Windmill Software Ltd
Data Acquisition Intelligence

free driver
28 October 2000

     The Newsletter for PC-Based Data Acquisition and Control    
Issue 27                 October 2000
-------------------------ISSN 1472-0221--------------------------

Welcome to another edition of Monitor from Windmill Software. 

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* Windmill News: Any driver now free with Windmill
* Engineering Units
  - History of the different systems of units
  - Style conventions and rules for using SI Units
  - Why are SI Units the global choice?
* Exhibitions and conferences


                         Windmill News:                          
               Any Driver now Free with Windmill                

The Windmill data acquisition software suite works with a wide 
range of hardware, and thus has a series of hardware drivers. 
These include:
- the LabIML driver, which handles most instruments with an RS232 
- the Modbus drivers, which handle Modbus devices over RS232 or 
- the Harvester driver, which handles Fieldbus networks etc 
  acting as DDE servers

Previously Windmill was supplied with the LabIML driver and other 
drivers were extra. Now, though, our on-line catalogue lets you 
choose any driver when you buy Windmill.

You are not limited to one driver, however. You can connect many 
different types of hardware and simply buy the requisite drivers 
as the need arises. We've listed more drivers in our catalogue so 
it's easy for you to upgrade your system. For details see

      Engineering Units: SI, Metric, Imperial and American       

Just over a year ago, the Mars Climate Orbiter crashed into the 
surface of Mars. The main reason was a discrepancy over the units 
used. The navigation software expected data in newton second; the 
company who built the orbiter provided data in pound-force 
seconds. Another, less expensive, disappointment occurs when 
people used to British pints order a pint in the USA, only to be 
served what they consider a short measure. Again the reason is 
confusion over units; this time due to the fact that American 
units, although bearing the same names as British Imperial units, 
often refer to very different measures.

Why are there different systems of units?
In 1824 a British Act of Parliament gave precise definitions to 
Imperial units. These included the yard, pound, bushel and 
gallon. Six years later an American survey found weights and 
measures in various ports differed significantly. This led to the 
United States, in 1834, standardising measurements. However, 
although these were named after British units, they were not 
always the same measures as those used in Britain. The gallon 
chosen, for example, was the "Queen Anne wine gallon", which was 
already obsolete in Britain.

The most widely used system of units and measures around the 
world is the Systeme International d'Unites (SI), the modern form 
of the metric system. This originated in France, where in 1790 
the French Academy of Science was commissioned to design a new 
system of units. They decided that:
- The units should be based on unvarying quantities in nature
- Multiples of units should be decimal
- The base units should be used to derive other units
These principles allowed the metric system to evolve and SI units 
have become the fundamental basis of scientific measurement 


SI Base Units
There are just 7 base units

Quantity             Unit       Symbol

length               metre      m
mass                 kilogram   kg
time                 second     s
temperature          kelvin     K
amount of substance  mole       mol
electric current     ampere     A
luminous intensity   candela    cd

Prefixes are used to indicate powers of ten. They mean that with 
only one unit of measurement you can express any measurement from 
the smallest to the largest. They each have a short name and 
symbol. Large factors have upper case symbols, and small factors 
lower case symbols.

For example:
giga   1 000 000 000  G
mega   1 000 000      M
kilo   1 000          k
milli  0.001          m
micro  0.000 001      µ

Style Conventions and Rules for using SI Units
General principles for the writing of unit symbols and numbers 
were first proposed in 1948. These were subsequently adopted and 
elaborated by ISO, the international standards organisation.

1. Unit symbols are printed in roman (upright) type, irrespective 
   of how the rest of the text is printed.
2. Unit symbols are unaltered in the plural.
3. Unit symbols are written without a final full stop (period) 
   except for normal punctuation such as at the end of a 
4. Unit symbols are placed after the numerical value, leaving a 
   space between the value and the symbol. For example 5 V not 
5. Unit symbols are generally written in lower case letters, 
   except when the name of the unit is derived from a proper 
   name. (Note that when the name of a unit which is derived from 
   a proper name is written out in full, such as ampere or herz, 
   the name is not capitalised. The only exception to this is 
6. The the given SI unit symbol should be used. The symbol for 
   second, for example, is s. To use sec or secs is incorrect. 
7. Unit symbols and unit names shouldn't be mixed. Metre per 
   second, not metre/second or metre/s.

Summary of Advantages of SI Units: Why they are the Global Choice
- No conversions: only one unit for each quantity
- No numbers to memorise: derived units are defined algebraically 
  with no numerical factors
- No long rows of zeros: prefixes are used to indicate powers of 
- World standard: all other units, including British Imperial and 
  American units, are defined by them
- Not static but evolves to take advantage of increasing accuracy 
  of measurement standards and increasing needs for measurements


Further Reading
You can find more information on units on these web sites.

National Physical Laboratory (UK)

NIST: National Institute of Standards and Technology (USA)

Bureau International des Poids et Mesures

The Metric System [SI]: A concise reference guide

Metric Units and Conversion Charts, T Wildi, 1996, IEEE Press.

                   Exhibitions and Conferences                   
Every other month we list forthcoming exhibitions and conferences 
related to data acquisition and control.

1-2 November
NEMEX, National Energy Management Exhibition
NEC Birmingham UK
Europe's energy managing conference and exhibition. Features 
energy saving solutions, climate change levy debate and a series 
of workshops.

7-9 November
Manufacturing Week 2000
NEC Birmingham UK
As well as incorporating the Design Engineering Show and Vehicle 
Engineering & Design, this year's Manufacturing Week also 
includes Automation and  Production. Over 300 exhibitors plan to 

7-9 November
CIM 2000
NEC Birmingham UK
Computers in Manufacturing. A UK exhibition showing the latest IT 

7-11 November
Milan Italy
International exhibition for the automation, industrial 
components and instrumentation sectors. It boasts 2,600 
exhibiting companies coming from 30 countries, and an estimated 
60,000 visitors coming from around seventy countries.

21-22 November
Instrumentation South East
ExCel London UK

5-10 November
2000 International Mechanical Engineering Congress and Exposition 
Walt Disney World Florida USA
The congress aims to provide a program that balances academic, 
research and industrial applications. For design, manufacturing 
and product engineers.

28-30 November
Exhibition for automation technology. Exhibits include: data 
acquisition equipment, sensors and periphery equipment.

* Copyright Windmill Software Ltd
* Reprinting permitted with this notice included
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or publication, providing the above notice is 
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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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