Flow switch!

[glowing]

I have been having a really hard time with a problem on site. We presently use a paddle wheel style flow switch for HVAC/ventalation low flow indication. I strongly dislike these unreliable and hard to set up switches.

I have been tempted to go toa 3/4 four wire velocity/flow transmitter, but know that the costy of this will get squashed. Instead, I have been looking into thermal switches. There are many of these on the market at decent prices, but it appears they are all 3/4 wire devices.

Needless to say, I do not want to spend a small fortune running new cable for 100 switches. I really want to get away from switches with moving parts, and thought thermal was the answer.

Does anybody know of such a 2 wire device? Are there any other suggestions?


Any input on this one would be extremely welcome. I have been doing a lot of diffing on this, all to no avail!

 

[cbarn24050]

Hi, some time ago I made a PIC based airflow sensor. It could be made into a 4-20mA device I guess.

 

[itsmoked]

There are "no moving parts" anemometers that are heated wires or ultrasonic whistle based.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[drtimnjoe]

What type of paddle wheel switch are you using? I know of a company that specializes in custom thermal flow measurement. try intekflow.com


Dr. Tim and Dr. Joe
Flow Measurement and Steam Surface Condenser Professionals

 

[nbucska]

The simplest would be a thermistor based anemometer

Plesae read FAQ240-1032
My WEB: <

http://geocities.com/nbucska/>

 

[glowing]

I realise a thermistor is the way to go, but am trying to stay with a 2 wire device, as I do not really want to spend 160k rewiring these installs

thanks for the feedback though

 

[cbarn24050]

Hi Again, I have a device that could be modified for you but this site wont allow me to send you the details. If you repost your question on

http://groups-beta.google.com/group/sci.electronics.design/topics

I can send you something.

 

[FrancisL]

Re "this site wont allow me to send you the details."
I have never had that problem. You can put net url links in with no problem.
What is the problem that stops you?

 

[cbarn24050]

Hi Francist, the information doesn't have a URL.