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Flow meter with pressure and temp compensation
Dont understand pressure compensation requirement

In the nickel refinery fluid bed reactor I'm working on, there's a volumetric flow meter VERIS Verabar V510 (element) with a SMAR LD301 remote mounted transmitter.

The process gas being measured is compressed air. I understand why the temperature compensation as density of air changes with temperature and hence so does volumetric flow.

But why is there pressure compensation incorporated into this flow measurement?

Thanks

By Roy Matson on 24 July, 2009 - 11:52 am

Density also changes with pressure.

so volumetric flow meters don't require temperature/pressure compensation, only when the pressure and temperature of the process remain constant?

Theoritically if the Pressure and Temperature remain constant, Pressure and Temperature can be neglected but in the nature of gas, Pressure and Temperature will not be constant (effected by environemt and affected by process condition).

Furthermore, Verabar is a Pitot Tube type of Flowmeter which fall under pressure differential type of measurement. So I would say that P&T transmtter is compulsory for the Volumetric Flow measurement.

By anynomous on 30 July, 2009 - 7:10 am

Boyle's LAW -

PV=nRT

enjoy

Let's start at the beginning.

Let's assume you want to know the volume flow rate. The instrument you have reports rate of flow in volume units. Temperature and pressure may well affect the density such that for the same volume flow rate the mass flow rate will differ according to the temperature and pressure.

However, you need also to consider the effect of temperature and pressure on the flow instrument. For example, increasing temperature will cause the instrument to expand and in expanding it will contain a larger volume of gas.

The same is true of pressure, the pressure will cause the meter to expand slightly and contain a larger volume of gas.

Thus, 1 cubic meter of gas measured at low temperature and pressure is recorded as 1 cubic meter but at a higher temperature and pressure that same 1 cubic meter of gas may be recorded as slightly less than 1 cubic meter.

Therefore the flow meter may itself require correction for temperature and pressure effects even if it is measuring only the actual volume flow.

Therefore, when considering temperature and pressure effects it isn't simply a case of the effect on density (liquid or gas) but the effect on the sensor.

Pressure will also change.

Can anybody tell me the calculations for pressure and temperature compensation using any example?

Density is function of both pressure and temperature...