Monitor - ISSN 1472-0221
The Newsletter for Data Acquisition and Control
Issue 281 April 2022

Welcome to Monitor, thanks for subscribing. This month, how accurate are your temperature measurmements.

You can download a pdf copy of the newsletter here.

Contents

* How Accurate are your Temperature Measurements?
* From one of our Users
* Data Acquisition News Round-Up

How Accurate are your Temperature Measurements?

Web link: https://www.windmill.co.uk/thermocouple-accuracy.html

Thermocouples are commonly used to monitor temperature, but how accurate are the results?

Absolute Accuracy

There are many factors that limit the accuracy of the final figure for the temperature. Absolute Accuracy relates to how closely the thermocouple derived temperature mimics the actual temperature. The major errors usually arise from the thermocouple materials themselves.

There are international standards that specify the amount by which sensors may deviate from ideal behaviour, reproduced below.

Typically thermocouples are accurate to 1-2 degrees Celsius. As thermocouples age their chemical and electro properties change, reducing their accuracy. This effect is quicker in harsh environments and when you regularly heat and cool the thermocouple to the limits of its range.

Relative Accuracy

Relative Accuracy relates to measurement of changes in temperature, which is often the real purpose of thermocouples. Here the effect of noise can be very important. This happens when the thermocouple leads act as aerials picking up environmental electrical activity. A lot of this is common to both signal wires and a differential amplifier will remove a lot of 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, and as far away from electrical machinery as possible, will help. It's good practice to place the data acquisition units as close to the thermocouples as possible. Distributed systems using, for example, RS485, Ethernet or Modbus networks allow you to do this.

External Isothermal Box with Cold Junction Measurement

Thermocouple measurements depends on knowing the temperature of one of the junctions. Housing this junction externally in an isothermal box with a cold junction sensor will minimise junction errors and increase accuracy compared to having the reference junction inside the data logger.

Isothermal box connected to a Microlink 851-TC data logger

More Information

• Temperature Measurement with Thermocouples and RTDs
• Thermocouple and voltage data logger with digital I/O and counting
• 7 Ways to reduce noise

Or contact us for more information on measuring temperatures with thermocouples.

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From one of our users

"I use the software Windmill to receive and log the digital data read from the measurement sensors in the data acquisition unit of the laboratory experimental set-up designed for the still ongoing scientific research project titled as Laboratory Modeling of Proppant Transport and Settlement through Rough Transparent Artificial and Natural Fracture Replicas in the Example of Tight Sandstone and Gas Shale Unconventional Reservoirs of Thrace Region.

I am grateful to Windmill Software (Manchester, UK) for this state-of-the-art software and also to Lu Lu at Windmill for her valuable help and support."

Kayhan Develi, Assistant Professor at Istanbul Technical University

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 follow us on Twitter - @DataAcquisition - or grab our rss feed.

New solar panels work at night

Harvesting energy from the temperature difference between solar panels and surrounding air provides a renewable source of electricity at night. The system can be used as a continuous power source for both day and night in off-grid locations.
Source: Eureka Alert
https://www.eurekalert.org/

Researchers design vertical colour sensors

Another step towards developing an electronic eye.
Source: Georgia State University
https://news.gsu.edu/

New sensors harness the power of movement

Researchers have developed a sensor capable of using human movements - such as bending, twisting and stretching - to power wearable technology devices.
Source: Northumbria University
https://newsroom.northumbria.ac.uk/

Harmful chips hidden on circuit boards revealed by their power use

Careful observation of the power consumption of a circuit board can reveal telltale signs that an attacker has tampered with it and installed a malicious device designed to steal sensitive information or cause crashes, say researchers.
Source: New Scientist
https://www.newscientist.com/

Undersea detector proves it's swell

Highly energetic particles called muons are ever present in the atmosphere and pass through even massive objects with ease. Sensitive detectors installed along the Tokyo Bay tunnel measure muons passing through the sea above them, and can alert to tsunami waves
Source: University of Tokyo,
https://www.u-tokyo.ac.jp/

Multiplexing Could Give Neural Networks a Big Boost

Just as multiplexing can help a single communication channel carry many signals at the same time, a new study reveals that multiplexing can help neural networks scan dozens of streams of data simultaneously, letting them greatly boost the rate at which they analyze information.
Source: IEEE
https://spectrum.ieee.org/

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