FT'S

A volumetric measuring flow meter measures the volume of a fluid in litres/min (say).

A mass flow meter measures the mass flow rate of the fluid in grms/min (say).

If you had a cylinder of air of 1 litre in volume at atmospheric pressure and temperature, and you pushed the air though each of the flow meters they would read the same at STP.

i.e. 1 litre = 3 microgrms (or whatever density air is).

If you filled the cylinder with 1 litre of air at twice the ambient pressure, same temperature and volume.

The volume measuring flowmeter would read somewhere in the range 1 to 1.5 litres depending on the type of flow sensor used.

But the mass flow sensor would read 2 litres or 6 micrograms etc... Which can be corrected for twice the pressure to show that the equivalent volume at STP is 1 litre.

I don't think I've described that very well - another coffee this morning is needed methinks!!

John.

The relationship between the two measures is the density of the material.

http://www.simetric.co.uk/si_liquids.htm

http://en.wikipedia.org/wiki/Density

The type of transmitter used in any particular case depends upon a number of factors and it is not possible to give a concise reply to the question.

For a perfect gas following Charle's and Boyle's laws there is a definite and fixed relationship.

For liquids and solids it is just basically the density of the material.

John.

Density is the key. There are approximately 10000 different flow meters that measure just about every different fluid on earth. Orifice plate, venturi, coriolis, ultrasonic, thermal mass, pitot tube, annubar, etc. What fluid are you trying to measure?

Volumetric flow meters require only the flow rate to be known to be able to work out the amount of material moved accross it. They have a fixed, known volume and therefore from a measured flow the cum/hr can be calculated. Mass flow meters measure the mass ( accounts for density changes)and velocity and as such can be a little more accurate than volumetrics if the final requirement is dependant on weight.