-----------------------------Monitor-----------------------------
The Newsletter for PC-Based Data Acquisition and Control
Issue 23 www.windmill.co.uk August 2000
-------------------------ISSN 1472-0221--------------------------
CONTENTS
* Replaying Data After Collection
* Weather Monitoring
* Acronyms and Other Abbreviations
_________________________________________________________________
WINDMILL NEWS
==============
Replay Charts of Data After Collection
You can now read about our Windmill Replay software, and
download its new Help file, from our web site.
Windmill Replay plays back logged data files graphically. It's
ideal for scrolling through long files looking for significant
events. You can fast forward through uneventful stretches, and
pause for a more detailed look when something catches your eye.
The Replay screen is split between a moving graph and a table of
data values. How much space is devoted to each is up to you.
When the graph is static, double-clicking a point on it will
highlight the relevant row in the table. Similarly double-
clicking a point on the table will show the corresponding points
on the graph.
You can choose:
* Which channels to display: four channels of data from one
instrument and four from another for example
* The colour of each channel's trace on the graph
* Direction of replay: forward or reverse
* Speed of replay: slow or fast
* Zoom area and magnification
* The area to print
* How many decimal places should be shown in the data table
* The split between graph and table
To use Replay you also need the Windmill suite of software to
collect the data in the first place. Monitor subscribers
can download this for free.
You can now buy Replay from our on-line catalogue. It costs 195 GB
pounds (around 315 Euros or 295 US Dollars).
____________________________________________________________
USING A PC TO MONITOR WEATHER
==============================
Throughout time we've been fascinated by the weather - studying
signs of change and making and acting on predictions. In the 15th
Century, Cardinal Nicholas da Cusa invented one of the first
weather instruments: a hygrometer to measure the moisture
content of the air. Today we can link modern instruments to
computers to reduce human error, automate record keeping and
control conditions should limits be crossed.
Many weather conditions may be measured, including temperature,
atmospheric pressure, rainfall, humidity, wind speed, wind
direction and solar energy. Local weather measurements are
extremely important to a wide range of professions, from
horticulturists to fire fighters.
What do you need to Create a Computerised Monitoring System?
------------------------------------------------------------
There are three components to a computerised system.
* The instruments and sensors used to measure the changing
conditions. These might include anemometers to measure wind
speed, hygrometers to measure humidity and rain gauges to
measure precipitation.
* An interface between these instruments and the computer. This
is a piece of hardware which reads the instruments and passes
the data to the computer in a format it can understand. An
interface might be a unit which plugs into the PC's USB port,
such as the Microlink 751 we sell in our on-line catalogue.
Some weather instruments you can plug directly into the
computer's serial port eliminating the need for another
interface.
* Software to:
- Record the weather data in the units of your choice
- Display the data on-screen
- Analyse the data
- Make data available around a network or over the internet
- Alert you when measurement thresholds are crossed (by
telephone for example)
- Generate reports
- Control instruments on specific conditions - starting a
heater when the temperature drops for example
We, of course, use Windmill software, which works with a wide
range of instruments and devices. There are also many
dedicated weather monitoring packages on the market.
(Windmill 4.3 is available free to Monitor subscribers.)
Weather Instruments to Monitor Rainfall and Wind Speed
------------------------------------------------------
There isn't room here to detail all the different weather
conditions which may be monitored, so we've chosen to discuss
rainfall and wind speed. We'll cover other variables in future
issues.
*
Monitoring Rainfall
Strictly speaking, we're not monitoring rainfall but
precipitation: all the water that falls and is deposited on the
earth including snow, sleet, hale and dew. Precipitation or
rainfall is a very important measure in many applications. For
example, it is the single most important meteorological factor
to track when predicting changes in mosquito abundance, and
hence the potential for virus transmission from mosquitoes to
humans and other animals. Horticulturists, on the other hand,
use rainfall information to efficiently schedule planting and
irrigation.
The simplest way of measuring precipitation is by a rain gauge.
This is a calibrated cylindrical container with a funnel of
standard diameter into which the rain falls. Each day at the
same time the amount of rain in the cylinder is manually read
and recorded. This type of rain gauge was first used by King
Sejong of Korea (Choson) in the 15th Century.
However, we want to automate measurements so we leap forward to
the 17th Century and Sir Christopher Wren's invention of the
tipping bucket rain gauge. A bucket is balanced in unstable
equilibrium about a horizontal axis and is divided into two
equal compartments. In its normal position it is tilted with one
side resting against a stop. The rain falls into the upper
compartment and when a certain amount has fallen the bucket
overbalances and tilts the opposite way. The rain is thus
emptied out. Knowing the volume of the bucket, a count of tips
lets you calculate the volume of rain that has fallen.
These days we record the movement of the bucket electronically,
using an optical or magnetic switch and a counter input on the
data acquisition interface. The software will automatically
calculate the rainfall over a given time (usually 24 hours). For
more details of counting, see Issue 7 of Monitor.
With a computerised system, of course, you are not limited to
daily totals and can also obtain hourly totals, or totals for
any period you choose. Software like Windmill will also plot the
data for you on a chart, together with other conditions like
wind speed or humidity.
You need to mount your rain gauge in an open location, high
enough off the ground to prevent splashing. As a rule of thumb,
the distance of any obstacle from the gauge should be at least
twice, and preferably four times, the height of the object.
