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Engagement
  • Author Author: shabaz
  • Date Created: 12 Nov 2014 10:58 PM Date Created
  • Views 1026 views
  • Likes 7 likes
  • Comments 24 comments
  • logger
  • temperature
  • thermocouple
  • raspberry-pi
  • rpi
  • test_and_measurement
  • stem space
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Temperature Experiments with Thermocouples

shabaz
shabaz
12 Nov 2014

Introduction

It is one thing to check the temperature of something with a thermometer. However logging data and observing the change over time is a great way to see trends and gain more insight.

This blog post covers just a simple experiment but the aim is to have a more general solution for good quality temperature measurement, monitoring and logging at low cost.

 

What is needed?

A temperature sensor and logger is needed. Thanks to support from Element14 and element14Dave check out the blog post for a Raspberry Pi based temperature measurement solution. Of course, any temperature logging system could be used (e.g. off-the-shelf system, or an Arduino based solution mentioned in the comments section below).

 

Is it interesting?

In general, I believe so – perhaps if students are curious then they can measure anything within limits of hundreds of degrees C technically. Practically that would depend on their age and supervision.

 

As a suggestion for further discussion, maybe it could be turned into a game:  A challenge could be, "how long can one keep a drink hot", using nothing other than insulation or materials around the home/school and an hour of time? (by the way It turns out that the answer is: quite a long time. There is some more information on that later).

 

The challenge would involve researching parameters like thermal conductivity, area, and material thickness.

 

Variations of the challenge could involve guessing the temperature of an object at different times on a spreadsheet, and seeing who gets closest to the actual temperature curve – i.e. like a temperature based variation of battleships :  ) This could be automated of course.

image

As a first step, I tried an easier experiment to check out the performance of disposable cups – I wanted to know, is it really worth doubling-up on cups to keep a drink warm?

 

How to do it

First, get some water heated up (or use hot water from a tap).

 

Set up the temperature logging device and get it recording data. At this point the data is just recording room temperature.

 

Measure out an amount of the water into a cup placed in a tray or bowl (in case it leaks or is knocked over), and insert the temperature sensor.

 

I tried a paper cup (make sure it is intended for hot drinks) from the supermarket (Tesco in my case) with no lid, and measured for an hour. It didn’t keep the drink hot for very long. I used 200ml of water from a kettle. Room temperature was about 21 degrees C. I then repeated with a lid, and then a third experiment was with a doubled-up cup but still with one lid.

 

The conclusion (which I knew from experience since we have very similar cups at work!) is to drink quickly or always use a lid :-)

 

This is a very basic experiment of course, but it did help test out the Raspberry Pi temperature logger. The graph below shows the measured temperatures for an hour.

image

 

For the “how long can you keep a drink hot” challenge, here is my entry; I decided to use expanded polystyrene (Styrofoam) about 15mm thick sheets. I chopped it up using a piece of resistance wire connected up to a power supply. I used Nichrome wire of about 40 ohms/metre, and used 50cm of it connected to a 15V supply (outdoors in case the fumes were toxic) – this gently cuts, or turn up the voltage for a more aggressive cut : )

 

The pieces were glued using epoxy resin adhesive (Araldite) – other glues may damage the polystyrene. It was very tricky to get it absolutely watertight but eventually it was (a ready-made polystyrene cup would be an easier option, but my local supermarket didn’t have any : (

 

I also made a tight-fitting lid using expanded polystyrene. I again used 200ml of water, and started at around 51 degrees C, ambient temperature was 21 degrees C. Over the space of an hour, the temperature dropped by just under 8 degrees C. So that’s my record – looking forward to hearing if others can beat it (it shouldn't be hard : ).

image

 

To do the measurements, I used a temperature sensor known as a thermocouple, type ‘K’. It was an ‘exposed junction’ type, which isn’t really intended for liquids but is low cost – dry it thoroughly afterwards to prevent corrosion. Some thermocouple models have an exposed junction (such as the one in the photo below), others are enclosed in a probe where the end is either grounded to the probe or insulated, which affects response time.

