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calibration "curves".

Hello

What is a calibration "curve"

My syllabus says that we need to

"-use calibration curves."


I have two problems with it:

1- I can not find anything relevent in my books.

2- I always thought that calibration graphs are STRAIGHT LINES, because measuring instruments are usually linear etc. So the term "CURVES" is confusing to me.:confused: :s-smilie: :frown:


By the way there is some more information in the notes, something about some experiment:

Expt: temperature measurement using a bead
thermistor


apparatus:
bead thermistor, ohm-meter, 10C - 40C water
bath, mercury-in-glass thermometer


:confused: :confused: :confused:
I dont know the exact definition of calibration but i know whats going on. You have two change the temp in the waterbath, measuring it with thermometer and then( i take it the bead thermistor is in the water bath and part of a circuit) measure the p.d. across the thermistor at given temps. eg, at 10 degrees the p.d is blah, at 20, it is blah, etc.you have to plot a graph. you should get a curve. then you can use this curve to measure temp without the thermometer. I think calibration is the part where you get the curve, coz you're, i dunno, calibrating the temperature or something.
Hashmi
Hello

What is a calibration "curve"

My syllabus says that we need to

"-use calibration curves."


I have two problems with it:

1- I can not find anything relevent in my books.

2- I always thought that calibration graphs are STRAIGHT LINES, because measuring instruments are usually linear etc. So the term "CURVES" is confusing to me.:confused: :s-smilie: :frown:


By the way there is some more information in the notes, something about some experiment:

Expt: temperature measurement using a bead
thermistor


apparatus:
bead thermistor, ohm-meter, 10C - 40C water
bath, mercury-in-glass thermometer


:confused: :confused: :confused:

Well firstly, a calibration is a conversion to a different set of units or to a more correct set of measurements from that which you are measuring. I'll give you 2 examples.

1. Say I have a ruler, and I measure from the end point of the ruler a distance along it to give the length of an object. However, my answer is consistently out by the distance from the end of the ruler to the "0" line on the ruler. I therefore need to apply a calibration and subtract this distance from all my results to give the actual result.

2. I put a wire in water, put a voltage across it and the temperature rises. The temperature is related to the voltage across it, so that if I know the voltage and the relationship between voltage and temperature I can convert from a unit that doesn't interest me (voltage) to one that does (temperature). The calibration curve is then a set of experimental results which relate the voltage to the temperature and give me the temperature for any voltage, so that I may convert between the two.

What you say about linearity is true normally for the unit it measures in. For example, if I double the voltage I expect it to read twice as much. However, this does not necessarily mean that if I double the voltage I double the temperature, because it depends on the relationship between the two. Therefore in general it will be a curve.

Make sense?

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