Temperature co efficient of resistance help

AI Thread Summary
The temperature coefficient of resistance is not a constant for materials and varies with temperature, which is why it is typically referenced at a specific temperature, often 20°C. To determine the temperature coefficient at a particular temperature, resistance should be measured as a function of temperature, and the slope of the resulting graph can provide the coefficient. Thermistors exhibit significant non-linearity, with resistance potentially halving with every 8-degree increase in temperature, while metals generally display more linear behavior. For materials with a linear response, the coefficient at 20°C can be used to predict resistance at other temperatures. Reference charts and resources like the CRC Handbook or Wikipedia can provide additional data on resistivity and temperature dependence.
kocchumon
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is temperature co efficient of resistance a constant for a material?

if no how can i find the temperature co efficient of resistance at particular temperature?
 
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Measure the resistance as a function of the temperature, over the temperature range you want.

You can get the tempco from the slope of the graph.
 
kocchumon said:
is temperature co efficient of resistance a constant for a material?

if no how can i find the temperature co efficient of resistance at particular temperature?

No, it isn't constant. That is why the temperature coefficient is always quoted at 20 deg C or some specific temperature.
Thermistors are particularly non linear. Their resistance can drop to half with every 8 degrees increase in temperature.
Metals are much better than this.

I have seen charts of this non linearity for some specific metals. I think it might have been in the CRC Handbook of Chemistry and Physics. I don't have this book, but good libraries would probably have it.
Or, there is always Google.
 
vk6kro said:
No, it isn't constant. That is why the temperature coefficient is always quoted at 20 deg C or some specific temperature.
Thermistors are particularly non linear. Their resistance can drop to half with every 8 degrees increase in temperature.
Metals are much better than this.

I have seen charts of this non linearity for some specific metals. I think it might have been in the CRC Handbook of Chemistry and Physics. I don't have this book, but good libraries would probably have it.
Or, there is always Google.



if i don't hav a graph with t vs r then how can i fing the temperature so efficient?
 
You look it up on a chart. Other people have already done the measurements.

Some substances will give a straight line graph, meaning the coefficient is fairly constant with temperature.
Others will give a curved graph of R vs Temperature which means the coefficient is not constant with temperature.

With most metals the coefficient is linear enough that you can predict the resistance at other temperatures using the coefficient at 20 deg C.

Wikipedia has some data on resistivity and some formulae that describe resistor behaviour.
http://en.wikipedia.org/wiki/Resistivity#Table_of_resistivities
look for the section on temperature dependence.
 

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