How do I measure the resolution of a thermocouple.

Hi guys,

For my coursework I've been given the experiment of finding out the resolution of a thermocouple.

I already know how to setup the thermocouple etc. as I've been shown however I was just wondering if anyone knew what reading I should take and how to actually work out the resolution?

Cheers!

Firstly, are you clear what it is you are trying to measure; ie. what is meant by the "resolution" of the thermocouple? Is it the measurement sensitivity you are after?
Won't this depend on the instrument you are connecting to the thermocouple to measure the emf?

This is exactly what I'm confused about. They've handed out a booklet and inside my teachers define and discuss the resolution as:
"The resolution of an instrument is the smallest change that can be detected at the output.

The output of a digital instrument is a numerical display. The resolution is the smallest change of input the instrument can display. For example, a digital voltmeter that gives a three-digit read-out up to 1.35V has a resolution of 0.01V since the smallest change in p.d. it can display is 0.01V

For an analogue instrument, the output is the position of a pointer on a scale. Its resolution is the smallest change in input that can be detected as a movement of the pointer. The resolution of an analogue instrument can be improved using a magnifying lens to observe moment of the pointer."

It's definitely not the sensitivity since other people in my set have been given this experiment.

Basically I've been told to do "A careful study of one or more of the properties of a sensor or instrument: Resolution of a thermocouple" and I've been given 5 hours of lab time to do an experiment.

What kind of thing do you think I should measure - surely it also won't take me 5 hours? :/

OK so you seem clear what it is you are aiming to measure.
If you are using a voltmeter with a resolution of 0.01V then clearly the smallest change in emf it can measure is 0.01V
So what you need to do is find what change in temperature produces a change of 0.01V.
Correct?
You need to calibrate the thermocouple first.
Do you know how to do this?
If you do, it's half way to seeing what it is you need to do here.

Yes - I believe that's what I need to do

I can't remember how to calibrate I'm afraid, although I know I've definitely done it Is it where I record readings and then plot them onto a graph connecting the points so that I can read from the graph to give me the correct values?

You have to work out how to convert the voltage measurements to temperature using known values of temperature and measuring the emfs produced.
Yes a graph is useful.
I found one example experiment here but there are many on the web.
You need to look around and adapt to the setup you have.
http://www.calpoly.edu/~gthorncr/ME236/documents/Exp2.pdf

Thanks a lot for your help

What do you mean by converting the voltage measurements to temperature? Will the reading from the voltmeter be the emf? Sorry, i'm a little confused.

That's what calibration is all about.
You want to be able to pop one end of the thermocouple in, say, a cup of coffee and measure its temperature. All you get from voltmeter is a reading of so many millivolts.
So what is the temperature of the coffee, then? How do you know what temperature corresponds to the reading on the meter?
Calibrating means establishing how the emf you read (output) relates to the temperature you want to measure (input). You would be hoping for some sort of nice straight line relationship.