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Data Acquisition Intelligence

RS-232 Interface
28 July 2000

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-----------------------------Monitor-----------------------------
     The Newsletter for PC-Based Data Acquisition and Control    
Issue 24               www.windmill.co.uk               July 2000
-------------------------ISSN 1472-0221--------------------------

Welcome to issue 24 of Monitor from Windmill Software. Today we 
are pleased to announce that Windmill is now available for 
USB data acquisition units! These plug into the computer's 
universal serial bus port. We discuss USB below, highlighting 
its benefits for measurement and control.

We only send this newsletter to people who have subscribed - 
should you wish to cancel your free subscription please visit 
http://www.windmill.co.uk/newsletter.html

CONTENTS
========
* Windmill News: New USB Unit Uses Windmill
* What is the universal serial bus?
* Data acquisition abbreviations explained

_________________________________________________________________

            Windmill News: New USB Unit Uses Windmill      

The new USB unit from Biodata takes full advantage of the 
Windmill software suite. Called the Microlink 751, the unit 
lets you:
* measure voltage, current, temperature and strain
* switch digital outputs
* monitor digital inputs
* count up to 65535

You simply plug the compact Microlink 751 into the computer's 
USB port - no need to switch off your PC or even restart 
Windows. With the powerful yet easy-to-use Windmill applications 
you can be logging, charting and counting in no time. To discover
just how easy it is, visit
https://www.windmillsoft.com/

The Microlink 751 and Windmill software package costs just 595 
British pounds (around 895 US dollars or 945 euros). This 
includes free technical support for life and a 
money back guarantee if not absolutely satisfied. For secure 
ordering go to 
https://www.windmillsoft.com/
_________________________________________________________________

                What is the Universal Serial Bus?                

The USB is a relatively recent way to connect instruments and 
devices to the PC. Most new computers have one or two USB ports, 
in addition to the familiar RS232 (COM) and parallel ports. You 
can use the USB ports to connect peripherals like digital 
cameras, printers and data acquisition and control units.

Why use the USB for Data Acquisition?
=====================================
The USB is extremely convenient for data acquisition for several 
reasons.
* The equipment can obtain power from the USB; it doesn't need to 
  be battery powered or plugged into the wall. This makes USB 
  ideal for portable data acquisition with a laptop.
* Using a USB hub you can connect many devices to one USB port - 
  letting you easily expand your system should requirements grow.
* USB ports are provided on most new PCs - no need to open the 
  computer and install adaptor cards.
* You can plug in and unplug your equipment without switching off 
  your computer or even restarting Windows.
* The USB cable can be up to 5 m long. However, using USB hubs 
  between cables you can reach 30m.
* Faster speeds than those allowed by RS232 connections are 
  achievable
* You can use USB devices alongside existing data acquisition 
  equipment (such as cards that you've installed in your PC or 
  instruments that plug directly into the RS232 port).

What about older PCs?
=====================
If your PC does not have a USB port you can buy a PCI-based card 
which provides one. However, you need to be running Windows 98 or 
Windows 2000. (Early releases of Windows 95 do not support USB, 
later releases have some support but it's better to use Windows 
98 or 2000.) You can test whether your PC is USB compatible by 
visiting www.usb.org and downloading their evaluation utility 
program.

If you don't wish to upgrade your machine there are many other 
ways to connect data acquisition equipment to computers, such as 
Ethernet, RS232, RS485, Modbus or GPIB. Issue 2 of Monitor - 
http://www.windmill.co.uk/freewm.html - discusses a range of 
methods.

Cable Details
=============
The USB cable should have an "A" plug at one end (for the 
computer) and a "B" plug at the other: no sockets. Any other 
arrangement doesn't conform to the standard. The cable comprises 
four wires: two carry your signal data and two supply voltage. 
The bus can operate at two different speeds, depending on the 
attached device. The device itself tells the bus what its speed 
is through the voltage cables. The cable should not be longer 
than 5 metres for fast devices, or 3 metres for slow devices. 
However, you can use up to 5 USB hubs to connect cables, giving a 
maximum distance of 30 m.

