Author Topic: Thermometer to measure current  (Read 2077 times)

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Offline frank26080115Topic starter

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Thermometer to measure current
« on: November 16, 2007, 11:58:31 PM »
I have one of maxim-dallas' temperature measuring ICs, I noticed drawing a large current from it's binary output pin will cause it's temperature to rise significantly. Do you think I can measure current if i sanded the IC down and attached a thin nichrome wire to it so the IC measures the nichrome wire's temperature caused by current?

These ICs are sensitive to 0.5 degrees C, I'd probably use another sensor to get a room temperature reading to compare.

Offline HDL_CinC_Dragon

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Re: Thermometer to measure current
« Reply #1 on: November 17, 2007, 12:02:31 AM »
why not just stick a standard thermistor to it?
And also maybe put a big aluminum or copper heat sink on the IC?
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Offline frank26080115Topic starter

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Re: Thermometer to measure current
« Reply #2 on: November 17, 2007, 12:08:47 AM »
thermistors are horrible compared to these ICs, these outputs in degrees (digital, not analog voltage) with a eeprom to store thresholds so you can have it act as a digital switch if you needed it to

also, heatsink on the room temperature sensor is a good idea

Offline HDL_CinC_Dragon

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Re: Thermometer to measure current
« Reply #3 on: November 17, 2007, 12:14:35 AM »
So wait, is the problem that the IC is heating up thus giving false readings about the surrounding area? Perhaps im not understanding the problem/situation correctly?
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Offline nottoooily

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Re: Thermometer to measure current
« Reply #4 on: November 17, 2007, 12:59:55 AM »
You'll need to carefully control the thermal conduction between the resistor wire and the ambient for the temperature to mean anything. For example if it's in open air then a breeze will cause a lower temperature reading at the same current. If it's on a heatsink there'll be a long delay before it reaches steady state.

Perhaps you could put two sensors on a thermally insulated metal bar, with the heater at one end and any rough cooling at the other. From the two temperature readings and the known thermal conductivity of the bar you can calculate the power dissipated by the heater.

But why not just use an ADC to measure the voltage across the resistance wire?


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Re: Thermometer to measure current
« Reply #5 on: November 19, 2007, 05:56:32 AM »
To measure current, just use a current sense IC . . .

For temp measurements, my multimeter has a built in thermometer.

If I were to use an temperature measuring IC like you mentioned, I would actually use two. One would measure ambient/noise (not connected to anything), and one would measure ambient + something_else (connected to something).

Then just subtract the readings to just get something_else without the ambient noise (a breeze, light differences, etc).

 


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