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'[PIC] Measuring flow using a temperature sensor (a'
2010\02\06@150342 by Dario Greggio

face picon face
We've been considering measuring air flow (at some 1-2 bar) by using a
temperature sensor (possibly a I2C one such as MCP9800) and maybe a
heater coupled to it.

Do you think it's doable with some good precision? Of course the other
method would be using a fan or alike and an encoder but it's quite more
complicated... :)

thanks for any tip!

--

Ciao, Dario
--
Cyberdyne

2010\02\06@152934 by Richard Pytelewski

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face
Dario:

This EDN article may give you some ideas using transistors ... idea is
reasonable and could be updated to minimize popcorn parts.

http://www.edn.com/contents/images/91902di.pdf

Rich

{Original Message removed}

2010\02\06@155052 by Dario Greggio

face picon face
Richard Pytelewski ha scritto:
> This EDN article may give you some ideas using transistors ... idea is
> reasonable and could be updated to minimize popcorn parts.
>
> http://www.edn.com/contents/images/91902di.pdf
>

Thank you very much Rick! almost perfect!
Well, so the point is "keeping the difference between 2 sensors @50°C",
so this will cancel out the changes in incoming air temperature... I
suppose?
In fact, it was my point. Our needs are to measure some 0..40°C air flow.

--

Ciao, Dario
--
Cyberdyne

2010\02\06@155116 by Marc Nicholas

picon face
I built a sensor to monitor air conditioning in this way...I would think you
could apply the same principles.

-marc

On Sat, Feb 6, 2010 at 3:03 PM, Dario Greggio <spam_OUTadpm.toTakeThisOuTspaminwind.it> wrote:

{Quote hidden}

> -

2010\02\06@162342 by Richard Pytelewski

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face
That was the way I understood it... the transistor in the static air heated
to a "baseline" level and the transistor in the air flow temperature
fluctuated with the amount of air passing it.

Rich

{Original Message removed}

2010\02\06@170814 by Dario Greggio

face picon face
Richard Pytelewski ha scritto:
> That was the way I understood it... the transistor in the static air heated
> to a "baseline" level and the transistor in the air flow temperature
> fluctuated with the amount of air passing it.
>

Ok.
I'd use 2 MCP9800 and have some good precision and range.

--

Ciao, Dario
--
Cyberdyne

2010\02\07@094634 by Mohit (Lists)

picon face
This is done in "Thermal Mass Flow Controllers". It think
they are quite accurate and are used in applications that
cannot have the fluid flow disrupted by the measuring device
(f.e., rotameters).

Hope this helps,
Mohit.
http://www.BioZen.co.in.

Dario Greggio wrote:
> We've been considering measuring air flow (at some 1-2 bar) by using a
> temperature sensor (possibly a I2C one such as MCP9800) and maybe a
> heater coupled to it.
>
> Do you think it's doable with some good precision? Of course the other
> method would be using a fan or alike and an encoder but it's quite more
> complicated... :)
>
> thanks for any tip!
>

2010\02\07@111211 by Dario Greggio

face picon face
Mohit (Lists) ha scritto:
> This is done in "Thermal Mass Flow Controllers". It think
> they are quite accurate and are used in applications that
> cannot have the fluid flow disrupted by the measuring device
> (f.e., rotameters).


Yeah, I see, thank you. We don't have that need in this app, but the
point would be eaiser making-up and lower costs.

--

Ciao, Dario
--
Cyberdyne

2010\02\08@050350 by Michael Rigby-Jones

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> -----Original Message-----
> From: .....piclist-bouncesKILLspamspam@spam@mit.edu [piclist-bouncesspamKILLspammit.edu] On
Behalf
{Quote hidden}

more
> complicated... :)
>
> thanks for any tip!
>

What kind of range of airflows do you need to measure?  Perhaps an
automotive air mass sensor would be usable?

Regards

Mike

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2010\02\08@052105 by Mohit (Lists)

picon face
> Yeah, I see, thank you. We don't have that need in this
> app, but the point would be eaiser making-up and
> lower costs.
Actually mass flow controllers are costlier in the market.
But I can see that for an electronics guy, they are more
attractive. :-)

Mohit,
http://www.BioZen.co.in

Dario Greggio wrote:
> Mohit (Lists) ha scritto:
>> This is done in "Thermal Mass Flow Controllers". It think
>> they are quite accurate and are used in applications that
>> cannot have the fluid flow disrupted by the measuring device
>> (f.e., rotameters).
>
>
> Yeah, I see, thank you. We don't have that need in this app, but the
> point would be eaiser making-up and lower costs.
>

2010\02\08@055128 by Dario Greggio

face picon face
Michael Rigby-Jones ha scritto:

>
> What kind of range of airflows do you need to measure?  Perhaps an
> automotive air mass sensor would be usable?


some 200-400 lt/hour at circa 1-2 bar

--

Ciao, Dario
--
Cyberdyne

2010\02\08@120814 by Marco Genovesi

picon face
Dario,
this isn't exactly that you want, but may be useful due to the similar
problematics..

http://www.fonema.se/anemom/anemom.html


ciao,
Marco






{Original Message removed}

2010\02\08@122959 by Dario Greggio

face picon face
Marco Genovesi ha scritto:
> Dario,
> this isn't exactly that you want, but may be useful due to the similar
> problematics..
>
> http://www.fonema.se/anemom/anemom.html
>

Very nice link, Marco, thank you very much :)
Will take a look, more or less the path is chosen, 2 sensors, one in
free air and one coupled to a heater. We'd like to assemble them into a
30x30x100 aluminum case such as those that can be easily found, together
with air pipes.

--

Ciao, Dario
--
Cyberdyne

2010\02\08@130029 by Alex Harford

face picon face
On Mon, Feb 8, 2010 at 2:00 AM, Michael Rigby-Jones
<.....Michael.Rigby-JonesKILLspamspam.....oclaro.com> wrote:
>
> What kind of range of airflows do you need to measure?  Perhaps an
> automotive air mass sensor would be usable?

That's exactly what I was thinking.  What kind of airflow do you need?
Is it comparable to a VW engine?

www.idparts.com/catalog/product_info.php?products_id=242

2010\02\08@130913 by Dario Greggio

face picon face
Alex Harford ha scritto:
> On Mon, Feb 8, 2010 at 2:00 AM, Michael Rigby-Jones
> <EraseMEMichael.Rigby-Jonesspam_OUTspamTakeThisOuToclaro.com> wrote:
>> What kind of range of airflows do you need to measure?  Perhaps an
>> automotive air mass sensor would be usable?
>
> That's exactly what I was thinking.  What kind of airflow do you need?



Early this morning I've received an Offer by Sensortecnichs -
some 90EUR for a 0-5V sensor, capable of 1-2bar and 360 lt/hour.

--

Ciao, Dario
--
Cyberdyne

2010\02\08@131139 by Dario Greggio

face picon face
Alex Harford ha scritto:

> That's exactly what I was thinking.  What kind of airflow do you need?
>  Is it comparable to a VW engine?
>
> http://www.idparts.com/catalog/product_info.php?products_id=242



hmmm, I can't find any spec about it...

I need more or less what I've been offered as per my previous mail.

thanks Alex!

2010\02\08@134108 by Bob Blick

face
flavicon
face

On Mon, 08 Feb 2010 19:09:03 +0100, "Dario Greggio" said:
> Alex Harford ha scritto:
> > On Mon, Feb 8, 2010 at 2:00 AM, Michael Rigby-Jones
> > <Michael.Rigby-Jonesspamspam_OUToclaro.com> wrote:
> >> What kind of range of airflows do you need to measure?  Perhaps an
> >> automotive air mass sensor would be usable?
> >
> > That's exactly what I was thinking.  What kind of airflow do you need?
>
>
>
> Early this morning I've received an Offer by Sensortecnichs -
> some 90EUR for a 0-5V sensor, capable of 1-2bar and 360 lt/hour.

That's probably a good choice. It's hard to make an airflow sensor
measuring low flow rates. Automotive MAF sensors are for hundreds of
times as much air.

Back to the one that used two transistors heated to 50C. I built that
many years ago when it forst appeared, because it was charming. Although
it does work, plain transistors are awful. There is too much thermal
mass. It takes a minute to stabilize and response to changing flow rates
was wobbly.

Cheerful regards,

Bob

--
http://www.fastmail.fm - The professional email service

2010\02\08@134519 by Alex Harford

face picon face
On Mon, Feb 8, 2010 at 10:11 AM, Dario Greggio <@spam@adpm.toKILLspamspaminwind.it> wrote:
> Alex Harford ha scritto:
>
>> That's exactly what I was thinking.  What kind of airflow do you need?
>>  Is it comparable to a VW engine?
>>
>> http://www.idparts.com/catalog/product_info.php?products_id=242
>
>
>
> hmmm, I can't find any spec about it...

IIRC they output a square wave but I don't recall the frequency, and
don't know the conversion.  My Firebird used this system but that was
2 cars ago so it's mostly forgotten now.

> I need more or less what I've been offered as per my previous mail.

I think that is a good deal, I remember the prices on MAF sensors were
quite high for my car, in the $300 CAD range.  But that is probably
due to automotive ranges, and it had a burn-off circuit that heated
the wire extremely hot to clean any contaminants.  That may not be an
issue for your application.