*
Monitoring Wind Speed
Wind is the motion of the air over the surface of the earth. The
unequal heating of the Earth's surface by the sun results in areas
of high and low pressure, and wind is defined as the motion of air
from high to low atmospheric pressure in a horizontal plane.
The measurement of wind, or air flow, is called anemometry.
Knowing the current wind speed, for example, lets farmers know
when it is safe to spray crops and informs fire fighters of the
danger of fires spreading. Wind speed records are used to
satisfy legal requirements where there is a possibility of
harmful discharge into the atmosphere. Wind monitoring is also
used in many non-weather applications, for example in controlled
explosion monitoring.
In computerised wind speed systems, a cup anemometer is often
used. This normally consists of three or four cups mounted
symmetrically about a vertical axis. As the wind blows, the
force on the concave side of any cup is greater than that on
a convex side in a similar position, thus causing the cup wheel
to rotate. The speed at which the wheel rotates is solely
dependent on wind speed.
A small electrical generator can be linked to the cup wheel.
This generates an electromotive force (a voltage) which gives
an instantaneous speed of rotation. This is transmitted to the
computer through an analogue voltage input on the interface.
Alternatively, an electrical contact could be made every
revolution. This would give a series of pulses, the frequency of
which would indicate wind speed. In this case the computer
interface needs a counter input.
Another method of measuring wind speed is with a Doppler
anemometer, which measures the speed of sound. If the air
through which the sound is travelling is moving, the speed of
sound appears to vary. This instrument has no moving parts, and
so doesn't wear out. It allows up to around 10 readings per
second, a speed quick enough for monitoring air movement away
from explosions.
Proper siting of any anemometer is important to ensure accurate
readings. For example, wind sensors should not be installed to
close to a building, as turbulence created by the building can
interfere with readings.
Further Reading
Monitor Issue 7: Timing and Counting
More information on using a PC for counting applications like
rainfall and wind speed measurement.
Monitor Issue 6: Emission Monitoring
Discusses the monitoring of air pollutants
Monitor Issue 5: Temperature Measurement
Describes how to use your PC to measure temperatures.
Fire Fighters and Weather Screens
Explains how a fire station uses a computerised weather
monitoring system.
Mosquito Control Handbook: St. Louis Encephalitis. University of
Florida, Institute of Food and Agricultural Sciences
One example of how weather monitoring can help predict mosquito
abundance.
Abbas Ali Hussain, Interfacing Meteorological Instruments to a
Computer, MSc Thesis, Manchester Metropolitan University, UK
____________________________________________________________
DATA ACQUISITION AND CONTROL ABBREVIATIONS
====================================================
Continuing our acronym and other abbreviation reference guide.
For A-G see Issue 22 of Monitor
HART
Highway Addressable Remote Terminal
Provides digital communication to microprocessor-based (smart)
analogue process control instruments.
http://www.hartcomm.org/
HMI
Human Machine Interface
Also known as man machine interface. The communication between
the computer system and the people who use it.
https://www.windmill.co.uk/monitor9.html
HTML
Hyptertext Markup Language
A document language for the world wide web. It indicates the type
of information rather than the exact way it is to be presented
http://www.w3.org/MarkUp/
HTTP
Hyptertext Transfer Protocol
The set of rules for exchanging html documents between web
servers and browsers.
http://www.w3.org/Protocols/
I/O
Input/Output
A data acquisition system monitors signals through its inputs,
and sends control signals through its outputs.
IEEE
Institute of Electrical and Electronics Engineers.
An American Society that, amongst other things, establishes
international standards in the computing, electronic and
telecommunications fields.
http://www.ieee.org/
IML
Interface Management Language
A programming language used to communicate with measurement
instruments.
IR
Infrared
ISA
Instrument Society of America
The international society for measurement and control.
https://www.isa.org/
ISA
Industry Standard Architecture
An ISA expansion slot lets you plug data acquisition boards into
PCs. Other methods include the universal serial bus.
ISO
International Organization for Standardization
Made up of national members. A member is the "most representative
of standardisation in its country". For example BSI (British
Standards Institute), DIN (Deutsches Institut für Normung) and
ANSI (American National Standards Institute).
http://www.iso.ch/
ISP
Internet Service Provider
IT
Information Technology.
Covers all aspects of managing and processing information with a
computer.
LAN
Local area network.
A data communication system connecting devices in the same
vicinity. Data is transferred without the use of public
communications. Examples of LANs are Ethernet, token ring and
Modbus.
LASER
Light amplification by stimulated emission of radiation
http://www.achilles.net/~jtalbot/history/
LED
Light Emitting Diode
Used as indicator lights on electronic devices, including data
acquisition interfaces.
LIFO
Last in first out.
Describes a stack method of data storage.
LIMS
Laboratory information management system
LVDT
Linear Variable Differential Transformer
Used in measuring devices that need to convert changes in
physical position to an electrical output.
MES
Manufacturing Execution System
Delivers information about, and controls, plant activities.
MIS
Management Information System
http://www.misq.org/
MMI
Man Machine Interface.
Also known as human machine interface. The
communication between the computer system and the people who use it.
https://www.windmill.co.uk/monitor9.html
Next month: the final part of our data acquisition abbreviation
explanations.
____________________________________________________________
Do you have a question, comment or suggestion on this
newsletter? E-mail the editor - Jill - at monitor@windmillsoft.com
or fill in this form.
Copyright 2000 Windmill Software Ltd. All rights reserved.
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