The Future for USB
==================
In April this year the USB 2.0 specification was released. This 
allows for faster data transfer of 480 megabits per second. 
However, the specification has been designed to be totally 
compatible with the existing USB standard. The new specification 
was developed by the USB Promoter Group, which includes Compaq, 
Intel, Microsoft and Philips Semiconductors. Future upgrades are 
promised to have equal compatibility, so you can be sure that as 
technology advances so will your data acquisition system.

Further Reading
===============
USB Implementers Forum
http://www.usb.org/

USB Complete, Axelson J, 1999. ISBN: 0965081931, Lakeview Research
More details at amazon.co.uk or amazon.com.

USB Explained, McDowell and Seyer, 1998. ISBN: 013081153X, 
Prentice Hall
More details at amazon.co.uk or amazon.com.
_________________________________________________________________

            Data Acquisition and Control Abbreviations           

Continuing our acronym and other abbreviation reference guide. 
For A-M see Issue 22 and 23 of Monitor
http://www.windmill.co.uk/monitor22.html
http://www.windmill.co.uk/monitor23.html

ODBC
Open database connectivity
Developed by Microsoft, a standard for accessing a database. By 
using ODBC statements in a program you can access files in a 
number of different databases, including Access, dBase and Text. 
In addition to the ODBC software, a separate module or driver is 
needed to access each database. 
http://www.microsoft.com/data/odbc/

OEM
Original Equipment Manufacturer
A company that makes basic hardware for other manufacturers to 
build into their products. 

OOP
Object-Orientated Programming
Languages using OOP include Visual Basic, Java and C++.
http://catalog.com/softinfo/objects.html

OS
Operating System
Examples include Windows, DOS and UNIX.

PC
Personal Computer
Generally applied to computers conforming to the IBM designed 
architecture.

PCB
Printed Circuit Board

PCI
Peripheral Component Interconnect
A local bus standard developed by in 1992. PCI cards plug into 
your computer and are configured through software. They do not 
have jumpers or switches.
http://www.pc.ibm.com/us/infobrf/ibpci.html

PCMCIA
Personal Computer Memory Card International Association
Industry group that developed the specification for credit card-
sized plug-in cards for laptop computers.
http://www.pc-card.com/

PD
Proportional Derivative
See PID

pH
potential of Hydrogen
A measure of acidity. At 25 C (77 F) a neutral solution such as 
pure water has a pH of 7; a pH of less than 7 indicates acidity, 
more than 7 alkalinity.

PI
Proportional Integral
See PID

PI&D
Piping and Instrumentation Diagram

PID
Proportional Integral Derivative
Proportional gain, integral action time and derivative action 
time. A feedback method for control. PID software, for example, 
compares an analogue input value with a set point and if there is 
a discrepancy outputs an appropriate analogue or digital control 
value, according the PID calculations. 

PID
Process and Instrumentation Design

PLC
Programmable Logic Controller
A microprocessor-based device used in industrial monitoring and 
control.

ppb
Parts Per Billion

ppm
Parts Per Million

ppt
Parts Per Thousand

PROFIBUS
Process Fieldbus
http://www.profibus.com/

PRT
Platinum Resistance Thermometer
A type of RTD (resistance temperature device) made of platinum. 
Has long term stability.

Pt100
A PRT specified to have a resistance of 100 ohm at 0 oC.

QA
Quality Assurance

QC
Quality Control

R&D
Research and Development

RF
Radio Frequency
Any frequency within the electromagnetic spectrum suitable for 
radio broadcasting and communications. Frequencies extend from 9 
kilohertz to thousands of gigahertz. The RF spectrum is divided 
into several bands, including VHF and UHF.

RFI
Radio Frequency Interference

rms
Root mean square
The square root of the sum of the squares of a set of quantities 
divided by the total number of quantities. Used when monitoring 
ac (alternating current) signals. Many power supplies, for 
example, issue an ac signal. This needs to be converted to a dc 
(direct current) signal for the PC interface. The solution is a 
signal conditioning input that produces a dc signal proportional 
to the rms of the amplitude of the input signal. The rms 
operation means the reading will always be positive.

