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Old 1st October 2006, 03:59 PM   #1
jarthel is offline jarthel  Australia
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Default help with ntc thermistor

I decided to connect a 10ohm ntc thermistor on the "hot" wire of the IEC socket. I then connected the leads of the VOM on both leads of the thermistor.

from what I understand, an ntc thermistor's resistance will decrease. This is also the same in my situation. BUT once the resistance measures near zero, it begins to go up and down.

any ideas?

thank you.
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Old 1st October 2006, 04:05 PM   #2
lgreen is offline lgreen  United States
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Default ntc

Not sure what a VOM is (voltmeter?) but if the load is not drawing constant current, the thermister may cool off and resistance will rise.

Just to restate the obvious...if you are using a voltmeter, are you measuring voltage or resistance across the thermister? You want to measure the voltage across it, if the power is "on" not resistance.
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Old 1st October 2006, 04:08 PM   #3
jarthel is offline jarthel  Australia
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Default Re: ntc

Quote:
Originally posted by lgreen
Not sure what a VOM is (voltmeter?) but if the load is not drawing constant current, the thermister may cool off and resistance will rise.

Just to restate the obvious...if you are using a voltmeter, are you measuring voltage or resistance across the thermister? You want to measure the voltage across it, if the power is "on" not resistance.

volt-ohm-meter (old school here even though the meter I've used in university 10 years ago are digital)

the current load is constant since they are tube heaters. (B+ supply isn't connected yet. just testing the DC supply).

I thought measuring resistance would have the same effect as measuring voltage?
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Old 1st October 2006, 04:41 PM   #4
poobah is offline poobah  United States
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You can't measure resistance of a live circuit... you can even roast your meter.

You can measure the voltage though...
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Old 1st October 2006, 04:57 PM   #5
jarthel is offline jarthel  Australia
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Quote:
Originally posted by poobah
You can't measure resistance of a live circuit... you can even roast your meter.

You can measure the voltage though...

I never knew that.

I did measure the voltage and the thermistor seems to work as intended.

thanks for the help
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