Windmill Software Ltd
Windows Engineering Software

Monitor Archive

Home
Newsletters
Catalogue
Contents
Search

-------------------------Monitor------------------------
The Newsletter for PC-Based Data Acquisition and Control
Issue 92          www.windmill.co.uk          March 2006
--------------------ISSN 1472-0221----------------------

Welcome to Issue 92 of Monitor.  This month we give 
tips on using your PC to measure pH.  Should you wish to 
cancel your subscription to Monitor you can do so at 
http://www.windmill.co.uk/newsletter.html

CONTENTS
========
* Windmill News: Data Acquisition Glossary Updated
* How to Use a Computer to Measure pH
* DAQ News Roundup
________________________________________________________
________________________________________________________

Windmill News: Data Acquisition Glossary Updated
________________________________________________________

Thanks to readers pointing out terms we had missed, 
we have been able to further expand our glossary of 
data acquisition and control terms.  With links to 
further information and in-depth articles.
http://www.windmill.co.uk/glossary.html
________________________________________________________
________________________________________________________

How to Use a Computer to Measure pH
________________________________________________________

pH is measured in many industries, including nearly all 
handling water.  In fabric dyeing the permanence of the 
colour and the speed of the process depend on pH.  pH 
determines product quality in paper mills.  A change in 
pH in a lake or river is an early indicator of 
pollution.  And the correct pH is essential to ensure 
proper beer production.

What is pH?
===========

pH indicates the acidity of a solution.  The term "pH" 
was first used by W. M. Clark in 1920.  Previously the 
Danish biochemist Sorenson had used the term PH - H 
being a subscript of P.  The H stands for hydrogen. 
(An acid forms hydrogen ions in solution.)  It's unclear 
where the p came from.  It's often said that the p 
refers to the German word protenz, which apparently 
means power. This makes sense because the pH scale 
is a logarithmic one, so the p would refer to the 
power or exponent of 10.  However, in that case why 
was the German word for hydrogen not used? Jens Norby 
published a paper in 2000 arguing that the little p 
was simply a constant (Trends in Biochemical 
Sciences 25 (1) (2000) pp. 36-37.)

pH Sensors
==========

Various methods of measuring pH are available, but 
the most common one used in laboratory and industry 
is the glass electrode method. 

In this, the pH of a known reference solution is 
compared to the pH being measured.  Two electrodes 
are used: a glass measurement electrode and a 
reference electrode.

The measurement electrode comprises a glass bulb 
attached to a glass stem.  The bulb is a pH sensitive 
membrane filled with a conducting buffer solution. 
A silver wire is enclosed in the glass.  

The difference in pH between the solutions inside 
and outside the thin glass membrane creates an 
electrochemical force (voltage) proportional to 
the difference in pH. This is passed via the 
silver wire.

The reference electrode has a stable potential 
and also features a silver wire, enabling a 
complete circuit to be made and the voltage 
generated by the glass electrode to be measured.

The measurement and reference electrode may be 
individual and separate, or may be combined 
into one probe.  (There may also be a temperature 
compensating electrode.)  Individual electrodes 
are less practical than a combined probe, but 
may be more precise.

The probe may be connected to a pH meter that 
displays the current pH reading. 

How to Get pH Measurements into a Computer
==========================================

- pH Meter -

First let's take the case of a pH meter - a 
measuring device which displays the pH of 
the sample.  This will often have an RS232 or 
USB interface.  This means that you can connect 
it to the serial COM or USB port on 
your computer.  

You will also need some software to collect 
the data from the pH meter.  Software like 
the Windmill 6 COMIML program which reads 
data from the PC's RS232 COM port 
(http://www.windmill.co.uk/comiml.html).  
Those on a low budget could alternatively 
use the Windmill 4.3 software, which we 
offer free to all Monitor subscribers .

The Windmill software regularly collects 
the pH readings, every 5 seconds say, and 
saves them on the computer's hard disk.  
Windmill can also show live charts of the 
data, pass data in real-time to other 
programs like Excel and collect pH data 
alongside other data such as temperature 
or flow rate.