2010\02\08@144720 by Dario Greggio

face picon face
Alex Harford ha scritto:

> I think that is a good deal, I remember the prices on MAF sensors were
> quite high for my car, in the $300 CAD range.  But that is probably
> due to automotive ranges, and it had a burn-off circuit that heated
> the wire extremely hot to clean any contaminants.  That may not be an
> issue for your application.


yeah, I would just love to see this device's specs i.e. bar, flow qty
etc - and price :)


--

Ciao, Dario
--
Cyberdyne

2010\02\08@144733 by Michael Rigby-Jones

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face


> -----Original Message-----
> From: KILLspampiclist-bouncesKILLspamspammit.edu [RemoveMEpiclist-bouncesTakeThisOuTspammit.edu] On
Behalf
> Of Bob Blick
> Sent: 08 February 2010 18:41
> To: Microcontroller discussion list - Public.
> Subject: Re: [PIC] Measuring flow using a temperature sensor (and
maybe a
> heater)
>
>
> Back to the one that used two transistors heated to 50C. I built that
> many years ago when it forst appeared, because it was charming.
Although
> it does work, plain transistors are awful. There is too much thermal
> mass. It takes a minute to stabilize and response to changing flow
rates
> was wobbly.
>

I guess it would be somewhat better with small SM packages (e.g. SC70)?

Regards

Mike

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2010\02\08@144833 by Dario Greggio

face picon face
Bob Blick ha scritto:
>> Early this morning I've received an Offer by Sensortecnichs -
>> some 90EUR for a 0-5V sensor, capable of 1-2bar and 360 lt/hour.
>
> That's probably a good choice. It's hard to make an airflow sensor
> measuring low flow rates. Automotive MAF sensors are for hundreds of
> times as much air.

Yeah, I see..


> Back to the one that used two transistors heated to 50C. I built that
> many years ago when it forst appeared, because it was charming. Although
> it does work, plain transistors are awful. There is too much thermal
> mass. It takes a minute to stabilize and response to changing flow rates
> was wobbly.

This is a point indeed. I was planning on using a transistor as well,
coupled to a tiny SOT23 such as MCP9800. I can't actually think of
anything "faster" than a transistor to heat up, I mean... a lamp or a
resistor sounds slower to me...

--

Ciao, Dario
--
Cyberdyne

2010\02\08@150350 by Bob Blick

face
flavicon
face

On Mon, 08 Feb 2010 20:48:26 +0100, "Dario Greggio" said:

> This is a point indeed. I was planning on using a transistor as well,
> coupled to a tiny SOT23 such as MCP9800. I can't actually think of
> anything "faster" than a transistor to heat up, I mean... a lamp or a
> resistor sounds slower to me...

A hot wire exposed directly to the air is pretty responsive. The wire
material is also probably a relatively poor conductor of heat, so the
temperature is not heavily influenced by the connecting wire. As opposed
to a transistor, encased in plastic, with copper leadframe and
conductors muddling the accuracy by bleeding heat into the thermally
isolated parts of the device.

Cheerful regards,

Bob

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2010\02\08@152536 by Spehro Pefhany

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At 03:03 PM 08/02/2010, you wrote:

>On Mon, 08 Feb 2010 20:48:26 +0100, "Dario Greggio" said:
>
> > This is a point indeed. I was planning on using a transistor as well,
> > coupled to a tiny SOT23 such as MCP9800. I can't actually think of
> > anything "faster" than a transistor to heat up, I mean... a lamp or a
> > resistor sounds slower to me...
>
>A hot wire exposed directly to the air is pretty responsive. The wire
>material is also probably a relatively poor conductor of heat, so the
>temperature is not heavily influenced by the connecting wire. As opposed
>to a transistor, encased in plastic, with copper leadframe and
>conductors muddling the accuracy by bleeding heat into the thermally
>isolated parts of the device.
>
>Cheerful regards,
>
>Bob

The key to this kind of measurement is to maintain the temperature constant
and look at the power input. This is the same idea as
running a photodiode from a reference voltage into the virtual ground of a
transimpedance amplifier (keeping the voltage across the diode constant)
and thus eliminating most of the effect of the PD parallel capacitance.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spamBeGonespeffspamBeGonespaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



2010\02\08@160120 by John Gardner

picon face
> The key to this kind of measurement is to maintain the temperature constant
> and look at the power input.

That's how Bosch MAF system works - The one's I'm familiar with, anyway...

Jack

2010\02\08@161424 by Dario Greggio

face picon face
Spehro Pefhany ha scritto:

> The key to this kind of measurement is to maintain the temperature constant
> and look at the power input. This is the same idea as
> running a photodiode from a reference voltage into the virtual ground of a
> transimpedance amplifier (keeping the voltage across the diode constant)
> and thus eliminating most of the effect of the PD parallel capacitance.

