Differential pressure velocity to air flow

It's been a while since I've done the calculation but to determine the airflow velocity (rough measurement only) do I use the following formula:



(Differential pressure + ((Differential pressure)^0.5))/2



Background:



I bought a 0-5 psi differential pressure sensor and an IC that converts the raw mv signal from the sensor into a 4-20mA signal, which I then send back to my PLC. I'm trying to get a rough representation of the airflow through a pipe. The pipe size is 1" and the orifice that I had my maintained team fab up is 1/2 inch.

Shane
OK so you have a dP guage with an electrical output.
I hope the factory literature discusses this idea.
IF you put the HP side of the dP gage to a pitot tube pointed INTO the air flow (gets total pressure) and you put the low side of the dP gage to the side of the pipe to get you static pressure you will now have the dP gage reading velocity pressure (VP) ie VP = TP - SP.
NOW you have to use the VP value to get velocity. I forget the formula but you should be able to get it from ASHRAE or ACGIH Handbook of Industrial Ventilation. Let me know if formula is V = VP x sqrt 4005.

Dan Bentler