and
resistance
That would work. If I recall, my chip can be configured to do that.
Now I will need to look the chip up. I don't recall the number of bits, but it may have been 24. It wasn't fast. I used 100 ohm RTDs and Kelvin configuration because we were making about 100 units, I wanted zero cable sensitivity, and I didn't want anything to be fussy.
Joe Gwinn
as I recommended earlier in this thread. I don't know when Yellow Springs Instruments first introduced them, but I got told about their parts in 1974, and other people jumped an that particular band-waggon early on. I've bought Betatherm parts from Farnell which are just as tightly specified. >
seem to be susceptible to integration onto silicon.
were > >ever much better. I'd have to redraw if before I could make any sense of it.
that a crucial detail will be misinterpreted.
I have no clue as to what you are talking about. What is it with which that you are taking issue? ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
did
Hang
resistance
I was pricing some 16 bit SPI DAC's and I thought 55 bucks for an 8 pin chip was a little steep. So I can imagine what a 24 bit ADC cost...
Jamie
I've got Zeiss varifocal lenses, and they work fine, and I can take them off for close work - the short-sighted eye focusses perfectly on stuff that's between four and ten inches away
The problem isn't seeing the symbols, but the way they are organised - or not organised in this particular case - on the schematic.
There's an art to making a schematic easily readable, and you hadn't mastered it back then. Your recent stuff is much better, if still a bit wee\sk on grouping stuff by function.
-- Bill Sloman, Sydney
You seem to have imagined wrong
Newark lists the LTC2402 at $11 one-off, and the LTC2412 at $9.52, though they've got a promotion going on so today's price is only $7.41.
TI has similar parts that are cheaper. The ADS1226 seems to be $7.65 (1 to 9) from Mouser.
-- Bill Sloman, Sydney
did
Hang
resistance
AD7191 is under $4 at 1K. Delta-sigmas are cheap.
Octal 16 bit DACs are cheap nowadays, too, well under $1 per channel.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
So, can we count on you incorporating hockey metaphors into your posts? Say "deke" and "stick-handle", for starters?
Best regards, Spehro Pefhany
-- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
trimmed
I know not any of ice hockey "lingo". But Killian has certainly taken to it. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Hey Jon, I was thinking about this, and it seems like the error is due to the non-ideality factor (NIF) in the equation. Now I've only read about the NIF in the context of pn junctions, but wouldn't there be something similar in a diode connected transistor? Now according to Streetman the NIF arises because of carrier recombination in the transition region. I know when I looked at the temperature dependence of some pn diodes (maybe 1n4148's?) that the NIF was much closer to 2. So then what transitors would have NIF's close to 1? I wonder if they list NIF's in the spice models?
George H.
to pay
e into
bit
r CHi Joe that's neat, I'm a bit confused as to why platinum RTD's were easier thant thermistors? I've never used a platinum RTD.
George H.
one
trimmed
e y ...Jim Thompson ...Jim Thompson ...Jim Thompson"Keep your stick on the ice!"
George H.
"The Journey is the reward"
eff.com- Hide quoted text -
trimmed
[snip]Yep. A fundamental rule. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
1 h
ce
They aren't. I think that what Joe Gwinn was saying that he didn't discover 24-bit sigma delta A/D converters (mostly they aren't better than 20-bit, but they all produce three eight-bit bytes of output data)until after he'd decided to try the Platinum RTDs.
Pt RTDs give about +0.4% resistance change per degree Kelvin, thermistors a bout -4%, so they aren't easier to use. Their self-heating isn't usually as bad, and they don't go nuts if you put too much current through them, but it takes even a sophisticated user a while to get conscious of this kind of problem.
-- Bill Sloman, Sydney
The BJT models are rife with "emission coefficients," which is what I think you are talking about. In BJTs, my meager practical experience (small signal BJTs at low frequency and DC) is they really are very close to 1. Yes, an emission coefficient, if different than 1, would affect things. But only the step size. At least, given the simple models I was discussing earlier.
