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'[OT]: Temperature Sensors?'
2002\11\30@233702 by Peter McNulty

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Hi,

What temperature sensors would you recommend for:

-Fast Response Time (90% of actual temp)
-Relatively Cheap (This is a school project, so nothing that costs $100)
-EASY to program for using PIC16F877 - This is a must! Themistors are looking to be very difficult to program for, for a nice accuracy
-Accuracy of sub +- 1degreeC

I've looked at the LM335 solution, but the response time is very long compared to other things, and so is the maxim chip. I've also messed around with thermistors, just printing out an ADC value and they seem to vary the most, but they are hard to program for as they are non-linear, and they change over age. RTD's look good, but i can't get a definate price on these things yet, and they are linear with a fast response time. Thermocouples I haven't really thought about, though i don't know if  they have thermocouples for the range of -50C to 100C with a nice accuracy, fast response time and easy programming. Are thermocouples linear?
Are there any other solutions i haven't thought of? What are your opinions of solution i need?

Thanks
-Peter

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'[OT]: Temperature Sensors?'
2002\12\01@003948 by Wagner Lipnharski
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Peter McNulty wrote:
{Quote hidden}

Peter, linearity can only be found by paying $, on Maxim or Dallas chips.

Any other sensor needs calibration and linearization, not always by the
sensors (case of the PT100), but mostly by your circuit out of precision.

If you think thermistors are difficult to deal with, just forget about
thermocouples. They give you millivolts (and microvolts) in a total non
linear range.

At this +-1°C accuracy you will need to go for calibration, no other way.

Calibration means you use any kind of sensor, but then needs to calibrate
individually each unit based on fixed temperature standards, ice point
(0°C), water boiling (100°C) and intermediate temperature points, then your
device software will interpolate the non calibrated mid points.  It means,
as much points you calibrate, better accuracy you get.  Except of course if
you want to start to play with polynomial math to do linearization without
table and interpolation.

It is NOT an easy task.

Very cheap sensor?  try to measure the Voltage Drop across a 1N4148 small
glass diode and change temperature...
A 10k NTC also is a nice unit, but none will give you 1°C accuracy for
free.

VV46NER

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2002\12\01@035024 by Dominic Stratten

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Peter - take 4 x 1N1418 diodes and connect them in series. Also connect a 1k
resistor in series with the whole lot and bung it onto a 5v supply. You will
get a suprising linearity and repeatability of results not to mention the
fact that you can measure a wide range of temperatures (I've tried over 300
degrees C and its still settled back to room temperature afterwards).

Worth a go for 10c worth of components

Dom
{Original Message removed}

2002\12\01@130835 by Victor Faria

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while we are talking about temp controllers!
does anyone know of a simple thermocouple circuit using a pic or????
I would need the temp to go up to about 200c
also are the adc features in the pics sensitive enough to
sense the low output of the thermo couple with out amplification?
regards
victor

{Original Message removed}

2002\12\01@133642 by Quentin

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> while we are talking about temp controllers!
> does anyone know of a simple thermocouple circuit using a pic or????
> I would need the temp to go up to about 200c
> also are the adc features in the pics sensitive enough to
> sense the low output of the thermo couple with out amplification?

No, the changes are small and non-linear.
Analogue Devices got a chip for thermocouples.
products.analog.com/products/info.asp?product=AD597
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2002\12\01@140140 by Dominic Stratten

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Try the 3 to 4 diode in series trick (with resistor). They are suprisingly
linear and I've managed to get 2 in series to hook up to a 10 bit a2d on the
pic with suprisingly good results. I did the original testing for
temperature swings on them using a mini blowtorch and they have survived
(although they are a bit sooty at the moment).

I almost dismissed the idea when I googled it and saw it mentioned but at
0.01 ukp per sensor (1N1418) it seemed worth a try. Just be careful about
extreme temperature swings - you will crack the glass case if you transfer
it straight from an ice bath to heated oil.

If a diode drops 2.2mv (approx) for every degrees C - use 4 or 5 of them in
series to give around a 10mV drop per degree. The other interesting thing I
noticed was the tolerance between diodes was within 1% for the batch I had -
made it much easier to mess about with other designs.

Dom

{Original Message removed}

2002\12\01@143748 by Dave Dilatush

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Victor wrote...

>while we are talking about temp controllers!
>does anyone know of a simple thermocouple circuit using a pic or????
>I would need the temp to go up to about 200c
>also are the adc features in the pics sensitive enough to
>sense the low output of the thermo couple with out amplification?

Without amplification, a thermocouple's output is nowhere near
large enough to be read directly by a PIC's A/D converter.

Look on Microchip's web site for Application Note AN684, "Single
Supply Temperature Sensing with Thermocouples".  This appnote
contains a lot of good information on using thermocouples, as
well as complete circuits for interfacing them to PICs.

