Best way to get 4 temp measurements
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Posts: 46,084
I want to measure some temperatures under the hood. I have read a
lot about the OW stuff and even found an obscure reference on
multiplexing sensors. I want to pick everyones brain and find out
what you have done. Note that I didn't say "inside the engine" ie
combustions temps, I am mostly interest in intake and ambient air
temps in various locations.
Thanks a bit
KK
lot about the OW stuff and even found an obscure reference on
multiplexing sensors. I want to pick everyones brain and find out
what you have done. Note that I didn't say "inside the engine" ie
combustions temps, I am mostly interest in intake and ambient air
temps in various locations.
Thanks a bit
KK
Comments
kaptnknemo@y... writes:
> I want to measure some temperatures under the hood. I have read a
> lot about the OW stuff and even found an obscure reference on
> multiplexing sensors. I want to pick everyones brain and find out
> what you have done. Note that I didn't say "inside the engine" ie
> combustions temps, I am mostly interest in intake and ambient air
> temps in various locations.
>
What is the highest temperature you would anticipate?
Sid
[noparse][[/noparse]Non-text portions of this message have been removed]
A cheap and easy way to do it is with LM34 sensors and an ADC. This would
only use 2 I/O pins from the stamp, and will be quite accurate. Get an ADC
with a bunch of inputs, and you will have left over ADC for stuff you think
of later. I like the TLC2543.
You could go even cheaper and use thermistors and the POT command, but it
will be less accurate. With all of the noise under a hood, I don't know if I
would go with digital sensors. Mind you, I have never done it, so maybe they
work quite well.
Jonathan
www.madlabs.info
Original Message
From: "Matt Evans" <kaptnknemo@y...>
To: <basicstamps@yahoogroups.com>
Sent: Thursday, October 09, 2003 9:32 AM
Subject: [noparse][[/noparse]basicstamps] Best way to get 4 temp measurements
> I want to measure some temperatures under the hood. I have read a
> lot about the OW stuff and even found an obscure reference on
> multiplexing sensors. I want to pick everyones brain and find out
> what you have done. Note that I didn't say "inside the engine" ie
> combustions temps, I am mostly interest in intake and ambient air
> temps in various locations.
>
> Thanks a bit
>
> KK
>
>
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Body of the message will be ignored.
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>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
You could optimize my wine thermometer for ambient temperatures, I guess. It
needs only a BS2 and a couple of small and inexpensive sensors. For what I
have seen from digital thermometers (error +/- 1 or 2 degrees) this one will
be far more accurate.
Klaus
Hi,
I'm develloping a fast and accurate thermometer with the BS2 to meaure the
temperature of (good) wine. The sensor is a miniture NTC as used in fever
thermometers.
The resistance and the slope of the nearly exponential curve of the sensor
are specified in in 5-degree intervals by the manufacturer. I.e. 100 kOhm
and 4.7 kOhm/degree at 20 degree C.
I develloped an aproximation by 4 straight lines over 5-degree intervals.
The intervals are: below 12.5C, between 12.5C and 17.5C, between 17.5C and
22.5C and above 22.5C. For a thermometer for wine this makes sense to me.
The result is a very fast responding (2 seconds for a full reading) and
fairly accurate (error ca. 0.2C absolute) measuring instrument.
If I had done this using LOOKUP, as I planned first, I would have ended up
with a table of about 200 elements for this acuracy and resolution. The
NO-GO for this table was when I realised that if small corrections would
have to be made in a later stage of calibrating the system I would have to
work over the entire table, or mess up my code.
The code and the formulas I used are listed below.
Next thing to do is write the code for a display and fix the decimal point
:-).
