LM34 to A/D

Neat. I wonder what their profit margins are on that one. Then again it's probably a small market.

I'd be tempted to buy a reel of BFG hotrods and try out a discrete version. Of course only if the production volume is high enough.

We attempted a home-made distributed amplifier, using gaasfets, with mediocre results, and gave up when we found the Hittite gadgets. It's a distributed amp internally, and they have a lot less parasitics (and a lot more engineers) than we do.

But they sure get hot!

John

I don't, and will never, trust averaging an acquisition synchronized to a digital clock. Use the cheap code to correct for gain and offset of the cheap gain amp, which can be calibrated with a cheap voltage input.

You seem to be making the assumption that the noise would only be introduced _after_ the op-amp.

Just messin' with ya. :-)

These days, it's hard to make any other kind of acquisition. I almost always software lowpass filter stuff like this, slow things like temperature acquired by a fast sampling ADC. There's usually enough natural noise floating around to dither a 12-bit system up to 14 or even 16 bits of usable resolution. And if there's a high temp shutdown or something like that, filtering avoids false alarms from spikes or whatever.

He can calibrate based on a temperature standard, in the extreme. We don't know if he wants to store custom cal factors per system.

John

Since the temperature uncertainty of the '34 is adequate he does not need a temperature calibration. He can use E96 metal film resistors for his gain and bias setup of the gain amp and calibrate those errors with a simple voltage input. The E96 metal film should track in ratio at

pleeze...

Or just use a thermistor. They've been good to me, they are cheap, they don't latch up, don't need a black cat to cross the alley from left to right for negative temps, and heck, they don't even require a uC with an ADC on board.

Yan,

You need to adjust the gain ad offset of the base lm34 output to fit the ad input range. You can achieve digitization past the 10mV/deg that the lm34 device outputs!

If you would like some assitnace with the hardware for you and the organization please contact me directly. I have significant experience with the device and the process you describe!

Marc

it

good

Or just use an op-amp with better DC characteristics for about the same price, and 0.1% resistors. The latter are no longer very expensive.

Best regards, Spehro Pefhany

Well, I suppose you did have a valid point. Grumble.

Somebody *does* make an opamp with a charge pump inside, BB I think, but it's only for the front end, so they can go r-r on the input without all the usual crossover artifacts.

John

Several LSB's of onboard noise? That's perfect for dithering the ADC!

John

It's funny what people use simple things like the LM34 for.

We have an oven system (large) that required even heating through out. The selected range goes from 180..220 F, So we redid the duct work and placed array of duct panels with DC servos motors to position them. Off the side of each Panel is a LM34 which gets tied into a major wire way over to a control center. each LM34 and motor is connected to a board in a card rack. Each Card has calibration points etc..

The LM34 goes into a comparator for a +/- pulse that drives a mini pic chip which controls the motor position. We bought the motors that had limits switches already in the motor mounts. The rest, we designed. had the boards etched for us and we assembled them etc.. This system regulates the heat radiation on the oven so perfectly now that each zone only varies no more than +/- 1 degree F from each other.

We didn't experience any of the oscillating or latch up problems that many have spoke of here.

The first next-gen Intel/AMD/etc. processor off the production line has a cost measured in the few billion dollars.

If they manage to sell more than a couple, of course, the cost of the development and the new-tech fab can be spread out over more than one chip!

I brush up against a few particular sectors of the semiconductor- processing-equipment companies (many of them in Jim's neighborhood) that sell equip that goes into fabs, and am continually astonished at the money scales involved in the big picture. Usually we're dickering over a few K$ in billing, not a few billion in billing, though!

Tim.

well you figrued out exactly where to put the cazapatators, to make em stable :-)

Marco

well,. maybe it was the 75 feet of 3 wire #26 of Signal Cable for each LM34 that contributed to it? :)