RTD
Resistance Temperature Device or Resistance Thermometer Detector
Rely on the principle that the resistance of a metal increases 
with temperature. 
http://www.windmill.co.uk/thermocouple.html

RS232
Recommended Standard 232
A protocol for serial data communications. An RS232 link will run 
at up 38400 baud (bits per second) over short distances, and at 
lower speeds as the distance increases. You can plug the RS232 
lead directly into the computer's serial (COM) port. 


RS485
Recommended Standard 485
Another protocol for serial communications. Allows several 
devices to be connected to a single cable, distributed over a 
wide area.

SCADA
Supervisory Control and Data Acquisition

SCSI
Small Computer Standard Interface
SCSI is a parallel interface standard used by Apple Macintosh 
computers, PCs and many UNIX systems for attaching peripheral 
devices to computers.
http://www.hardwarecentral.com/hardwarecentral/print/36/

S/H 
Sample and Hold 
A component of a type of analogue-to-digital converter. The 
analogue signal is frozen in a sample and hold circuit to prevent 
it changing during digitisation.
http://www.windmill.co.uk/a-d.html

SE 
Single-Ended 
An analogue input that is measured with respect to a common 
earth. Single ended inputs are only suitable for signals that are 
of good size - 100 mV full scale or above.

SHTTP
Secure-Hypertext Transfer Protocol
An extension to the HTTP protocol to support sending data 
securely over the World Wide Web. 

SMTP
Simple Mail Transfer Protocol. 
The Internet standard protocol for transferring electronic mail 
messages from one computer to another. Regulates the 
communication between mail servers.

SI
International system of units. Abbreviation for Systeme 
International (d'Unites).

SP
Set Point
Value of a controlled variable, departure from which causes a 
controller to operate to reduce the error and restore the 
intended steady state. 

SPC
Statistical Process Control
A method to separate random variations in data from non-random 
variations. Used in automatic product testing.

SQL
Structured Query Language
A query language for requesting information from a database. The 
original SQL was introduced in 1979 by Oracle Corporation. 
Supports distributed databases, spread over several computer 
systems.

TCP/IP
Transmission Control Protocol/Internet Protocol
The communications language used between computers on the 
Internet. IP is the specification that determines where packets 
of information are routed to, based on their destination address. 
TCP makes sure that the packets arrive correctly at their 
destination address. If TCP determines that a packet was not 
received, it will try to resend the packet until it is received 
properly. 

TTL 
Transistor-Transistor Logic
Referring to logic circuits consisting of two or more directly 
interconnected transistors, to provide conditional switching 
capability. For digital input circuits, a logic 1 is obtained for 
inputs of 2.0 to 5.5 V which can source 40 microA, and a logic 0 
for inputs of 0 to 0.8 V which can sink 1.6 mA. For digital 
output signals, a logic 1 is represented by 2.4 to 5.5 V with a 
current source capability of at least 400 microA; and a logic 0 
by 0 to 0.6 V with a current sink capability of at least 16 mA. 

UHF
Ultra High Frequency
Radio waves between 300 MHz and 3000 MHz.

UPS
Uninterruptable Power Supply
Used to keep critical equipment, including computers, running in 
the event of a mains power failure. 

USB
Universal Serial Bus
A serial communications protocol for connecting peripherals to 
computers - is gradually replacing RS232 and parallel ports.

VHF
Very High Frequency
Radio waves between 30 MHz and 300 MHz.

WAN 
Wide area network. A network of circuits spanning a large region 
that is used to transmit data. 

XFMR
Transformer

Next month:
  It's Monitor's second birthday and we're including a complete 
  index of all subjects covered in our previous issues.

_________________________________________________________________

* Copyright Windmill Software Ltd
* Reprinting permitted with this notice included
* For more articles see http://www.windmill.co.uk

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 - including articles on temperature 
and strain measurement - is at 
http://www.windmill.co.uk/newsletter.html

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]
http://www.windmill.co.uk/
https://www.windmillsoft.com/


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