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nvp
Joined: 16 Sep 2003
Posts: 76
Location: EARTH
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 25 Sep 2003 6:17 AIR FLOW SENSOR |
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Hello Friends..
Does any one has idea HOW AIR FLOW SENSOR works? Also if any one has circuit , Let me know u have..
Regards
NVP
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sadat007
Joined: 01 Jan 1970
Posts: 411
Helped: 6
Location: Pakistan
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| 25 Sep 2003 7:04 Re: AIR FLOW SENSOR |
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| It can be like a fan with dc motor, or it can be two temperature sensors on effected by air flow one dose not.
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techie
Joined: 05 Feb 2002
Posts: 834
Helped: 42
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| 25 Sep 2003 12:36 |
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| Air flow sensor can be designed using 2 thermistors. One measuring the ambient temperature and the other is maintained at an elevated temperature. The power required to keep the temperature constant is related to the ambient temperature and the air flow over the thermistor.
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dudu
Joined: 04 May 2002
Posts: 6
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| 25 Sep 2003 12:40 Re: AIR FLOW SENSOR |
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| you can see some papers from TUDELFT, they have a fully integrated flow sensor now are availlable in the market.
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nvp
Joined: 16 Sep 2003
Posts: 76
Location: EARTH
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| 25 Sep 2003 12:42 |
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Hi Techie
Do u have any reference shematic of the same?
Yep, Why we need two thermisters? One is enoug right? Why can't we fix one as variable or fixed value resistor? Other one is thermistor.
Is that makes sence??
regards
NVP
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nvp
Joined: 16 Sep 2003
Posts: 76
Location: EARTH
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| 25 Sep 2003 12:46 Re: AIR FLOW SENSOR |
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| dudu wrote: |
| you can see some papers from TUDELFT, they have a fully integrated flow sensor now are availlable in the market. |
Can u pls send me some URLs
Regards
NVP
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wolf69
Joined: 20 Sep 2002
Posts: 117
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| 25 Sep 2003 13:21 |
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you can use ultrasoud too. in case of hot hair flow the two-termistor mode is not precise.
bye
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techie
Joined: 05 Feb 2002
Posts: 834
Helped: 42
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| 25 Sep 2003 18:03 |
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You need 2 thermistors because 1 is used to measure the ambient temperature since the power required to maintain the other thermistor at a constant temperature will be highly dependent on ambient temperature.
In order to maintain the 2nd thermistor at constant Temperature, you just have to measure its resistance and heat it up so that its resistance maintains a certain value.
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flatulent
Joined: 19 Jul 2002
Posts: 4856
Helped: 292
Location: Middle Earth
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| 25 Sep 2003 18:09 second order effect |
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The air humidity also controls the heat loss in the wind. If you want to be very accurate, you will also have to measure the humidity and make a correction for this.
The heat loss vs wind is very nonlinear. This method works best for low velocity. Use the propeller or anemometer (cups at the end of spokes) method for higher velocities.
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techie
Joined: 05 Feb 2002
Posts: 834
Helped: 42
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| 25 Sep 2003 18:15 |
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| Flatulent is right. The method I described is only usefull if the air-flow is quite low. This method is also not very accurate since humidity and non-linearity are both a factor to consider. But at these rates of flow, measurement using mechanical methods become very expensive or inaccurate. If you are measuring high wind speeds, better go for mechanical.
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purloiner
Joined: 24 Nov 2001
Posts: 16
Location: Here and there...
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| 25 Sep 2003 20:53 Re: AIR FLOW SENSOR |
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The method using two thermistors is referred to as Thermal Mass Flow and companies like Endress + Hauser make an exremely accurate instrument unsing this technology, called T-Mass...
It's used in application where the mass flow of a specific gas needs to be measured... As long as the device is calibrated the device can be programmed to any one gas but, it isn't possible to measure more than one different gas with one meter because, the thermal expansion coefficeints of the various gasses arn't always the same, actually they[re never the same...
