and Control
Issue 49         August 2002
--------------------ISSN 1472-0221----------------------

Welcome to the August edition of Monitor. This month 
it's our fourth birthday and we now have almost 20 000 
subscribers - many thanks to you all. Today we're very 
pleased to bring news of how Windmill software 
played a key part in a coral-reef conservation study 
recently published in Hydrobiologia. We also highlight 
things to think about when choosing hardware to measure 

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* Windmill News: Windmill Software is Cornerstone of 
  Scientific Paper
* Monitoring Voltage Signals - Considerations when 
  Choosing DAQ Hardware
* Exhibitions

Windmill News: Windmill Software is Cornerstone of 
Scientific Paper

A paper recently published in the scientific journal 
Hydrobiologia, tells how the free Windmill software suite 
enabled marine biologists to devise a low-cost,  high-
performance procedure for automatic seafloor mapping. 
This has particular relevance for coral reef conservation 
in developing nations, as a snapshot of coral condition 
at the current time can be mapped. However, the method 
is also useful for aquaculture, salvage, SCUBA diving, 
fishing and other marine biology applications.

Previously accurate seafloor mapping and classification 
was an expensive undertaking requiring sophisticated 
equipment. This excluded low-budget groups in developing 
nations. In this study the scientists used our free 
software, an old 486 PC, an inexpensive echo sounder 
and gps receiver. They used simple synchronisation 
techniques to integrate videoed environmental data. 
From a small boat they mapped a Malaysian coral-reef 
area of 114 hectares in 6 hours, matching rates that 
up until now had only been achieved with air-borne 
imaging devices. However, improving on existing methods 
Windmill software allowed "ground-truthed" data that 
can be classified according to many schemes by direct 
observation of the habitat. It also provides detailed 
depth data that satellite imaging or air-borne 
spectrographic sensors do not provide.

The study concluded that the seafloor and coral reef 
mapping methodology described is so cheap that it is 
available to individual scientists in developing nations. 
As far as is known it is at the moment the only procedure 
that offers low-budget scientists a financially viable 
option for rapid mapping of both bathymetry and habitat 
characteristics of reef habitats on scales up to hundreds 
of square kilometres. As such, it is anticipated that 
this methodology may play a significant role in reef 
conservation efforts in developing nations.

More Details
To read the entire paper see:
A low-cost procedure for automatic seafloor mapping, with 
particular reference to coral reef conservation in 
developing nations
Hydrobiologia 474(1): 67-79; Apr 2002 
Trond-Inge Kvernevik; Mohd Zambri Mohd Akhir; Jill 

For details of the free software used, and step-by-step 
instructions, see

Monitoring Voltage Signals: Considerations when Choosing 
DAQ Hardware

Many sensors (the pieces of kit that detect physical 
parameters like temperature, strain or pressure) produce 
voltage signals. In fact, voltage is the signal most 
commonly interfaced by a computerised data acquisition 
and control (DAQ) system. Before the computer can process 
and store the voltage reading, however, the DAQ interface 
will need to condition the signal - amplify or filter it 
for instance - and then convert it to a digital number 
which the computer can deal with.

When choosing an interface for voltage measurements, 
three important things to consider are amplitude, 
frequency and duration.


A data acquisition system's analogue-to-digital converter 
is often calibrated for input voltages in the range 0-10 
V. However, voltages from sensors such as thermocouples 
or strain gauge bridges may need to be amplified 1000 
times to make it to a 0-10 V signal. For these types of 
measurements in-built amplification is generally offered 
as standard, making the DAQ interface capable of directly 
handling low voltage inputs from a few millivolts to a 
few volts.

If your signal is smaller than a few millivolts, you may 
need to consider more specialised hardware. Alternatively 
you could amplify the signal before it reaches the DAQ 

If your signal is larger than the maximum accepted by the 
A-D converter you can divide the signal down using a 
resistor network.