Klaus
'///////////////////////////////////////////////////////////////////////////
///
' Ts = Cx - RT/Cy Ts: Temperature of sensor * 10
' RT: output of RCTIME
' Cx = T_cal + R_cal/(dR/dT)_cal cal: 10,15,20,25 degree C
' Cy = K*(dR/dT)_cal (dR/dT): slope of curve
' K = 29,57 K: system constant for BS2 and cap = 0.47 uF
'{$STAMP BS2}
OUTPUT 15
Ts VAR WORD
RT VAR WORD
Main:
OUT15 = 1
HIGH 12
PAUSE 10
RCTIME 12, 1, RT
OUT15 = 0
Ts = 479 - (RT/107)
IF Ts>225 THEN Label1
Ts = 420 - (RT/139)
IF Ts>175 THEN Label1
Ts = 367 - (RT/177)
IF Ts>125 THEN Label1
Ts = 306 - (RT/231)
Label1:
DEBUG CLS, DEC Ts, " RT= ", DEC RT
PAUSE 440
GOTO Main
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Oorspronkelijk bericht
Van: Matt Evans [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=y7Jvcihp_VylZEh1RoH3WDhvua8JjRtGlqPcEnRxJ6hVHlvq5pHwLVKWgEhstg-4XRbaVCYzj1g5AaD1]kaptnknemo@y...[/url
Verzonden: donderdag 9 oktober 2003 17:32
Aan: basicstamps@yahoogroups.com
Onderwerp: [noparse][[/noparse]basicstamps] Best way to get 4 temp measurements
I want to measure some temperatures under the hood. I have read a
lot about the OW stuff and even found an obscure reference on
multiplexing sensors. I want to pick everyones brain and find out
what you have done. Note that I didn't say "inside the engine" ie
combustions temps, I am mostly interest in intake and ambient air
temps in various locations.
Thanks a bit
KK
To UNSUBSCRIBE, just send mail to:
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its range is 32F to err, forget now.. Its output is 10mV/degree F. Does that
mean it puts out 0mV at 32F and you have to add 32 to the reading? The other
flavours of the LM34 go much lower, -35 or something. The datasheet is mum
about how to convert the mV reading to degrees. I would assume it means 32mV
at 32F and anything below that is unreliable (otherwise why not a rating
starting at zero?).
Any clues?
>
Original Message
> From: Jonathan Peakall [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=6YZh5AQwiXq4fwcBpo6xAf_Ch_BhwKIlmXd3lpZqlzU4_Nf9Y9tCV6jPzU--hjQMXkgnRt-dMkCLusR_sw]jpeakall@m...[/url
> Sent: October 9, 2003 9:52 AM
> To: basicstamps@yahoogroups.com
> Subject: Re: [noparse][[/noparse]basicstamps] Best way to get 4 temp measurements
>
>
> KK,
>
> A cheap and easy way to do it is with LM34 sensors and an ADC. This would
> only use 2 I/O pins from the stamp, and will be quite accurate. Get an ADC
> with a bunch of inputs, and you will have left over ADC for stuff
> you think
> of later. I like the TLC2543.
>
> You could go even cheaper and use thermistors and the POT command, but it
> will be less accurate. With all of the noise under a hood, I
> don't know if I
> would go with digital sensors. Mind you, I have never done it, so
> maybe they
> work quite well.
>
> Jonathan
>
> www.madlabs.info
>
looked it up. It does indeed just use direct readings i.e. .753 volts is
75.3F.
Hmm, wonder why they don't just rate it for 0-300...
>
Original Message
> From: PatM [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=vFz6YKEOyzo9vi_eh3xBem05LW22bFmIDpBRDypcyuCLzSDWrnyWssrF-BjLmxwhtY_tOC2QoAZq]pmeloy@s...[/url
> Sent: October 9, 2003 10:15 AM
> To: basicstamps@yahoogroups.com
> Subject: RE: [noparse][[/noparse]basicstamps] Best way to get 4 temp measurements
>
>
> I looking at the LM32DZ (the cheapest one). Something that perplexes me -
> its range is 32F to err, forget now.. Its output is 10mV/degree
> F. Does that
> mean it puts out 0mV at 32F and you have to add 32 to the
> reading? The other
> flavours of the LM34 go much lower, -35 or something. The datasheet is mum
> about how to convert the mV reading to degrees. I would assume it
> means 32mV
> at 32F and anything below that is unreliable (otherwise why not a rating
> starting at zero?).
>
> Any clues?
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the
> Subject and Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
converters that are fully compensated. Maxim will sample 2 at a time
for free.
I have used these and are fairly accurate at +- 2 C and can handle
temps up to 1000 C with the MAX6675.
You will need to use K type thermal couple wire which is available
from Digikey.
Jason
--- In basicstamps@yahoogroups.com, PatM <pmeloy@s...> wrote:
> Actually, I just recalled that the industrial control text uses an
LM34 so I
> looked it up. It does indeed just use direct readings i.e. .753
volts is
> 75.3F.
> Hmm, wonder why they don't just rate it for 0-300...
