Windmill Software Ltd
Data Acquisition Intelligence

September 2008

The Newsletter for PC-Based Data Acquisition and Control
Issue 122     September 2008
--------------------ISSN 1472-0221----------------------

Welcome to Monitor.  I hope you enjoy the newsletter but 
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* Happy Birthday Monitor Newsletter
* Debugging Noisy Measuring Systems
* Custom Number Formats in Excel: A Postscript
* DAQ News Roundup

Happy Birthday Monitor Newsletter

It is now 10 years since we launched Monitor and we'd 
like to thank you all for subscribing and making the 
newsletter a success. Over the years your contributions 
and comments have pushed us in new directions and made 
sure that the newsletter has stayed relevant.  We even 
appreciate your criticisms - so please keep writing to 
us and we'll try to keep going for another 10 years.

Debugging Noisy Measuring Systems

Recently a customer contacted Windmill to see if we 
could help fix their pH monitoring system, which was 
showing fluctuating readings. They sent the system - a 
Microlink 751 USB with a pH connection box - to us to 
test.  Our tests, though, showed nothing wrong and we 
deduced that the data acquisition equipment was not 
the source of the problem.  pH monitoring systems are 
very sensitive and prone to interference.  Small 
current or voltage surges can cause large fluctuations 
in readings.

Here are some simple tests that you can follow to determine 
the cause of pH (or other) measurement problems. We've used 
the Microlink 751 hardware, from Biodata, as an example, 
but many of the tips also apply to other manufacturer's 
systems.  Work through the tests one-by-one, eliminating 
sources of error as you go.

1. Check that the data acquisition (DAQ) unit is working 
   properly. First remove other factors in the system that 
   might be causing the problem, then check the 
   DAQ unit itself.

   a. Remove any power signal conditioner.  This provides 
      surge protection and noise filtering.  It should 
      remove interference from other equipment but a 
      faulty one could cause its own problems.

   b. Move the DAQ unit to another location. If you are 
      using it in a laboratory for example, take it home.

   c. Connect your DAQ unit to a different laptop running 
      on battery power, not on mains power.

   d. Now you can test whether the DAQ unit is the source 
      of the noisy, fluctuating, data.  Connect together 
      the first positive input pin, the first negative 
      input pin and the 0 V input pin. With the 
      Microlink 751 these inputs are on pins 20, 1 and 19. 
      You could use paperclips to connect the three pins. 
      Leave all other inputs unconnected. 

      As you have now shorted out the Microlink, if it is 
      working correctly it will produce a reading of zero. 
      If not the fault lies with the Microlink and you 
      should contact Technical Support and send the unit 
      back.  If the reading is zero then the problem is 
      very unlikely to be caused by the Microlink and you 
      can go on to step 2.

2. Once you have eliminated the DAQ unit as the source of 
   the fault, test the power supply to the computer.  Plug 
   the laptop into the mains - the reading should still 
   be zero. 

3. Reconnect any power signal conditioner. Again, check 
   that the reading is zero.

4. Test the probes one-by-one. Place a pH probe in a known 
   solution and see if the reading is as expected.  Keeping 
   the signal wires short and far away from electrical 
   machinery helps reduce noise. You may also need to 
   clean your electrodes.

5. Move everything back to the original location. If the 
   readings become erratic go through the tests again.

6. Disconnect from the laptop and connect to the original 
   computer. Again, if you now get noisy readings repeat 
   the tests. 

7. Finally make your measurements in a real situation.

Discovering at which stage the problem occurs will let you 
identify the source and take remedial action.

Further Reading:

Microlink 751 USB Unit

Monitor Issue 92, How to use a computer to measure pH

Monitor Issue 11, Differential v single-ended inputs

Custom Number Formats in Excel: A Postscript

Last month we published an article about ways to use 
Excel's custom number feature. (You can read this at 

In it we discussed how using the # symbol specifies 
rounding to a significant digit. For example, the custom 
format .## would cause 12.3456 to be shown as 12.35. 

One of our subscribers, Professor Chris van Zyl, pointed 
out that the 0 symbol has a similar function to the 
# symbol, but forces a zero if necessary. For example, 
the custom format:
#.##### would cause 0.3456 to be shown as .3456
0.##### would cause 0.3456 to be shown as 0.3456
0.####0 would cause 0.3456 to be shown as 0.34560

Thanks Chris for that addition.

DAQ News Roundup

Welcome to our roundup of the data acquisition and 
control news.  If you would like to receive more 
timely DAQ news updates then grab our RSS newsfeed 
at  Read for notes
on how to display the news on your own web site, 
read it via e-mail, mobile phone or in your browser.

Secrets of Effective Communication beneath the Sea
   If researchers can better understand how physical 
   conditions, like choppy seas and rocky bottoms, distort 
   sound as it travels through the ocean, they could send 
   data underwater faster and with less power and could 
   make it much easier for networks of sensors to talk 
   to each other simultaneously.  They could improve 
   wireless communications from ocean instruments 
   and potentially eliminate the need for vehicles 
   to surface just to transmit modest amounts of data.  
   With these goals in mind, a team led by Scripps 
   Institute of Oceanography has successfully 
   completed a three-week study.
   Source: SCUBA Diving News

Wireless Sensor Networks are a Good Investment
   According to new analysis from Frost and Sullivan, 
   wireless sensor networks now provide a demonstrable 
   return on investment.  As sensors become an integral 
   part of most industries, their high-volume applications 
   have increased their efficiencies of scale, thus in turn 
   lowering prices and promoting adoption in other devices.
   Source: Frost and Sullivan

Making Measurements Measure Up to Standards
   Information standards enable common activities. For 
   instance, bring your laptop anywhere in the world and 
   you will quickly and cheaply find a wireless Internet 
   connection - due to the globally adopted WiFi 
   standards. Researchers at the National Institute of 
   Standards and Technology (NIST) are working to enable 
   "WiFi-quality" information standards for manufacturing 
   metrology systems. In this pursuit, they have developed 
   DMIS which is a language for performing dimensional 
   measurements. DMIS allows measurement program 
   portability without requiring expensive translators.
   Source: NIST

Strong Showing for Industrial Controls
   Demand for industrial control equipment in the USA 
   improved during the second quarter, according to 
   NEMA's Primary Industrial Controls Index.  Manufacturing 
   activity, though not at the level of two years ago, 
   has remained resilient. 
   Source: Nema

Wireless sensors learn from life
   European and Indian researchers are applying 
   principles learned from living organisms to design 
   self-organising networks of wireless sensors 
   suitable for a wide range of environmental 
   monitoring purposes.  
   Source: ICT Results

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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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