- pH Electrodes -

What if you are not using a pH meter but 
instead wish to connect the pH electrodes 
to the PC?  To do this you need a data 
acquisition (DAQ) device.  This device 
may be a card that you plug into the PC.  
More commonly, it is a unit sitting between 
the electrodes and the computer, connected 
to one of the PC's communication ports: 
USB, RS232, Ethernet or RS485 for example.  
You connect the electrodes to the DAQ device.  
The device then regularly takes pH readings 
and passes them to the computer.

pH electrodes have a very high output impedance 
and you cannot just connect them to a normal 
voltage input on your data acquisition unit.  
You will need instead to choose a DAQ unit that 
will amplify the signal to the appropriate level.  
For example, the Microlink 3000 system from 
Biodata Ltd comprises a frame of modules.  Each 
module is dedicated to a specific task: voltage 
input, counting, current output and so on.  It 
has a special module dedicated to pH signal 
conditioning that you slot into the frame. You 
connect the electrodes to this module.   You 
then connect the pH module to the normal 
voltage measuring module and take pH readings 
at the same time as other measurements.

Similarly, Biodata's small, portable, 
Microlink 751 unit - which plugs into the 
PC's USB port - has its own pH conditioning 
unit.

DAQ devices designed for pH measurement need 
input protected sockets to which you connect 
the electrodes.  As pH readings change 
relatively slowly, if possible you should 
choose an integrating analogue-to-digital 
converter as this reduces noise interference.  
These typically offer maximum sampling speeds 
of around 40 readings per second.

Further Reading
===============

More on Windmill Software...
http://www.windmill.co.uk/windmill.html
http://www.windmill.co.uk/comiml.html

Example pH Monitoring Applications...
http://www.windmill.co.uk/oil.html
http://www.windmill.co.uk/fish.html

pH Data Acquisition Hardware...
http://www.microlink.co.uk/3800.html
http://www.microlink.co.uk/751.html
________________________________________________________
________________________________________________________

DAQ News Roundup
________________________________________________________

Welcome to our roundup of the latest findings in 
data acquisition and control.  

If you would like to receive news updates as they 
happen then grab our RSS newsfeed at 
http://www.windmillsoft.com/monitor.xml.  Read 
http://www.windmill.co.uk/newsfeed.html for 
information how.

EU-funded sensor network goes a step beyond RFID

   An EU-funded project is going a step beyond existing 
   radio frequency identification (RFID) systems by 
   developing a sensor network that will allow items 
   to communicate more information about their 
   surroundings.  The technology can be used with goods 
   or equipment to make them "smart".  Items such as 
   cartons of foods will be able to warn operators when 
   the storage limit in a warehouse is reached, if a 
   leak occurs or if one is placed in the wrong location.
   Source: CEE-foodindustry.com
   http://www.cee-foodindustry.com/

Internet Standards Gives Birth to a New Industry in Building Automation Systems

   The adoption of Internet Standards in the Building 
   Automation Systems (BAS) market is giving birth to 
   a new industry focusing on information management 
   and analysis.  According to the ARC Advisory Group, 
   the worldwide market for BAS is expected to grow at 
   nearly 5 percent over the next five years.  The 
   adoption of Internet communication standards in the 
   BAS market is further extending the concept of 
   smart buildings by allowing companies to create a 
   single repository for all facilities data so that 
   it can be easily retrieved and shared between all 
   applications and all organizations within an enterprise.
   Source: ARC Advisory Group
   http://www.arcweb.com/

IEC Try to Solve Environmental Regulation Muddle

    As regulations about the environment increase, so 
    life becomes more difficult for the electrical and 
    electronics industries because the amount of paperwork 
    increases in the form of green procurement surveys or 
    supply chain questionnaires.  The regulations are 
    often a list of what one may not do and too much of 
    this, with varying criteria, creates a real Tower of 
    Babel. How to resolve the problem? IEC (International 
    Electrotechnical Commission) thinks the answer is 
    a Material Declaration Standard used worldwide and 
    has started work on this.
    Source: IEC
    http://www.iec.ch/news_centre/
________________________________________________________
________________________________________________________

* 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 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: monitor@windmill.co.uk
http://www.windmill.co.uk/
http://www.windmillsoft.com/

Do you have a question, comment or suggestion on this 
newsletter? Fill in this form to contact the editor.

Comments:   
Name:     
Email:     

Subscribing

To receive Monitor every month please fill in your e-mail address below. We will not pass your address to any third parties, nor send you any unsolicited e-mail.