• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month
  1. 1
  2. 2
  3. 3
  4. 4
  5. 5
  6. 6
  7. 7
  8. 8
  9. 9
  10. 10
  11. 11

Experimenting with Thermocouples.

Extracts from this document...


                Page  of

Physics AS Level Coursework

Experimenting with Thermocouples


For my sensor coursework, I have chosen to investigate the properties of thermocouples.  A thermocouple is a sensor which detects a temperature difference, and produces a very small electrical output.

“In 1822, an Estonian physician named Thomas Seebeck discovered (accidentally) that the junction between two metals generates a voltage which is a function of temperature. Thermocouples rely on this Seebeck effect. Although almost any two types of metal can be used to make a thermocouple, a number of standard types are used because they possess predictable output voltages and large temperature gradients.”


Welding, or otherwise combining, two dissimilar metals can make a thermocouple. Varying the temperature of the junction where the two metals combine will produce a very small voltage and a very small current.





However, if one attempts to connect the thermocouple to a Voltmeter, another thermocouple junction is made. This is at the point of contact, where the ends of the thermocouples meet the contacts of the Voltmeter, and causes problems, as it can lead to errors in the result.  To compensate for this, a technique known as cold junction compensation (CJC) is used. This entails adding an extra wire of the first material at the end of the thermocouple, so that the metal in contact with the voltmeter are both made from the same material, which cancels out the potential difference.

A result of the CJC is that there are two free junctions.  One junction is kept at a constant temperature for the other junction to refer to.  That is why this junction is commonly known as the “reference” junction.  As most reference junctions are kept in an ice bath at a stable temperature of 0 o

...read more.


As thermocouples produce such a small current, a standard ammeter would not be inadequate.  A Moving-Coil Galvanometer is sensitive enough to measure the current accurately, and can be calibrated beforehand to get an accurate relationship between temperature difference of junctions and current produced. Ideally a digital Galvanometer would be used for improved accuracy.


This is the safest method of heating up water, compared to using a Bunsen burner (open flame hazard).  It is also cheaper than using a water bath, although unlike its more advanced counterpart, it cannot maintain a user-defined temperature.

Polystyrene beakers

These are safer to use than glass/Pyrex beakers, as polystyrene is a good insulator, reducing the chance of injury from handling the beakers, which contain hot substances.  Being a good insulator also reduces the rate at which the ice will melt, so I can continue the experiment for longer.  One polystyrene beaker will be used to contain the hot water for the “hot junction”, while the other will contain the ice for the “cold junction”.

Mercury Thermometer

The basic instrument for measuring the temperature of the water.  Cheap but reliable and accurate, the thermometer must be read at eye level for accuracy. Can operate between 0 oC and 100 oC, well within my parameters for my experiment.  Ideally a digital thermometer would be used for greater accuracy.

Crushed Ice

This has two purposes.  Firstly, it is required to construct an ice bath for the “cold” reference junction.  Secondly, it can be used as a coolant if the water is taking to long to cool by itself, a situation which can occur if the ambient room temperature is higher than average.  Being crushed gives the ice a larger surface area, which allows a larger surface area of the thermocouple junction to remain in contact.

Water Supply

...read more.


A practical example for use of a thermocouple is in an old style boiler.  When the pilot light (essentially a flame) is turned on, it heats up one junction of the thermocouple. This produces a small current, which is used as feedback to keep the pilot light alight.

From my experiments, I can see that there are some drawbacks, however.  In Copper-Constantan thermocouples, the smallest temperature change that can be sensed is 1 oC.  In some precision measuring applications in industry, this may simply be not accurate enough for the task at hand, such as monitoring a sick person’s body temperature in a hospital, for example, as this would deal in looking at changes in temperature in 0.1 oC.  

Also, it appears that a rapidly changing temperature would cause problems.


http://www.picotech.com/applications/thermocouple.html - A company specialising in the manufacture, research and development of a wide range of thermocouples.

http://www.madsci.org/posts/archives/oct99/939333814.Ph.r.html - An excellent overview of thermocouple theory on the atomic level.

http://www.its.org - The International Thermoelectric Society, a vast resource of information on all thermoelectric effects, which included thermocouple theory.

http://www.engineeringtoolbox.com/32_496.html - A general, all purpose website outlining various types of thermocouples, uses and operating ranges.

Advanced Level Practical Physics: Fourth Edition by M. Nelkon and J.M Ogborn – A source of ideas for experiments involving thermocouples.

Heinmann Advanced Science: Physics by Patrick Fullick – General listing of common sensors along with advantages and disadvantages of thermocouples.

Physics Tutor for advice on experiments and technical support.

[1] Ideally I would measure the temperature in Kelvin, starting from absolute zero. Unfortunately, this is impossible to recreate in a school lab environment.

[2] The junction which is in the area where the temperature has to be determined, i.e. the junction actually ‘measuring’ the temperature.

[3] Also known as the “reference junction”, this junction remains at a fixed temperature, usually 0 oC.

...read more.

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Electrical & Thermal Physics essays

  1. Thermistor Coursework

    I have worked out that when I use a 1000? thermistor (value of resistance of thermistor at 25°C) the fixed resistance that should give me the greatest range of potential difference output is as follows: I know that the resistance of the thermistor that I am using at 20°C is 1200 ?

  2. Using an LDR to detect the intensity of plane polarised light allowed through a ...

    How was my circuitry affected by systematic drift? Despite there being small fluctuations in my preliminary readings from the start to the end of my coursework, I do not feel this is significant as it is no greater than the fluctuations within the readings themselves.

  1. I am going to investigate what the resistivity is of a pencil lead. ...

    This also means that the difference in the voltage over the difference in the current equals the resistance - due to the formula R=V/I. 6. Once I have worked out the resistance I can then work out the resistivity of the pencil lead by putting it into the resistivity equation (above).

  2. Investigating the effect of 'length' on the resistance of a wire

    The voltage is the energy change (or potential difference) between the beginning and the end of wire, so the voltage increased with a decrease in current because as the length of the wire increases, more volts will be lost. ~Evaluating Evidence~ I came to the conclusion after carrying out the

  1. The aim of my investigation is to determine the specific heat capacity of aluminium.

    repeat the experiment starting at room temperature performing the experiment for only five minutes with the power pack on and then a further five minutes with the power-pack and hence heating filament off. I decided to record the change in temperature for a shorter length of time, to see whether

  2. physics sensor coursework

    My final design of circuit: A safety issue to be considered is not to have too high a voltage setting on the power supply. If there is a high voltage of about 10V and there is a low resistance component in the circuit, then the component may heat up and there is the risk of a fire.

  1. The electrolysis of copper from copper sulphate solution

    The reason being, that I do not want any of the solution spilling on to the electrical equipment, as this may have serious consequences attached to it. 4. Since copper sulphate is an irritant, I will have to be extra careful just to keep all the solutions within their containers.

  2. Physics coursework

    Also I will try and conduct them under the same room temperature as the slightest of alteration could affect my results considerably. I will conduct repeats in order to make my results more reliable. I will leave the thermistor in the certain degrees of water for the same amount of

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work