EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Jebnor on July 16, 2013, 08:10:56 pm
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I'm selecting my resistors for my Mini Metrology lab. In the instructions, Mr. Hoffman suggests measuring Tempco by using a warm bath of Mineral Oil. While messy, it would be quite effective. Here's the rub, I don't have mineral oil hanging around. I do however have air-duster which I can use upside down to cool the resistors under test. Since I'm looking for two resistors with the same lowest possible TempCo, would this work? Do resistors have a different TempCo going hot vs. going cold? Do I risk breaking the resistors? The datasheet http://www.yageo.com/documents/recent/Leaded-R_MFR_2011.pdf (http://www.yageo.com/documents/recent/Leaded-R_MFR_2011.pdf) says the resistors have an operating range from -55C.
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You probably want a uniform steady state temp to take measurements, which you won't get with a can of freeze spray.
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You probably want a uniform steady state temp to take measurements, which you won't get with a can of freeze spray.
You will if you empty the whole can into a container and immerse the board under test into the liquid.
On a related note, Ive seen a LED that was designed for 2.8A take 12A+ while it was on a MCPCB and submerged in a bath of freeze-spray/duster. :o
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I'm selecting my resistors for my Mini Metrology lab. In the instructions, Mr. Hoffman suggests measuring Tempco by using a warm bath of Mineral Oil. While messy, it would be quite effective. Here's the rub, I don't have mineral oil hanging around. I do however have air-duster which I can use upside down to cool the resistors under test. Since I'm looking for two resistors with the same lowest possible TempCo, would this work? Do resistors have a different TempCo going hot vs. going cold? Do I risk breaking the resistors? The datasheet http://www.yageo.com/documents/recent/Leaded-R_MFR_2011.pdf (http://www.yageo.com/documents/recent/Leaded-R_MFR_2011.pdf) says the resistors have an operating range from -55C.
You can use any oil, if you verify it's completely isolatingl
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I'm selecting my resistors for my Mini Metrology lab. In the instructions, Mr. Hoffman suggests measuring Tempco by using a warm bath of Mineral Oil
Hi, I'm interested in what you are doing here and was wondering if you could point me to more information about this. I tried google without success
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Hi, I'm interested in what you are doing here and was wondering if you could point me to more information about this. I tried google without success
More info in another post I have. With links to the Articles. https://www.eevblog.com/forum/projects/mini-metrology-lab-build/ (https://www.eevblog.com/forum/projects/mini-metrology-lab-build/)
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Thanks!
With regards to spraying your resistors with coolant, I have recently been measuring resistor values versus temperature. Not having any means to control temperature I have been logging values over the coarse of a day's temperature variation and have found that as the temp increases so to does the resistance but there is a massive lag as temperature drops.
I then applied heat from a heat gun expecting to see resistance climb dramatically but saw it drop substantially, almost as though it went from PTC to NTC. I haven't investigated further but one idea I had is that extreme temperature gradients may be causing thermoelectric voltages throwing readings off :-//
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but did it return to its normal value afterwards? otherwise you may have just slightly melted the film or windings depending on the type,
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Yes it did return to nominal value. By heat gun I meant hot air reflow station, which I dialled down and measured around 150deg C on my thermistor prior to heating the resistor.
Good thought though and I'm open to any explanations
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I found some baby oil and placed some in a small glass dish in a hot water bath. The baby oil got to about 45C. In the end, I found two resistors that were dead-on ( as far as I can measure) matched to each other, and both had a zero change when going from room temperature (22C) to the oil at 44C. So I think I found a pretty good pair. :)
Now on to final packaging.