favorite temp sensors

No, I dealt with TC's in my youth, but I've been in recovery for decades.

Thinfilm RTDs are cheap. Here's one that I epoxied into a soda straw for outdoor temp measurement.

I used LM35's on far longer cables than this in years past. It's only a foot or less from the motor controller CPU to the JFET heatsink. There's not that much room under a Miata hood.

Good news, thanks. Now all we need is the same thing in a package that isn't such a good thermal insulator. ;)

Cheers

Phil Hobbs

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thermistor", 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

seem to be susceptible to integration onto silicon.

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We've all been thru that. I was "blessed" by the MIT ability to sleep in bursts, so I always drew bottle detail in the middle of the night. I could put the baby between us, prop up the bottle, and never roll over on the baby (X4 :-) ...Jim Thompson

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.

be susceptible to integration onto silicon.

ever much better. I'd have to redraw if before I could make any sense of it.

You're behaving like the brat. ...Jim Thompson

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", as I recommended earlier in this thread. I don't know when Yellow Spring s Instruments first introduced them, but I got told about their parts in 19

seem to be susceptible to integration onto silicon.

were > >ever much better. I'd have to redraw if before I could make any sen se of it.

Scarcely. Un-intelligible schematics are very nearly useless - too much ris k that a crucial detail will be misinterpreted.

Yes this is true. It is not clear that Jims way is simpler. As others have said, manufacturers have gone to a lot of trouble to get IC sensors that still do not achieve this. A 0.1% ratio reference resistor is cheap. If you don't want Bills bridge+adc, you can do something like this:

(opamp choice just for simulation)

Power dissipation is 0.7mW and thermal resistance to ambient air is 37C/W, which is 0.026C of self-heating, which isn't too shabby.

I like it.

There's an "exposed pad" under the device, which you could solder to a copp er ground pad, or couple - without electrical connection - with thermal con ductive adhesive. What kind of package did you have in mind - one of the op tions that National Semiconductor offered for the LM12?

They did have an order of magnitude less thermal resistance to ambient ...

which is 0.026C of self-heating, which isn't too shabby.

Ummm.. Bill, I _really_ question the general validity of that 37°C/W number in the datasheet .. I bet that's measured on a good-size chunk of FR4*.. think about putting a watt(!) into something that tiny. They don't state the coupon size in the datasheet. Fine, if you're measuring PCB temperature, maybe not fine otherwise.

A Pt100 at 0.2mA is 4uW, even a Pt1000 at the same current is still only 40uW- with similar surface area and a much nicer form factor.

Often the thermal impedance and response times of temperature sensors are 'optimistically' rated in air blasting at 3m/s or stirred oil.

BTW, note too that there is a temperature dependency in the power dissipation, especially in continous mode. At 1sps & 3V, power goes down to a fairly constant 150uW, which is more reasonable.

Can't complain too much though, it's the sort of thing that keeps food on the table and the wine fridge fairly well-stocked.

Best regards, Spehro Pefhany

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/W, which is 0.026C of self-heating, which isn't too shabby.

The exposed pad on the under-side of the package is for thermally coupling it to the board you mount it on. If you thermally couple that board to the object whose temperature you are measuring - in David Lesher's case, a copp er pipe - I can't see that there's going to be much of a problem.

The tiny packages haven't got much surface area, but they are thin,and ther e's not a lot of plastic packaging to slow down the heat flow. You may well be right, but it's not guaranteed.

It depends on the Pt100. If it's a thin film sensor on an alumina substrate , thermal resistance can be quite low. I got enthusiastic about that in pri nt back in 1978

Sloman, A.W. "On microdegree thermostats", Journal of Physics E: Scientific Instruments, 11, 967-968 (1978).

Probably not. Your TO-220 thermal resistance of 60°C/W is from junction t o air. The thermal resistance from junction to case is about 1.5°C/W, and it's a much fatter package than that of the ADT7320.

The ADT7320 quotes the junction-to-ambient at 37°C/W in still air, the j unction-to-case as 33°C/W. Thermistors are often quoted "in a stirred oil bath", but semiconductor manufacturers have a pretty well-defined set of r ules.

People not thinking about self-heating can also be good for an extra citati on ...

Sloman A. W. ?Comment on ?A versatile thermoelectric temperature contro ller with 10 mK reproducibility and 100 mK absolute accuracy? [Rev. Sci. Instrum. 80, 126107 (2009)] ?, Review of Scientific Instruments 82, 27101 - 027101-2 (2011).

There were claiming 100mK absolute accuracy while generating 200mK of self- heating in their thermistor. Clown car stuff.

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. >

to be susceptible to integration onto silicon.

that a crucial detail will be misinterpreted.

Maybe you need your reading glass prescription upped to a double lens stack? ...Jim Thompson

In my case it was. No calibration needed, and it handles an added-on external device to also measure temperatures away from the chip.

Some systems don't need +/- 0.2°C... particularly most of my stuff, which is commercial or even consumer level.

...Jim Thompson

A very old one I designed for Fairchild...

Explanation to follow... I'm off to the 5-year-old grandson's ice hockey practice... he made the team >:-} ...Jim Thompson

I recently designed a system to measure the temperature of the metal structure holding parts of a radar antenna up. The resolution was 0.1 C, and the accuracy was nominally 1.0 C, the purpose being to be able to calibrate over a range of temperatures with a reasonable number of temperature sensors. The cable between cabinet and measurement point was up to 10 meters long.

First tried thermocouples. The problem was getting the signal through standard mil-spec connectors - the junction from chromel-alumel to brass to copper was not temperature controlled, and things rapidly got complex.

Then tried thermistors. The beads were good enough, and the resistance was high enough to render cable resistance immaterial. But the ICs available to put on the circuit board had too few ADC bits, yielding too coarse a resolution.

Settled on platinum RTDs in a full Kelvin (4-wire) configuration, after finding a suitable IC from Maxim (or LT?). This chip is ratiometric, so we used a low-tempco metal-film resistor as the comparison. If people are interested, I'll look up the chip number.

Joe Gwinn

I used 1K platinum RTDs, 2-wire, and RG174 coax for my cabin automation temp sensing. The longest run is about 75 feet. I took out the coax resistance by calculation and got better than 1 deg C. I got compulsive (cabin fever?) and did an ice-point cal to final trim things up.

I did a simple mux thing with 0.1% resistors, ratiometric, all the math in PowerBasic.

There are some 24 bit SPI delta-sigma ADCs with two differential channels. Hang an RTD and a good resistor in series, across the ADC reference supply, and measure the two voltage drops, and do the math. That will measure RTD resistance to within a few PPM of the reference resistor. For the cabin, I wasn't *that* compulsive.

that a crucial detail will be misinterpreted.

He must be brain dead, if he can't read that. Maybe Farnell has a copy of the book: "Schematic Reading For The Rankest Of Amateurs" in stock for him.

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. >

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 was very impressed by your improvement (Figure 6) of the infamous four-wire-junction by a full 25%. ;)

Cheers

Phil Hobbs

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 think I've done eight, once.