 

Some of the enclosed models can handle over 1000 degrees C; others have insulation which functions up to about 250 degrees C, so it is worth checking before using it.

image

 

If you’re interested in building a thermocouple sensor solution for the RPI, check out the blog post here.

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Top Comments

  • Former Member
    Former Member over 8 years ago +2
    Interesting ideas for a class, I like it. I did something along this line some time ago when I made an Arduino data logger with 5 thermocouples & an LCD. I was looking at sample preservation/thermal stability…
  • shabaz
    shabaz over 8 years ago in reply to mikedavis +2
    The post has finally been updated with the code! It was difficult finding time to complete everything I wanted, but I figured I should post now, in case you or others also find time to help improve it…
  • timswift
    timswift over 8 years ago +1
    Could i use a arduino? Tim
  • shabaz
    shabaz over 8 years ago in reply to mikedavis

    The post has finally been updated with the code!

    It was difficult finding time to complete everything I wanted, but I figured I should post now, in case you or others also find time to help improve it.

    I think the same code could be used for multiple implementations, just replace the low-level code (in my case it is in a C file) with your code (could be C or Python etc), and then the Node.js code can be updated to (say) allow the actual implementation to be selected.

     

    The code is definitely just an experimental prototype, it does work, and certainly usable (I have already used it to log a few things) but has a few glitches (doesn't affect the logging or functionality) such as briefly displaying 0 degrees C if more than one user accesses the web page at the same time (currently I don't check to see if there are multiple users) - the problem does not exist during logging, then the correct value is always displayed for any number of users browsing it. The workaround for now was to just have one user accessing the page.

     

    Also, I've not quite finished the logging functionality - it does log, but I've not got round to implementing the 'stop log' button : ) So currently to stop logging one has to issue 'kill -9 xxx' at the CLI.

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  • toxxn
    toxxn over 8 years ago in reply to shabaz

    That may be true, I am sure there are many many more "egg experiments" out there.

     

    I would have to agree, I also regret not paying enough attention to those subjects. I also regret not participating in more elective classes pertaining to science or electronics. Although, I was not in such classes during my time in school except a basic computer class that was mandatory, which was more or less just a "learn to type on a keyboard" class, most everything I know related to science, electronics, computers, etc are all self-taught and through process of research and experimentation. I am a visual learner with ADHD, so self-teaching, i believe, is most effective for me to learn, by seeing and physically doing it myself.

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  • shabaz
    shabaz over 8 years ago in reply to toxxn

    Hehe I think teachers may have a "101 egg projects" book or something.

    I can think of some dull subjects that really were not fun too - although now I regret not paying enough attention to those subjects : (

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  • toxxn
    toxxn over 8 years ago in reply to shabaz

    You are most welcome. I cannot recall many "fun" spins on experiments back when I was in school. I mean, we just did some basic lab work and I recall only two experiments through all of my basic schooling that were what some might consider "fun". One was seeing how high we could drop an egg without it breaking using a variety of materials, and another was a demonstration of simple propulsion where we had to make a small model car and essentially see how far we could make it go without the use of motors or physically pushing it.

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  • shabaz
    shabaz over 8 years ago in reply to toxxn

    Hi Cory,

     

    Thanks for the comments! I'm now trying to recall any of the interesting things from school/university. One of the first things we had to do in computer lessons was draw an Xmas tree on the screen, and for microcontrollers it was to draw a castle on the oscilloscope, so it was getting there, but maybe teachers have more advanced psychological tricks to make things either relevant or fun. I think (or hope) a challenge type thing clicks with many people, in which case the types of experiments here could work. The group collaboration is a really good point, I had not thought of that!

    We used to have some fun summer projects like "how high can you place an egg with just 3 sheets of paper and sticky tape" which as you can imagine was a lot of fun in competitive groups.

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