Once the device has been calibrated and linearized for the specific gas, only moisture can affect its accuracy...
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Trishool
Joined: 12 Jul 2001
Posts: 78
Location: Himalayas.(mount K2)
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| 25 Sep 2003 22:11 Re: AIR FLOW SENSOR |
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Hi,
EdnMag , reed electronics articles are full at google do a little search . Basicall you require to heat some thermistor and when air flows over it you measure the resistance ! . But be carefull about ambient temperature you will also require one reference thermistor which in some designs you wont find .
good luck
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tonyfic
Joined: 09 Jul 2002
Posts: 15
Location: nyc, ny, usa
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| 26 Sep 2003 13:13 Re: AIR FLOW SENSOR |
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try this...it works
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techie
Joined: 05 Feb 2002
Posts: 834
Helped: 42
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| 26 Sep 2003 13:52 Re: AIR FLOW SENSOR |
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Thanks for the file but to conserve bandwidth, please avoid BMP file. The same file converted to GIF is only 18kb. Pls find attached
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Fragrance
Joined: 26 Jul 2002
Posts: 1313
Helped: 23
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| 29 Sep 2003 7:41 Re: AIR FLOW SENSOR |
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hi
here is the some thing from me air flow sensor programable type pic 16f84 based design with lot of paarameters may this also help you to design your own
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kib
Joined: 27 Mar 2003
Posts: 121
Helped: 7
Location: Bangalore, India
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| 06 Oct 2003 11:32 Re: AIR FLOW SENSOR |
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also check this application note.
may help u for design purpose
http://www.linear.com/pdf/an43.pdf
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kib
Joined: 27 Mar 2003
Posts: 121
Helped: 7
Location: Bangalore, India
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| 06 Oct 2003 12:05 Re: AIR FLOW SENSOR |
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also this one
http://www.analog.com/Analog_Root/sitePage/mainSectionContent/0,2132,level4%3D%252D1%26ContentID%3D17355%26level1%3D214%26level2%3D%252D1%26level3%3D%252D1,00.html
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nvp
Joined: 16 Sep 2003
Posts: 76
Location: EARTH
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| 06 Oct 2003 13:17 Re: AIR FLOW SENSOR |
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| kib wrote: |
also this one
http://www.analog.com/Analog_Root/sitePage/mainSectionContent/0,2132,level4%3D%252D1%26ContentID%3D17355%26level1%3D214%26level2%3D%252D1%26level3%3D%252D1,00.html |
Kib
U did Great Job!!!
Let me know if u get some more!!
Regards
Last edited by nvp on 07 Oct 2003 5:22; edited 1 time in total |
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chrhuy
Joined: 16 Dec 2001
Posts: 17
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| 06 Oct 2003 20:03 Re: AIR FLOW SENSOR |
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Not all systems work with resistors, if i am correct, the automotive
air flow sensors do not...
they work with a constant heating element and measure the amount of cooling...
A guy once told me, that some of them use a very thin wire, like a light bulb, so when they place a voltage onto it, it starts to glow, and with less or more cooling the resistance of the wire changes, and so they can measure the current flowing through it...
Don't know it for sure, but seems to make sense...
Hope this helps you a little..
Chrhuy.
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W49N3R
Joined: 23 Nov 2003
Posts: 3
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| 23 Nov 2003 6:51 Re: AIR FLOW SENSOR |
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It is imperative to understand exactly the environment where the sensor will be used.
There are different characteristics in each environment, and different sensors more appropriate for each one.
In most cases, measuring the diference in temperature (twin thermal elements), one exposed the other don't, is enough to measure how much heat was removed from the exposed, but it is not very linear and depends on ambient effect.
An effective way is by moving a rotor, but requires a certain volume of air to be someway more precise. Sometimes using two different techniques is better.
One should always remember that for the right job there is a right tool, same way here.
Wagner.
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darciok
Joined: 04 Apr 2004
Posts: 1
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| 20 Sep 2004 0:09 Re: AIR FLOW SENSOR |
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I found this...I think it's quite good circuit on pic..
