testing NTC caps

We special-ordered a reel (4000 pieces) of NTC caps from Capax. They are 0805, 3.3 pF, N4700. 23 cents each.

I figured I should test them. I made an oven out of a roll of solder, with the cap and a thermocouple inside.

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It has a nice long thermal time constant. I started with a heat gun to get it to 50C, covered it with a cloth, and took data slowly as it cooled. Near room temp, a spritz of freeze spray into the solder coil cooled it down, and then I took data as it slowly warmed up.

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The measured tempco is close to -7000, but that's OK. I'm going to compensate a 600 MHz coaxial ceramic resonator oscillator, with this cap and a series NPO padder, so too-high tempco is OK.

It would be great to have a very small benchtop oven, peltier hot/cold, to test small parts or circuits.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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John Larkin
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Den onsdag den 8. februar 2017 kl. 00.36.25 UTC+1 skrev John Larkin:

how small and what would you pay for one?

Reply to
Lasse Langwadt Christensen

There are small beer fridges that have heating capability too, for some reason, e.g.

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Personally I just use cold spray and a heat gun. ;)

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Reply to
Phil Hobbs

Warm beer? Yuk.

That might work, maybe connected to a DC power supply to adjust the temp. For $29, it's no big risk to try.

Me too. A little acetone squirted into my solder roll cools it nicely too.

We have a gigantic environmental oven, but it's a big deal to use. It would cool a keg to -70C.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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Reply to
John Larkin

Those very small fridges tend to use Peltier junction heat pumps, which are inherently bidirectional, but regular air-conditioners in Sydney tend to b e offered as bi-directional heat pumps, for cooling in summer and heating i n winter. I know of people in England who used heat-pumps for winter warmin g, but they needed to be quite big and expensive to deliver enough heat to warm a poorly insulated English house in an English winter.

Cheapskate.

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Bill Sloman, Sydney
Reply to
bill.sloman

Be sure to read the feedback. The plastic case has no insulation, the cold plate is on the bottom, and nothing to stir the volume.

Regards

Reply to
tom

For $2 more this gets to 300 F.

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Reply to
Tom Del Rosso

I use a vacuum flask with wadding in the neck. I use a small aquarium bubbler pump to pump air through silicone tubing via a power resistor (one with a cooling tube through the middle) through the wadding to the bottom of the flask. A cheap Chinese PID controller and solid state switch to heat the resistor closes the loop.

It's nice and even, low power and can be left on for days.

Cheers

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Clive
Reply to
Clive Arthur

I don't really need the case. Just a small hot/cold platform would work for testing parts or small circuits. 0 to maybe 80C would be enough. I'd have to deal with condensation, but there are ways to do that.

I could sit my solder-roll thing on the platform. Or a die-cast box with feedthrus.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
John Larkin

A bit tough to cool with that setup, though.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Reply to
Phil Hobbs

I'd like to go from 0 to maybe 80C. I guess the ideal oven would be a small box that I can put my circuit inside, that would ramp slowly from high to low temp. If I don't want to bother to automate the measurements, I could use a kitchen timer to alert me every, say, 10 or 20 minutes to walk over to my bench and take my data. These measurements are better if the temperature changes slowly, and that makes this sort of thing tedious.

Our big oven will sweep temp, and even can be remotely controlled, but it's a big deal to get wires in and out of the chamber, from DUT to instruments. It's great for big-deal automated measurements of whole products, with custom software.

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John Larkin         Highland Technology, Inc 

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John Larkin

Just connect the resistor the other way round.

Cooling is much harder because of condensation, at least for boards or components. With my setup, and using a stainless flask, I can run at

200'C without problems.

Cheers

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Clive
Reply to
Clive Arthur

I have a beautiful Extech 3-channel thermocouple data logger that writes to an SD card. If it had a couple of ordinary ADC inputs, that would be about perfect, but alas.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

Of course. Silly of me.

Depends on how long you need it to run. Starting it out cold (e.g. by putting the open flask in a deep freeze overnight, with some sort of thermal mass in the bottom) would probably work fine. I used to use a chest freezer for this sort of thing, back when I worked out of my house. Nowadays I'd probably just use a heating loop and run it inside the freezer compartment of the lab fridge, for those rare cases where the heat gun and cold spray (a spray duster held upside down) aren't good enough.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

We were testing chip caps at a former employer in roughly the same manner. The idea was to match the tempco curve so that the two caps in a Colpitts oscillator would be roughly the same. However, we did it starting from hot and then going toward cold, so that moisture would not condense on everything. For hot, we used a hot air gun. For cold, a bottle of CO2. The test box (plastic pipe) was fairly well insulated to speed up the testing. To keep the test box from affecting the measurements, the cap was supported by two screws with point contacts and coil spring tension. We found that caps from different vendors and different lots varied considerably.

I vaguely recall that they do make such things designed to fit on common LRC bridges and meters. However, I couldn't find anything affordable at the time, so we built our own.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

What happened to your Labjack?

Reply to
John S

Put the cap meter, digital thermometer, and maybe a clock where they can all be seen at the same time. Set your digital camera to take a photo of the displays every 10 minutes. I do this for long term battery discharge testing. No computah required.

See my comment elsewhere about condensation problems going from low temp to high temp.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

I have three of them, but that requires writing code, which John doesn't want to do, I don't think. (LJ may have some logging program that works under Windows, but I wiped my last Win7 box when they changed the EULA so that they own the contents of my hard disk.)

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

Not for something simple like this cap test. And neither the temp meter nor the cap meter is interfaced.

I don't mind taking a dozen or so data points and plotting them by hand. Gets me out of my chair.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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Reply to
John Larkin

What kind of heat load? That's going to be decisive on whether Peltiers are pracdical.

Really? The one I use has big silicone rubber stoppers in the side. We just stick BNCs, loose wires, serial cables USB cables, etc, through and stuff the bung in. Nice fan to keep everything isothermal.

It does suck 3-phase power and I didn't spec the really low temperature refrigerant.

--sp

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Best regards,  
Spehro Pefhany
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Spehro Pefhany

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