Airflow Sensor in Product 4

[Maxham1]

We're looking for an airflow sensor that we can install in our product (power supply). Instead of measuring the rotation of the fan with a Hall-Effect sensor, one of our customers has asked that we consider a sensor that can directly measure the airflow either immediately in front and behind.

Although I'm familiar with using airflow sensors for design and testing, like hot-wire anemometers, I would like to know if there are product-based sensors, ideally something off-the-shelf, that we can install in our product. We're not looking for accurate flow-rate measurements, but instead we would like to ascertain in the fan is on or off.

Any suggestions would be greatly appreciated.

 

[MadMango]

Vane operated air flow switch?

http://www.dwyer-inst.com/Products/TOC.cfm?MainCategory_ID=2&iCurrentCategoryID=304

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of these Forums?

 

[Maxham1]

Thanks for the info MadMango. I should have mentioned that we're looking for a miniature version, something that would fit in front (or back) of a 2 inch diameter fan. I check around on the dwyer website to see if there's anything smaller.

 

[itsmoked]

I am really surprised you don't do what everyone else does and just add the proper dash or letter to your fan to get the rotation pulses out of it. Why reinvent the wheel here and at a higher price no less?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Maxham1]

Yes, I love those proper dashes and letters as much as the next engineer. The decision in this case is being made by the customer to explore a belt and suspenders approach - go figure.

 

[HDS]

You could use a pressure sensor. Some which can be very cheap. If you are ambitious use a differential sensor to look at the drop across the fan.

You could use the mass air flow sensor from the intake of a car.

Like itsmoked implied you shouldn't need a hall effect sensor if you have a 3 wire fan that outputs it's RPM.

 

[itsmoked]

What exactly are you going to do with any output signal?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Maxham1]

Thanks HDS. Looks like the wind is changing direction and we're leaning towards a hall effect sensor. HDS, you mention that we shouldn't need a hall effect sensor if we have 3 wire fan that outputs its RPM. That sounds interesting.

Keith, what exactly are we going to do with any output signal you ask. Probably feed it to some control board. That's where our EE's take over, so it's something I'm not tasked with.

BTW, it looks like we're going to use a Rotron Propimax 2 fan with an FPS (failed performance sensor). We currently use the same fan, sans the FPS, in our product.

Any and all advice and comments greatly appreciated?

 

[itsmoked]

Now I'm really confused. Early on I suggested just using a fan with a rotation sensor like every fan in a PC these days. Getting the rotation option as I mentioned costs a few pennies since a gazillion are used every year.

If the design is rational, then if the fan is turning, you will have airflow. Every PC motherboard has this feature on multiple fans. All you need to do is monitor the pulse train. If the frequency coming out is higher than some minimum then you have cooling. You will find no less expensive a solution. If you products that need this already have fans, you will still be better off replacing them with identical pulse output models, than with designing some add on scheme.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Maxham1]

I think the difference may be that we currently use AC fans and I don't think that they don't generate a pulse train that could be measured. I usually ask for help with the electrical issues from the electrical engineers, which I'll do in regard to whether our fans currently provide a pulse train.

Thanks,

Dave

 

[Maxham1]

I meant to write above "I don't think that they [AC fans] generate a pulse train that could be measured."