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jduraan
Joined: 26 Mar 2005
Posts: 1
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| 26 Mar 2005 22:33 Re: AIR FLOW SENSOR |
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| I've checked the airflow sensor in a ford escort. it has two wires very close to each other. are the one used as a reference?
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szymex
Joined: 10 Apr 2005
Posts: 1
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| 10 Apr 2005 13:18 |
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| wolf69 wrote: |
you can use ultrasoud too. in case of hot hair flow the two-termistor mode is not precise.
bye |
I agree. I've done sth like that
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polymath
Joined: 02 May 2006
Posts: 231
Helped: 20
Location: England
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| 18 Jun 2006 11:02 Re: AIR FLOW SENSOR |
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have a look at most modern car engine management systems
the under bonnet environment is one of the most hostile electronics will encounter other than military - very high temp Δ, high G, high alititude Δ, very high electrical noise.
most systems use hot wire or ultrasonic Air Flow Meters and are electrically very robust, accurate, and normally have signal conditioning for 8-16V supply and 0-5V output.
save yourself time and effort and get one from a scrap vehicle and adapt it for your flow rate
good ones to use are Hitachi, Ford (Hitachi Clone) or Bosch
Polymath
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sinatra
Joined: 29 Mar 2002
Posts: 243
Helped: 12
Location: Neverland
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| 18 Jun 2006 13:42 Re: AIR FLOW SENSOR |
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Just a short remark.
Talking again about the heating type of sensor.
I had already seen types that just use a metalic pipe whee the gas or the liquid will be pssing.
Then there are3 windings outside the pipe, so that there is really no contact beteewn the "sensor" and the material we are measuring the flux.
The measurementas are just the electrical resistances of the first and the third winding.
The first winding measures the temperature of the gas o liquid before it is heated up.
The second winding is used to warm up the fluid.
The 3rd winding measures the temperature of the fluid after is was warmed up by the 2nd winding.
Using a whitstone bridge the resistances of the first and 3rd windongs are compared and the mass flouw is related to the temperature difference of the 2 sensosrs (1st and 3rd).
It is a completely non invasive method that can be used to measure mass flow of "aggressiv" fluid for examples.
Hope it helps.
S.
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Diksi
Joined: 06 Jun 2004
Posts: 16
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| 07 Dec 2007 12:14 Re: AIR FLOW SENSOR |
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| kib wrote: |
also this one
http://www.analog.com/Analog_Root/sitePage/mainSectionContent/0,2132,level4%3D%252D1%26ContentID%3D17355%26level1%3D214%26level2%3D%252D1%26level3%3D%252D1,00.html |
It was late but can You tell me what was on this link ?
Some alternative to see information from link?
Thanks!
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kender
Joined: 19 Jun 2005
Posts: 956
Helped: 70
Location: Stanford, SF Bay Peninsula, California, Earth, Solar System, Milky Way
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Diksi
Joined: 06 Jun 2004
Posts: 16
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| 10 Dec 2007 1:47 Re: AIR FLOW SENSOR |
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Tell me wich one You suggest to use ? TMP12 no more present .. Lm335 are one solution but in plastic case ...
Thanks for links!
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kender
Joined: 19 Jun 2005
Posts: 956
Helped: 70
Location: Stanford, SF Bay Peninsula, California, Earth, Solar System, Milky Way
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| 10 Dec 2007 2:42 Re: AIR FLOW SENSOR |
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| Diksi wrote: |
Tell me wich one You suggest to use ? |
I don't have a particulal preference. I would recomend implementing them with 2N2222 transistors in TO-18 (metal can) cases .
| Diksi wrote: |
| Lm335 are one solution but in plastic case ... |
LM335 is available in TO-46 case, which is a type of metal can.
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Fragrance
Joined: 26 Jul 2002
Posts: 1313
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| 11 Dec 2007 6:11 Re: AIR FLOW SENSOR |
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hi
this is another good idea using discrate component
regards
Fragrance
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