Once in an article... replacement of trimmers

We use "witness paint" on the Jesus nuts in aviation. You can get it in a multitude of colors and it does the same job ... if the nut loosens, the paint cracks and the inspection becomes rather trivial.

THanks,

Jim

For sealed trimpots, I like to use automotive touch-up paint. It comes in a good range of colors and with a little applicator brush in the cap.

Best regards, Spehro Pefhany

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I've got 'burger-flippers'* using DMM's to set some pot. If it's critical they have to come and use 'my' meter. Lot's of times a 5% measurement is good enough to see if something is working. Phil, do you have a favorite pot? I've been using the squarish ones from Bourns.

George H.

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That's OK though... how else do you learn, but by mis-adjusting something? George H.

Oh, no more than one trim pot per board. If there's two it takes a 'technician' to adjust it.

George H.

One of my first jobs was cooking fish and chips in a little stand on the Vancouver waterfront(*), so I'm not down on burger-flippers as a species--I'd just like folks to have enough opportunity to figure out what they're actually doing, which of course is what most people would want to do anyway.

I like the Bourns 3312J series--they're practically microscopic 1-turn cermet trimmers with pretty good vibration ratings. Joerg's right, though, one shouldn't use them in a product unless it's really necessary.

Cheers

Phil Hobbs

(*) I was about a foot taller than the other folks who worked there, so I was the only one who could see into the exhaust plenum when the filters over the deep fryers were removed for cleaning. The first time I saw it, I just about lost my lunch. I spent about half an hour bailing out an ocean of repulsive, stringy, rancid grease and cleaning the plenum with Lysol, a wire brush, and lots of paper towels. I still shudder when I think of it.

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Yeah! I don't want anyone flying my trim pot stuff. That's different, I want people to be able to change things if they want too.

George H.

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I've got a strong preference for the 3/4 inch (aka 19mm) 20-odd turn trimmers. They are big, but a nice long resistive element means that that they are finely settable - even the wire-wound versions - and there's not a lot of back-lash in the setting mechanism, and the slider tends to stay where you've put it.

For a while Vishay did a luxury version with multiple brushes on the wiper which was handy when you needed extremely fine settability, which we used on the Cambridge Instruments electron beam micro- fabricators when setting up what was essentially a 18-bit D/A converter.

It knocked about half an hour of the calibration time - about $15 worth of technician time at that time and place - which more than covered the extra dollar or two that the Vishay trimmer cost.

-- Bill Sloman, Nijmegen

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Granted, but sometimes the goal is not teaching, but fielding reliable equipment.[*]

I swapped out a load of trimpots for software and autocal in a piece of gear way back, but still needed a CMRR pot. Overall, t'was a good compromise.

-- Cheers, James Arthur

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I can only think of two that I've used in ~8 instruments. One determines the amplitude of a light bulb stabilized Wien Bridge oscillator. (They stopped making those 1% light bulbs... :^) and the other sets a current limit in a diode laser drive.

George H.

I took a year off from school as an undergrad. I was a cook in a fairly nice restaurant. I did get to flip a few burgers, but more steaks. Great motivation for going back to school!

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But then it's dead and the customer will steadfastly say the he not dunnit. The old sales mantra is that the customer is always right.

But yes, the shot noise is inevitable and can become a problem in your applications. Maybe you can nail an old laser trim machine on some auction site? They are also very useful for a lot of the more mechanical jobs.

Sometimes you can "burn" lightbulbs into the correct impedance at xxxx Kelvin if that's what you were after. I did that after the predecessor at my first job showed me a neat trick of using light bulbs as noise sources. So I used them for other stuff as well later because back then you could buy boxes of surplus watch bulbs for cheap. They were rated

I've worked at a meat factory as a kid. Didn't eat much meat for about a year after that. Very tough work but I think every person heading for an academic track should do a "manual labor" type job at least for a few weeks. Gives you a whole new appreciation for the people doings such jobs all year round. Just like splitting your own firewood, since having done it I never complained about the high prices of firewood again. Those people deserve the money.

I still shudder when thinking about that meat factory ...

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Grin... Don't ask what we pay for light bulbs these days.

Light bulbs as noise sources, Hey, I thought of that but never tried it. You crank up a light bulb to ~2000 K? Well whatever temperature you want. You could measure the noise, the bulb resistance and determine the temperature Then relate that to the bulb color... I bet someone's already done it.

At the moment I'm still young enough (53) to enjoy the physical labor of gathering wood. (after sitting on my butt all week.) There's also a lot of satisfaction in seeing a nice stack of wood grow. And security, let those winter storms blow! It's time to get the snow plow on the truck. We had a dusting of snow today.

George H.

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Actually it's even easier. You can calculate the temperature from the operating voltage/current (gives you the hot resistance which RF guys typically want to be 50ohms) versus the cold resistance.

I am not looking forward to winter. Tonight we'll have to fire up the wood stove, my wife doesn't like it when it drops to 65F in the living room. Every winter gets longer. Last year was a record, over five cords of almond. Meaning we had to "borrow" from the five cords we had bought for this winter. But with some luck I can pick up almost half a cord of pine next week but must split that. Some of it is seasoned so we can use that.

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OK, I can get the power and resistance from I and V. But I need a thermal resistance to calculate the temperature.

Oh, I really love winter. You've got to live where there is lots of snow and ice. And then wear the right clothes... It's no fun being cold.

Are you burning your wood inside? Pine out east here has a lot of stuff in it, which clogs up chimneys.

George H.

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Why? All you need is the hot/cold resistance ratio and knowledge about what filament is in there (tungsten, usually in the datasheet).

Or middle of this page:

Some folks even did SPICE sims on tungsten filaments. I wonder when the first guys will show up with the simulation of a Pale Ale brewing process :-)

No ten horses would drag my wife to such a place. Our ideal location would be where the word "winter" does not exist in people's vocabulary.

Same here, sap. The trick is to burn it correctly. Sap has a lot of energy in it. We have a modern stove with several combustion regions and you can make the sap fumes ignite and burn with a bright blue-white "cloud flame". The fans have to be cranked up because the stove will become friggin' hot.

But I don't like splitting pine because you get sap splotches and smears everywhere. On the driveway, under the shoes, in the clothes, on the skin ... yuck. I've also had it happen that the splitting maul made a squishy sound and was almost glued in place by sap.