I've been coming into this thought while considering the circuit.
I imagine the "left-off" sensor measuring 20°C, the other one measuring
50°C (coupled to "something") and, as the 50°C drip down to, say, 45,
you measure how much current you have to provide to make it 50 again


--

Ciao, Dario
--
Cyberdyne

2010\02\08@161533 by Dario Greggio

face picon face
Bob Blick ha scritto:
> A hot wire exposed directly to the air is pretty responsive. The wire
> material is also probably a relatively poor conductor of heat, so the
> temperature is not heavily influenced by the connecting wire. As opposed
> to a transistor, encased in plastic, with copper leadframe and
> conductors muddling the accuracy by bleeding heat into the thermally
> isolated parts of the device.

I see Bob.
I was considering a BD139-or alike, metallic case.
Since the sensor woudl be smaller (the aforementioned SOT), I should use
something else. Or maybe move to a TC74 (TO220) and use a BDX53 BJT.

--

Ciao, Dario
--
Cyberdyne

2010\02\08@164312 by Marco Genovesi

picon face

Maybe only a single sensor is needed?
-First, measure ambient temperature without heating the sensor.
-Then, apply a definite "slot" of heat to the sensor:  playing with max
temperature value reached and temp. decay time I think it is possible to
obtain the airflow speed. Probably a low-end 8 pin PIC with comparator is
enough for this.

ciao,
Marco





{Original Message removed}

2010\02\08@232128 by Richard Pytelewski

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face
The transistor body provides thermal mass, true.  However, it may be an
asset depending on the application and the range of temperatures and the
rate at which the temperature changes.  "Dithering" temperature sensors
making the electronics (and whatever they control) go on and off "quickly"
may not be the best for the application.  So quick response as an asset may
or may not be advantageous.  (Thought I'd stir up the pot a bit).  

In my experience thermal responses of several to tens of seconds have been
more than adequate.

Rich

{Original Message removed}

2010\02\09@044711 by Alan B. Pearce

face picon face
>Back to the one that used two transistors heated to 50C. I built
>that many years ago when it forst appeared, because it was charming.
>Although it does work, plain transistors are awful. There is too
>much thermal mass. It takes a minute to stabilize and response to
>changing flow rates was wobbly.

But using SMT transistors such as the MMBT range would reduce the mass, and
such packaging probably has a better thermal contact between the chip and
the packaging than something like a TO99 package.

2010\02\09@045210 by Alan B. Pearce

face picon face
>This is a point indeed. I was planning on using a transistor
>as well, coupled to a tiny SOT23 such as MCP9800. I can't
>actually think of anything "faster" than a transistor to heat
>up, I mean... a lamp or a resistor sounds slower to me...

Why use a seperate temp sensor? Can you not measure the Vbe drop to get a
measure of temperature? You already have connections to it. How absolute
does the temperature measurement need to be?

2010\02\09@171821 by Dario Greggio

face picon face
Alan B. Pearce ha scritto:
>> This is a point indeed. I was planning on using a transistor
>> as well, coupled to a tiny SOT23 such as MCP9800. I can't
>> actually think of anything "faster" than a transistor to heat
>> up, I mean... a lamp or a resistor sounds slower to me...
>
> Why use a seperate temp sensor? Can you not measure the Vbe drop to get a
> measure of temperature? You already have connections to it. How absolute
> does the temperature measurement need to be?
>


I'used to believe (and still am not sure) that I need 2 sensors - one
for "free air" and one for "coupled-to-heater" measurement, in order to
compare them and realize if a flow is going on...
And I2C is easier (and more accurate) than Analog and Vbe...


--

Ciao, Dario
--
Cyberdyne

2010\02\10@051618 by Dario Greggio

face picon face
more or less like this one
<http://www.lancier-monitoring.de/pdfdocs/doc_Produktinfo_FMA_200_C_engl.pdf>

(fyi)


--

Ciao, Dario
--
Cyberdyne


'[PIC] Measuring flow using a temperature sensor (a'
2010\03\22@221732 by Larry G. Nelson Sr
picon face
I have used thermistors in this application with good luck. The self
heating characteristics combined with the resistance relationship to
temperature works well.

Larry

At 12:21 AM 2/9/2010, you wrote:
{Quote hidden}

>{Original Message removed}

2010\03\23@023821 by Dario Greggio

face picon face
Larry G. Nelson Sr ha scritto:
> I have used thermistors in this application with good luck. The self
> heating characteristics combined with the resistance relationship to
> temperature works well.

yeah, thank you for adding your note Larry.
I'll work upon this in some months, I guess.

--

Ciao, Dario

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