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Old 27th September 2005, 06:39 AM   #1
lgreen is offline lgreen  United States
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Default Temp Probes- Question re operation of

I've got an Aerogate 3 fan controller running the fans in my amp and monitoring all heatsinks in the amp via 4 wired temp sensors which are black dual wires which meet at a sensor tip covered in kevlar or some similar tape. I've also got a DMM with a temperature probe-- a single metal tip that splits into to leads down the wire somewhere and plugs into a portable DMM in the normal + and - inputs to work only when temp is selected.

My question is how do these dealies work to sense temperature. I'm asking for 2 reasons-

1. I'd like to sense the temp of live heatsinks and both products say to probe isolated heat only. I can use insulators and thermal compound, but i'm already doing that and want a direct measurement.

2. I've fastened some of the Aerogate sensors underneath some plastic blocks (with thermal compound) but the mounting is pushing the sensors down to the heatsink with massive force. If the sensor requires a physical deflection due to heat I'm thinking my method of mounting might tend to give me lower readings due to the high pressure. If the leads just change in resistrance due to heat then i'm thinking that I am good to go- accuracy will not be affected since physical not electrial change is likely the onlyu drawback from pushing the probe onto the heatsink with such force.

anyway, i'm just wondering how these temp probes work so I can attempt accurate measurements, would appreciate input on the topic. thanks!
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Old 27th September 2005, 03:22 PM   #2
jcx is offline jcx  United States
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my guess is thermistor - a hi tempco semiconductor based resistor, if so the tiny bead may not like "massive force" as it is a brittle material

in principle force may modify a thermistor resistance but I'd worry first about breaking it, a compliant layer bewteen the sensor and the clamp would be good

Thermistor temp sensors are just ohm-meters with appropriate calibration for particular probe resistance curve -enough ac coupling from a live sink may interfere with their measurement circuitry - a battery powered meter is better because it can "float" at the heat sink potential (safety!)

using a compliant thermal separater/insulator (sil-pad or similar) helps the safety story if your "live" heatsink V is LIVE for safety purposes but no one is going to make a firm recomendation for fear of liability if you fry yourself
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