Diodes quite commonly have emission coefficients > 1. Some as high as 4 or more, I think. LTspice (I just checked) shows their single (I'm sure there should be more than one model as it is a widely sourced part) model having an emission coefficient of 1.752. Which is, as you say, much closer to 2 than to 1.
Yeah, they do. Forward, reverse, high current, low current, upside down, ... Go into LTspice, then access the Help. Search on Q. The just look down the list for emission coefficients. 5 of them pop up right away. If there is a modeled diode anywhere, backwards or forwards, there is a separate emission coefficient for it, I think. ;) Almost gives Rube Goldberg a run for his money.
If you see step size variations from part to part, but consistent within a given part, I'd tend to lump that one onto the simple emission coefficient. It's a quick fix. But step size variations over T on the same part? There is something else involved... or the single emission coefficient isn't enough... which is about the same problem.
It all comes down to teasing out what you can assign to a priori physics and remove from the modeling by applying a better physical model and what you are stuck gluing onto an existing model, which uses some mathematical behavior as a tool but where there is no real physics underneath it. It can get pretty hairy.
Assuming there is any additional fruit to be had using these as temperature sensors, better than the simple models provide, I think means delving into the deeper nature of the parts and not getting hung up tinkering on the high level modeling side. It's like the scenario where you are using a simple, small-angle pendulum model to understand the behavior of pendulums made by children. You can argue all day about tinkering with pasted on parameters to make the model match experience, but unless you delve deeper into how the kids are building them and see they are using different sized holes (and different diameter rods rocking in them) and develop a better more physically based model, those parameters will never get you that far. You'll be mired in limited degrees of freedom pasted to the wrong math models for the physics involved and never extracate yourself (with any remaining sanity.)
It would be fun to horse around trying to make really good T sensors from BJTs, if no one else had already scraped that bowl clean. But I suspect there have been a number of Ph.D.s already squandered without achieving a great deal more utility than we already see.
Did you do a single-point calibratation on your probe, by the way? Or how did you establish where on the absolute scale things were at?
Jon
I forgot to mention a big practical problem with thermistors - they are not much used in industrial temperature sensing where the "point" (the location being measured) is outside of the equipment shelter, so one cannot buy suitable *robust* industrial cables and probes. By contrast, thermocouples and RTDs are widely used for such things, and so are widely supported by multiple vendors.
The other problem was the unavailability of suitable ICs to convert thermocouple electrical signals into computer-readable data.
Joe Gwinn
That's why BJT's make better "diodes" than diodes do. M (or N, depending on whose equation) rarely varies from "1" in conventional BJT's... as long as you stay away from HV devices.
Beware: You _will_ occasionally see Spice models with M =/= 1. This is because the modelers don't know how to fit equations to data. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
pay
into
RTDs are very accurate and stable and are usable over a wide temp range, things that termistors aren't. Thinfilm platinum RTDs are fairly cheap, too, much cheaper than a thermistor of similar accuracy.
RTDs are easy to linearize, too, in hardware or software. I have somewhere around here a dual-opamp circuit that does 3-wire RTD conditioning with linearization. In software, a bit of second-order correction is usually all you need... just a few lines even in assembly.
Thermistors can be good over a narrow temp range where you want a lot of signal, like a crystal oven or some such.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
for close work - the short-sighted eye focusses perfectly on stuff that's between four and ten inches away
organised in this particular case - on the schematic.
it back then. Your recent stuff is much better, if still a bit wee\sk on grouping stuff by function.
You, Slowman, are just a wee bit "weak" (*) at following schematics. My drawings are hierarchical by function, AND by matching requirements. So it is a rarity that a component in one hierarchical block has to match something in another hierarchical.
(*) Maybe because you aren't capable of recognizing functions at the device-level ?>:-}
And your oscillator claims are down-right farcical. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
did
Hang
resistance
We're paying around a buck for eight channel, 24-bit, differential DACs and about a buck-fifty for four channel ADCs with input diagnostics. Delta-sigma audio stuff is really cheap.
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