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22 August 2012

Windmill Software Ltd
Data Acquisition Intelligence

The Newsletter for PC-Based Data Acquisition and Control
Issue 169         August 2012
--------------------ISSN 1472-0221----------------------

All measurements are contaminated by noise - today we 
discuss how you can minimise its effects on your signals. 
We also pleased to announce that you can now buy the 
new Microlink thermocouple data logger from our 
web site.

I hope find the newsletter useful, but should you wish 
to remove yourself from our mailing please go to 
Monitor Newsletter

* Windmill News: Thermocouple Data Logger also Measures 
  Voltage, Flow, Level etc
* How to Remove Noise from your Measurements
* DAQ News Round-up

Follow @DataAcquisition on Twitter Google+ Data Acquisition News Feed (RSS)

Thermocouple Data Logger also Measures Voltage, 
Flow, Level, etc

851-TC Thermocouple Data Logger
The new Microlink themocouple 
data logger not only logs 
temperature data but 
can also measure voltage, 
flow, level etc.  Additionally, 
it provides digital I/O and 
event and frequency counting. 
Read on for more details or see

The Thermocouple Data Logger:

- Monitors 16 thermocouples or voltage signals
- Has built-in linearisation for B-, E-, J-, K-, N-, R-, S- 
  and T-type thermocouples
- Automatically detects broken thermocouple leads
- With extra hardware also measure strain, current and pH
- Reads data over an Ethernet network or over the Internet
- Reduces electrical noise with an integrating analogue-to-
  digital converter
- Lets you select the resolution of the A-D converter from 
  12- to 18-bits: choose high resolution or high speed
- Automatic recalibrates itself
- Offers two alarms on each input
- Lets you choose real-time data acquisition on your PC or 
  stand-alone data logging

Themocouple Measurement

The system comprises a Microlink 851 measurement unit, an 
isothermal box, Windmill data acquisition and control software 
and technical support for life.

You connect the thermocouple wires to screw terminals in the 
Microlink isothermal box. This keeps the temperature of the 
thermocouple junctions constant, measured by a cold junction 
sensor in the box. Plug the isothermal box into the 
Microlink 851 using its ribbon cable. The isothermal box will 
also detect broken thermocouple leads for you. For more 
information on monitoring thermocouples, see our tutorial on 
computerised themocouple measurement

Further Reading
More information on the 851-TC package:

How to make temperature measurements - pitfalls of 
monitoring thermocouples and RTDs:

How to Remove Noise from your Measurements 

All measurements are contaminated by noise. It may be 
generated within the electrical components of the 
input amplifier: called internal noise. It may also be 
added to the signal as it travels down the wires to 
the amplifier: called external noise.  Noise is more 
of a problem for millivolt signals, from sensors 
like thermocouples, than it is for larger, volt-level, 

How do you minimise the effect of noise on your signal?

Reducing Noise Generated by the Amplifier

  Internal noise arises from thermal effects in the 
  amplifier and although it can be minimised it cannot 
  be removed completely. (The amplifier in data acquisition 
  equipment increases the voltage signal to a level 
  suitable for the analogue-to-digital converter.) 

  Typically amplifiers will generate a few microvolts of 
  internal noise which limits the resolution of the 
  signal to this level. The amount of noise added to the 
  signal depends on the bandwidth of the input amplifier, 
  from the lowest frequency allowed into the amplifier 
  to the highest. Amplifiers with a bandwidth matching 
  that of the input signal will be less noisy than, say, 
  feeding a 100 Hz signal into an amplifier that covers 
  0 to 10 MHz. 

  Integrating A-D converters reduce noise by 
  integrating the signal over a period, which is 
  effectively reducing the bandwidth.

Reducing Environmental Noise

  External noise reduction is much more of an art form. 
  Noise is added because the signal leads act as aerials 
  picking up environmental electrical activity. Much of 
  this is common to both signal wires, and a differential 
  amplifier will remove a lot of this common mode voltage. 

  Differences between the signal wires (for example if 
  they are separated rather than twisted together) will 
  lead to residual voltages being added to the signal, 
  increasing noise. Keeping the signal wires as short 
  as possible, twisted together and as far away from 
  electrical machinery as possible, will help.  You can 
  also shield your signal wires.

Filtering Noise

  Filtering can reduces noise errors in the signal. 
  For most applications a low-pass filter is used. This 
  allows through the lower frequency components but 
  attenuates the higher frequencies. The cut-off 
  frequency must be compatible with the frequencies 
  present in the actual signal - as opposed to 
  possible contamination by noise - and the sampling 
  rate used for the A-D conversion.

  A low-pass filter that's used to prevent higher 
  frequencies, in either the signal or noise, from 
  introducing distortion into the digitised signal 
  is known as an anti-aliasing filter. These generally 
  have a sharper cut-off than the normal low-pass 
  filter used to condition a signal. Anti-aliasing 
  filters are specified according to the sampling 
  rate of the system and there must be one filter 
  per input signal.

  You can read more about filtering in Issue 8 
  of Monitor.

Summary of Reducing Noise

  - Keep the signal wires short
  - Keep the wires away from electrical machinery
  - Use twisted pair wires
  - Use differential inputs to remove noise common the both wires
  - Use an integrating A-D converter to reduce mains frequency interference
  - Filter the signal 
  - Consider shielding the wires

Further Reading

Monitor Issue 8: Filtering - Removing Interference from your Signal,

Monitor Issue 122: Debugging Noisy Measuring Systems,

Monitor Issue 155: Differential or Single-Ended Inputs?,

________________________________________________________ ________________________________________________________ DAQ News Round-up ________________________________________________________ Welcome to our round-up of the data acquisition and control news. If you would like to receive more timely DAQ news updates then either follow us on Twitter at!/DataAcquisition or grab our RSS newsfeed at NIST Releases Test Framework for Upgrading Smart Electrical Meters Next-generation 'smart' electrical meters for residential and commercial buildings will have computerised operating systems just as laptops or mobile devices do. Source: NIST Industrial PC Market Driven by Need for Data According to the Arc Advisory Group, the Industrial PC (IPC) market continues to grow faster than most other automation hardware markets as IPC-based automation solutions replace PLCs in traditional machine control applications. Growth is also driven by the preference for IPCs in comparably new and growing areas such as wind energy. Source: Arc Advisory Group ISA Charters New Standards Committee on Intelligent Device Management The International Society of Automation has established a new standards committee, ISA108, Intelligent Device Management. The committee will define standard templates of best practices and work processes for design, development, installation and use of diagnostic and other information provided by intelligent field devices in the process industries. Source: International Society of Automation Hairy sensors to give robots sensitive skin A coating of hairy, electronic skin could soon help robots feel the slightest breath of air. Source: New Scientist ________________________________________________________ ________________________________________________________ * Copyright Windmill Software Ltd * Reprinting permitted with this notice included * For more articles see 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 and an index of articles at 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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