High Precision Flow Meter

Uh, how accurate? (By the way, liters per minute is not a unit of mass flow rate)

Right now, I have an Omega FMA 5400/FMA 5500 Mass Flow Controller which is accurate within +/- 2%. I would an accuracy within 0.5% for my application. This particular meter uses temperature gradient to measure the flow rate. The liters per minute can be converted to a mass flow rate based on the density of the gas being measure. I actually just need the volumetric flow rate.

The liters per minute can be converted to a mass flow rate based on the density of the gas being measure

Measuring density of gas is not so easy. Everything depends upon pressure and temperature.

You may try Krohne Vortex meter, where these compensations for pressure and temperature for specific gas or steam are available built-in.

As with other thermal type meters, this meter measures mass flow rate, as its name implies. If you keep mass flow constant but vary the temperature and/or pressure the reading does not change.

You say you actually just need the volumetric flow rate. Presumably this is volumetric flow referred to some specified standard temperature and pressure conditions (typically in US 60°F, 1 atm = 14.7 psia) so is equivalent to mass flow. To calculate volumetric flow, you don't need to know density at actual flowing conditions, only at the standard conditions. If it's already calibrated in standard litres/minute you don't even need that.

If I remember right +/- 2% is about standard for this type of meter. Might be worth trying Coriolis type. Just found on web one from Krohne which says accuracy on gases +/- 0.5%, but you'd need to check just what that means.

Cheers.........Codey

Presumably this is volumetric flow referred to some specified standard temperature and pressure conditions (typically in US 60°F, 1 atm = 14.7 psia) so is equivalent to mass flow. To calculate volumetric flow, you don't need to know density at actual flowing conditions, only at the standard conditions. If it's already calibrated in standard litres/minute you don't even need that.

If mass flow rate is kept constant and the pressure and temperature is specific standard conditions, then the (if calibrated) the volume flow rate shown will be correct. But, if the actual working temperature and pressure is not specific standard reference condition, the volume will depend up on the actual temperature and pressure, even though the mass flow rate is constant. If pressure is more than standard conditions, for same flow rate volume flow rate will be less. If pressure is less than for same mass flow rate volume flow rate will be more.

As there is specific relation between volumes of specific gas at various temperatures and pressures, in compensated flowmeter, along with the mass flow rate, temperature and pressure are measured. The density is calculated based on actual temperature and pressure for specific gas, and then the volume flow rate is indicated.

But, if the flow meter is not the compensated one, the volume flow rate will not be available (or it will be wrong)

That's broadly correct, but the point I'm making is that usually you don't want the volume flow at actual conditions, you want it at standard conditions (SCFM in usual US units). A thermal or Coriolis flowmeter gives mass (or standard volume) flow direct, so if this is what you want you're OK. If it's an untypical case and you want actual volume flow a calculation based on measured temperature and pressure is needed.

For a ΔP type flowmeter, a calculation is needed to give either actual or standard flow, if temperature and/or pressure differ from calibration figures. Can either be manual, or measured values can be input to a PLC. In practice, if the temperature and pressure are unlikely to vary much, can choose calibration data in mid-range, and ignore variations. A calculation will show whether the resulting error is acceptable.

Cheers.......Codey

A thermal or Coriolis flow meter gives mass (or standard volume) flow direct, so if this is what you want you're OK.

Yeah, I would like to stick with this type of flow meter for the reasons you have mentions. I have checked out some of the suggestion and have been able to find a more precise one.

Thanks

You are correct Codemaster for cases you mentioned.

But, probably I could not make my point clear in y earlier post. I will try again.

If meter has no compensation, it will measure mass flow rate at actual working conditions. To find out volume flow rate it will assume density as at mean specified pressure and temperature range around standard temperature and pressure. Calculated volume flow rate is indicated, which will be actual mass flow rate / density at standard temperature and pressure.

On the other hand if meter is temperature and pressure compensated, it will indicate volume flow rate = actual flow rate / actual density at actual temperature and pressure. Now, it can indicate actual volume flow rate as well as calculated volume flow rate at standard conditions. Normally it will indicate calculated volume flow rate at standard conditions. But because of compensations, in this case observation will be more near to correct value

Yamatake make a great range of flow meters. I have used them for years, very good.

Alternatively try Bronkhorst.

You need to specify the precision required.

BTW you want accurate or precision meter? Both things are totally different.

Hi,

You might want to try these. Flow the links below

http://www.red-y.com/en/products/smart/index.html

http://www.bronkhorst.com/en/products/gas_flow_meters_and_controllers/

Here's one. (usual disclaimer)

hi, you can check with endress+houser mark. they have great equipments for this application and provide assistance for you.

alicatscientific.com