Diode Anemometer Circuit

[For The Popcorn]

Years ago I saw a simple circuit using a pair of diodes to make an thermal anemometer. Now that I have a need for one, my Google search powers are wearing thin.

I'm working on improving a laser cutter filter system, and one of the things I'm like to do is measure air velocity in the duct to detect filter condition. A thermal anemometer seems like a good way to go. It will feed into a PIC18F-series micro to some kind of indicator.

Has anybody got a simple circuit example?


My alternative is a differential pressure sensor across the filter. I can't say I see any great difference between the two approaches as far as telling when a filter is clogged.

 

[For The Popcorn]

What an insulting ass. Thanks for your awesome help.

 

[ZipZapOuch]

What an insulting ass. Thanks for your awesome help.

Help Vampire? Feel free to go away.

 

[BR-549]

Just search for diode anemometer. Take your pick. I used to work for a company that made diode anemometers for military runways. All over the world. In every climate.

 

[For The Popcorn]

Thanks for all the ideas and helpful(?) comments. As I said in post #9, I have a plan in place. I only posted again in post #10 to correct an error in my schematic.

I had already done extensive research into using a MAF sensor, but since the suggestion was made again, I took another look. Since I cannot find any datasheet on commonly available models, or any model for that matter, and back-of-envelope calculations suggest my flow rate will be much less than a V8 roaring down the freeway, a MAF sensor doesn't seem like a good solution.

I did learn that many of these things operate from +5 volts rather than the expected +12v (since they interface directly to the ECU), and may put out either a zero - 5v analog signal or a square wave with the frequency proportional to flow rate. Either of those would be ideal to interfacing with my system. But without a datasheet, I don't know if my flow rate fits in their dynamic range at all – darn, I wish I knew how to use Goggle! I wonder if NestscrapeNavyavitor would work?


Fortunately, despite my apparent lack of search engine skills on my Cricket phone (those big buttons are so wonderful!), my project is coming together rather nicely.

Perhaps Mr. ZipZapOuch will demonstrate his extraordinary search skills and produce a datasheet rather than continuing to demonstrate his keyboard warrior skills.

 

[ZipZapOuch]

I posted a datasheet and I can't help that you can only assume a MAF only works on V8 engines - I guess you really limited it to

V8 roaring down the freeway

Since electronic ignition systems and fuel injectors are on a lot of engines besides V8s (all the way down to small motorcycles and portable generators) and those engines have a wide range of RPM from IDLE to redline, I really don't want to share my datasheet search results that were easily found when common manufacturer names and model numbers are included in the search (as I instructed above) - I'm afraid that, once I pay for the datasheet for you, that will be just the beginning of your nagging for me to help since you are only giving a half-hearted effort to find a datasheet and you're even unwilling to sign up for a 30-day free trial to get a datasheet. I'm out.

Dealing with, as you call them in your signature line, "help Vampires", is just too much work. I'm just your alternative solution will be much better than the hackish technology of MAFs.

 

[For The Popcorn]

Put up or shut up. It's pretty much that simple. You claimed finding a MAF datasheet was a simple task – I find this to be untrue.

As to whether I'm a "help vampire", geez on grief. I have actually asked questions on this forum maybe half a dozen times.

 

[ZipZapOuch]

Put up or shut up. It's pretty much that simple. You claimed finding a MAF datasheet was a simple task – I find this to be untrue.

As to whether I'm a "help vampire", geez on grief. I have actually asked questions on this forum maybe half a dozen times.

I did put up, then you changed the request to say it had to be free. Then I told you it is free - you just have to register for a trial period. So sad for you that you cannot be happy or too broke to sign up for a trial period.

 

[ZipZapOuch]

You claimed finding a MAF datasheet was a simple task – I find this to be untrue.

I could imagine that it can be quite challenging for some people - but it was simple for me.

 

[For The Popcorn]

Despite claims to the contrary, MAF sensor datasheets aren't common on the web. But I did find this airflow vs output graph for a Bosch MAF in one of the car groups.

So now I have something to work with.

Air is being pulled through the laser cutter and filter system by something akin to this dust collector blower, rated at 1550 CFM. It's not my equipment, so I don't know the exact blower, but I'm told it's something like this.

Converting 1550 CFM to airflow in kg/hr is a flow rate of about 3100 kg/hr maximum, but I suspect it will actually be significantly less through the laser cutter and filters.

So my airflow is off the top of the MAF sensor chart, yes? Not so fast. In a MAF sensor, the entire airflow is directed through the sensor, which is in around a 3.5" diameter tube. That's an area of around 10 in. sq.

My measurement point is in front of a 6" hose opening into a 20" x 20" area in front of a filter. The area of a 6" hose is about 28 in. sq.

If I position a sensor of this type in the center of the air flow at the transition from the 6" home, the sensor will be exposed to a small fraction of the total air flow.

But I think I am thinking of this wrong. I'm not specifically looking for mass air flow (which is volume). I'm looking for velocity to gauge whether a filter is clogged or air flow restricted in some way (or airflow is higher than normal due to leaks or operating without filters).

So back to the Bosch graph. Max rate is 450 kg/hr, with is approximately 900 CFM. The area of the MAF sensor is about 10 in. sq., so according to a handy on-line calculator, that about 68 m/s linear velocity (excuse the switching of units, the numbers are more manageable). Through my 6" hose at 1550 CFM, the linear velocity would be about 40 m/s, about 60% of the MAF rated flow. I'm taking a WAG that the actual flow will be more like half that or less, which for this particular MAF sensor gives me an output range from 1 – 3 volts.

Maybe it is doable. I'm still tending towards a DIY approach so I can adjust gain as needed, but the MAF sensor may warrant some investigation.

 

[ZipZapOuch]

There you go! Way to apply yourself and add the word "Bosch" to your search as I told you way back in my first instructions of how to use Google. I'm happy for you.

 

[For The Popcorn]

I refer you back to post #21, to which I will add the word condescending.

 

[ZipZapOuch]

I refer you back to post #21, to which I will add the word condescending.

Oh, without my management skills, you would have dropped the MAF option all together. Any unmotivated person can be encouraged to get something done - it just takes a manager who understands what makes a particular person want to complete a task. Looks like I found the trigger(s) that motivate you.