DD

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2002\12\01@171253 by Ray Gallant

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Peter McNulty wrote:
{Quote hidden}

I would recommend a 100R or 1K platinum RTD.  About  $3.50 CDN.  You can get
free samples on your own.  Spend your money on your front end and Vref
accuracy.  Use a table derived from the available formulas for cold and
warmer temperatures.  If you go that route check out DIN- EN60751 class-x
and other standards.  The drift on some of these RTDs are minimum and if
your circuit is very stable, you won't need to calibrate, just a
verification is required.  You may need a DC offset due to the temperature
range.  I use RTDs from Heraeus with great results.  You can also design a
programmable home-grown temperature chamber (-30 to +30 deg C) for about
100 - $150 with a camper's cooler, darlington, relay & pic.
Regards,  {slewrate}

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2002\12\01@180208 by Spehro Pefhany

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At 06:08 PM 12/1/02 -0400, you wrote:


>   Spend your money on your front end and Vref
>accuracy.

Err.. why would you care in the slightest about Vref accuracy?

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2002\12\01@224559 by Wagner Lipnharski

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Ray Gallant wrote:
> I would recommend a 100R or 1K platinum RTD.  About  $3.50 CDN.  You
> can get free samples on your own.  Spend your money on your front end
> and Vref accuracy.  Use a table derived from the available formulas
> for cold and warmer temperatures.  If you go that route check out
> DIN- EN60751 class-x and other standards.  The drift on some of these
> RTDs are minimum and if your circuit is very stable, you won't need
> to calibrate, just a verification is required.  You may need a DC
> offset due to the temperature range.  I use RTDs from Heraeus with
> great results.  You can also design a programmable home-grown
> temperature chamber (-30 to +30 deg C) for about 100 - $150 with a
> camper's cooler, darlington, relay & pic. Regards,  {slewrate}

The only problem with RTDs and NTCs is its top temperature.

The RTD Panasonic ERTD2FHL103S (Digikey $1.06) goes from -30 up to +125°C
only!!!

The NTC Thermometrics Global AL03006-5818-97-G1 (Digikey $2.66) goes
from -50 to +204°C (+400°F) only.
If you need to cook SMD, it needs to go at least to 450°F, obviously should
operate at least up to 20% more, or, around 530°F.

A THERMOPILE is a nice non-contact sensor, that can measure the temperature
away of it.
The MLX90247B (Digikey $13) in TO39 4 leads, generates 40uV/K and it
incorporates a 26 kohms PTC in the same die, so you can compensate ambient
temperature.  Even that operating temperatures should be from -40 to
+150°C, this is the thermopile temperature, not the reading non contact
temperature, even that I could not find its reading temp range.
http://www.melexis.com website can give you more details about this chip.
They also have modules with complete solutions, digital or analog output,
but be aware of their $65 prices.

VV46NER

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2002\12\01@230506 by Spehro Pefhany

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At 10:41 PM 12/1/02 -0500, you wrote:

>The only problem with RTDs and NTCs is its top temperature.
>
>The RTD Panasonic ERTD2FHL103S (Digikey $1.06) goes from -30 up to +125°C
>only!!!

RTDs will go up to hundreds of degrees C. Whatever that part number is,
it is NOT an RTD, probably a thermistor.

>A THERMOPILE is a nice non-contact sensor, that can measure the temperature
>away of it.
>The MLX90247B (Digikey $13) in TO39 4 leads, generates 40uV/K and it
>incorporates a 26 kohms PTC in the same die, so you can compensate ambient
>temperature.  Even that operating temperatures should be from -40 to
>+150°C, this is the thermopile temperature, not the reading non contact
>temperature, even that I could not find its reading temp range.

That's interesting. Quite nonlinear output if it's the bolometer style.
They are much cheaper in high volume, but it's nice to see a source
for small quantities.

Thermocouples and RTDs are "almost" linear, in the case of RTDs,
linearity correction is easily done in hardware, of course in either
case you can use software. Because the nonlinearity is small (a few
percent) you don't need to worry about dynamic range of the front end.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
RemoveMEspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
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2002\12\02@002235 by Russell McMahon

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>A THERMOPILE is a nice non-contact sensor, that can measure the temperature
>away of it.
>The MLX90247B (Digikey $13) in TO39 4 leads, generates 40uV/K and it
>incorporates a 26 kohms PTC in the same die, so you can compensate ambient
>temperature.  Even that operating temperatures should be from -40 to
>+1500C, this is the thermopile temperature, not the reading non contact
>temperature, even that I could not find its reading temp range.

Introduction

       http://www.melexis.com/site/pr/tech_90247_release.htm

Intro data sheet / ordering info (pdf 11 pages)

       http://www.melexis.com/site/products/pdf/90247.pdf


$US2 / 100k quantity


       RM

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2002\12\02@073724 by Ray Gallant

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----- Original Message -----
From: "Wagner Lipnharski" <RemoveMEwagnerspamTakeThisOuTUSTR.NET>
To: <PICLISTEraseMEspam.....MITVMA.MIT.EDU>
Sent: Sunday, December 01, 2002 11:41 PM
Subject: Re: [OT]: Temperature Sensors?



The only problem with RTDs and NTCs is its top temperature.

The RTD Panasonic ERTD2FHL103S (Digikey $1.06) goes from -30 up to +1250C
only!!!