>
>
> >
Original Message
> > From: PatM [noparse][[/noparse]mailto[noparse]:p[/noparse]meloy@s...]
> > Sent: October 9, 2003 10:15 AM
> > To: basicstamps@yahoogroups.com
> > Subject: RE: [noparse][[/noparse]basicstamps] Best way to get 4 temp measurements
> >
> >
> > I looking at the LM32DZ (the cheapest one). Something that
perplexes me -
> > its range is 32F to err, forget now.. Its output is 10mV/degree
> > F. Does that
> > mean it puts out 0mV at 32F and you have to add 32 to the
> > reading? The other
> > flavours of the LM34 go much lower, -35 or something. The
datasheet is mum
> > about how to convert the mV reading to degrees. I would assume it
> > means 32mV
> > at 32F and anything below that is unreliable (otherwise why not a
rating
> > starting at zero?).
> >
> > Any clues?
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed. Text in the
> > Subject and Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
> >
> >
> >
this is very easy to do. Parallax has some code for I/C and C/A thermocouples.
A small kit should be available soon.
Chuck
The output of the LM34 at 32 degrees Fahrenheit is 320 millivolts.
All of the LM34 grades have the same equation. degF = millivolts/10
(+/- a fraction of a degree to 3 degrees for accuracy spec, depending
on the grade and the individual unit)
Look at the "specified operating temperature range" on the data
sheet for the different grades. The best grade, ($$) is speced from
-50 to +300 F, the middle grade from -40 to +240 F, while the
cheapest LM34DZ from +32 to +212. This has to do with the packaging
and with the testing they do on the chip. You can use the lower
grade beyond their rated temperature range, and they will follow the
same equation, but the accuracy is not guaranteed. And the plastic
package may fail at extremes.
To reach the negative temperatures, you need a resistor connected
from the output down to a negative power supply. Then the output at
-20 degrees F will be -200 millivolts. You need a system that can
read that. One nice thing about the LM34 is that it can read down to
nearly 0 degrees F on a single supply, well below freezing.
Another option is the AD590 temperature sensor. Or for high
temperatures, thermocouples with the MAX6674 or MAX6675.
Here is some more temperature sensor/stamp info:
<http://www.emesystems.com/BS2index.htm#interface>
-- best regards
Tracy Allen
electronically monitored ecosystems
http://www.emesystems.com
mailto:tracy@e...
>I looking at the LM32DZ (the cheapest one). Something that perplexes me -
>its range is 32F to err, forget now.. Its output is 10mV/degree F. Does that
>mean it puts out 0mV at 32F and you have to add 32 to the reading? The other
>flavours of the LM34 go much lower, -35 or something. The datasheet is mum
>about how to convert the mV reading to degrees. I would assume it means 32mV
>at 32F and anything below that is unreliable (otherwise why not a rating
>starting at zero?).
>
>Any clues?
>
>
>>
Original Message
>> From: Jonathan Peakall [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=q_sJwzEkckabb3dGzQfv1wGpDDmlRUofEQG92UOj-mZiMCyzlogXuehhIfoxfhliZ_1kPCr_xBhpixgY]jpeakall@m...[/url
>> Sent: October 9, 2003 9:52 AM
>> To: basicstamps@yahoogroups.com
>> Subject: Re: [noparse][[/noparse]basicstamps] Best way to get 4 temp measurements
>>
>>
>> KK,
>>
>> A cheap and easy way to do it is with LM34 sensors and an ADC. This would
>> only use 2 I/O pins from the stamp, and will be quite accurate. Get an ADC
>> with a bunch of inputs, and you will have left over ADC for stuff
>> you think
>> of later. I like the TLC2543.
>>
>> You could go even cheaper and use thermistors and the POT command, but it
>> will be less accurate. With all of the noise under a hood, I
>> don't know if I
>> would go with digital sensors. Mind you, I have never done it, so
> > maybe they
> > work quite well.
> >
> > Jonathan
> >
> > www.madlabs.info
> >
wrote:
> I want to measure some temperatures under the hood. I have read a
> lot about the OW stuff and even found an obscure reference on
> multiplexing sensors. I want to pick everyones brain and find out
> what you have done. Note that I didn't say "inside the engine" ie
> combustions temps, I am mostly interest in intake and ambient air
> temps in various locations.
>
> Thanks a bit
>
> KK
look at DS1822 I just posted