Before making a decision on data acquisition hardware, 
consider the highest frequency that you want to record. 
This helps you decide the speed of the hardware you need, 
and any filtering requirements. Noise may be present at 
higher frequencies than those you are trying to log, and 
you will need to be aware of it. You can remove noise by 
filtering the signal before digitising it. (See Monitor 
Issue 8 for more on filtering.)

The highest frequency component of the signal determines 
how often you should read the input - in theory at least 
twice the highest component. However, you will need 10 to 
20 points in a cycle to get a reasonable picture of a 
sinusoid. If you have more than one input, but only one 
A-D converter, the overall sampling rate will need to go 
up in proportion to the number of inputs.

For slowly changing, essentially DC signals all that is 
necessary is to consider the minimum time for a 
significant change in the signal.


For how long do you want to sample the signal? If you are 
recording the data then the duration determines the 
storage required. This may be on computer disk or in the 
memory of the DAQ hardware. The format of the stored data 
will also affect the amount of storage space required.


Other Considerations
There are obviously many other things to consider when 
choosing data acquisition hardware: compatibility with 
existing systems, software support, cost, expandability, 
method of connection to the computer, and so on. We hope 
this article has pin-pointed the specifics of the voltage 
measurement part of the picture.


Further Reading
The Microlink Measurement and Control Systems Catalogue 
has notes on sampling voltage inputs. This is available 
free from Biodata Ltd at

Related Monitor Articles
Monitor Issue 3, Analogue Signals and Types of A-D 
Monitor Issue 8, Filtering
Monitor Issue 10, Specifying a Data Acquisition System


Exhibitions and Conferences

Continuing our bi-monthly listing of exhibitions and 
conferences related to data acquisition and control.

IEEE AutotestCon 2002
Huntsville Al USA 
Conference focusing on automated test and related 
technology for military, government and aerospace 

2-5 September
Bella Center Copenhagen Denmark
Fair and conference for laboratory equipment, measuring 
technology and process control.

Instrumentation Scotland and Offshore Systems
4-5 September
Aberdeen UK

ATDC 2002
12-14 September
Slavonski Brod, Croatia
A forum to exchange scientific, technology and 
manufacturing knowledge between Western Europe and 
Central and Eastern Europe. Topics include product 
development, production technologies, information 
technology, quality assurance and measurement.

Sensors Expo
23-26 September
World Trade Center Boston USA
Brings together the technologies that are shaping 
sensing, data acquisition, control and communications.

Wescon North America
24-26 September
Anaheim Convention Center California USA
Exhibition including test & measurement and hardware & 
software design. 

1-3 October
NEC Birmingham UK
Into its 36th year, Nepcon includes test, measurement 
and inspection equipment for the electronics industry.

ISA 2002
21-24 October
Chicago USA
Instrumentation, systems and automation conference and 
exhibition. Includes emerging technologies, keynote 
addresses and more than 30 specialised training courses.

Energy Efficiency Expo
22-24 October  
Olympia 2 London UK
Promoting energy management systems, metering and 
monitoring, building control and data management.

HET Instrument 2002
4-8 November
Jaarbeurs Utrecht Netherlands 
The event for industrial automation and laboratory 

12-15 November
Nice Acropolis France
Dedicated to navigation and positioning applications.

ISA South America
19-22 November
ITM EXPO Fairs & Convention Center São Paulo Brasil 
Features new technology, applications and products for 
instrumentation, systems and industrial automation.

BIAS 2002
19-23 November
Milan Trade Fair Italy
Thirtieth international automation, instrumentation and 
microelectronics conference and exhibition

IT & Automation 2002
26-28 November
Nurnberg Germany
This exhibition takes the view that the continuous flow 
of information - from sensor to boardroom - is turning 
into the crucial factor for success in 
production-oriented companies. It therefore features 
all things realated to this.

* Copyright Windmill Software Ltd
* Reprinting permitted with this notice included
* For more articles see

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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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