The NTC Thermometrics Global AL03006-5818-97-G1 (Digikey $2.66) goes
from -50 to +2040C (+4000F) only.
If you need to cook SMD, it needs to go at least to 4500F, obviously should
operate at least up to 20% more, or, around 5300F.

A THERMOPILE is a nice non-contact sensor, that can measure the temperature
away of it.
The MLX90247B (Digikey $13) in TO39 4 leads, generates 40uV/K and it
incorporates a 26 kohms PTC in the same die, so you can compensate ambient
temperature.  Even that operating temperatures should be from -40 to
+1500C, this is the thermopile temperature, not the reading non contact
temperature, even that I could not find its reading temp range.
http://www.melexis.com website can give you more details about this chip.
They also have modules with complete solutions, digital or analog output,
but be aware of their $65 prices.
--------------------------------------------------
VV46NER

The last RTD I used was -196 Deg C to 600 Dec C which is well within the
original post's range!
Regards, {slewrate}

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2002\12\02@074516 by Peter McNulty

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Do you know where to purchase RTD's online that ship internationally?
Digikey doesn't have RTD's and they don't give
very much information on what they are selling.

-Peter
{Original Message removed}

2002\12\02@080840 by Ray Gallant

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----- Original Message -----
From: "Peter McNulty" <RemoveMEpetermcnultyEraseMEspamEraseMEHOTMAIL.COM>
To: <RemoveMEPICLISTspam_OUTspamKILLspamMITVMA.MIT.EDU>
Sent: Monday, December 02, 2002 8:45 AM
Subject: Re: [OT]: Temperature Sensors?


> Do you know where to purchase RTD's online that ship internationally?

Google around & ask for samples.

http://www.electro-nite.be/

Regards, {slewrate}

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2002\12\02@100852 by Roman Black

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Hi, I checked a catalogue of replacement parts
for appliances, there are a few thermistors for
ovens, mainly microwave convection ovens (SHARP
smart ovens etc).

Sharp Thermistor; (similar TO-3 mount)
FH-HZA 011 WREO   (about $5 USD in singles)

This should be suitable for all typical oven
temps up to 220'C, but sorry I don't know what
resistance/temp curve etc. But unlike the diodes
this SHOULD be reliable for long term oven sensing.
:o)
-Roman

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2002\12\02@110202 by Chris Loiacono

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This is another reason that I love the PIClist.
I noticed that the Melexis website contains a mail link to a technical
contact person by the name of Dom Pompei. He holds numerous patents on
non-contact temp sensing, and was the founder of Exergen, Corp, also of NH,
USA, which he ran with his brother. I have known these guys for years and
have purchased 100's of their pre-packaged IR/TC (tm) non-contact 2-wire
sensors with standard tc output.

If the sensors described and being discussed here are based on the same
technology, which I believe  they are, the output is characteristically
beyond noisy. In fact, when first plotting it a few years ago, I assumed it
was pure garbage. Many PLC's have become completely confused when trying to
read them, even with moderate signal conditioning. (translation: PLC
unable - unfriendly at best) There is also a wide range of impedances these
parts are manufactured in, which is not controlled - I have parts in ranges
culled from their inventory to fill my orders.

My point is that it seems that Dom has found a new market channel for one of
his patent designs, which is a good thing, but to stress that it's probably
not very easy to use and will require significant programming expertise to
develop adequate filtering and a little more work than the usual in hardware
interfacing. For me it's a no-brainer to give it a go since it can save me
$50 or more per unit.

I don't know that this fits my own skill set so perfectly, but I do plan on
getting into it ASAP. I'll start with a message to Dom sarcastically
thanking him for letting me know that his technology was becoming available
at the component level.

I guess he likes selling me the $100 ea. packaged version...

Chris

{Quote hidden}

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2002\12\02@111625 by Dominic Stratten

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<Snip>
----- Original Message -----
From: "Chris Loiacono" <chrisSTOPspamspamspam_OUTMAIL2ASI.COM>
To: <spamBeGonePICLISTSTOPspamspamEraseMEMITVMA.MIT.EDU>
Sent: Monday, December 02, 2002 4:06 PM
Subject: Re: [OT]: Temperature Sensors?


> This is another reason that I love the PIClist.
> I noticed that the Melexis website contains a mail link to a technical
> contact person by the name of Dom Pompei.

<Snip>

Please note - its not me - I'm a different Dom ;-)


Regards

Dom

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2002\12\02@135744 by Mike Singer

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Peter McNulty wrote:
> Do you know where to purchase RTD's online that ship internationally?
> Digikey doesn't have RTD's and they don't give
> very much information on what they are selling.


> I only need a temp range of about -40 to 100 C


  Maybe Microchip's TCN75 2-Wire Serial Temperature Sensor and Thermal Monitor (21490b.pdf) will match.

Features:
Solid-State Temperature Sensing 0.5°C Accuracy (Typ.)
Operates from -55°C to +125°C

  Here in the Ukraine local Microchip folks sell them
for  $1.24 retail.

  Mike.

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