UN-305: Wet Gas Orifice(Calc Dens, Calc Std Dens, Calc CV)


Calculates the uncertainty in the corrected gas mass flowrate from an orifice plate encountering a wet gas flow using the wet gas correction described in ISO TR 12748. Mass uncertainty is based on “dry gas” uncertainty (as per Module 301) in addition to wet gas parameters and their uncertainties. Standard density and energy flowrate uncertainties are also estimated from this corrected gas mass flowrate. Pressure, temperature and differential pressure uncertainties are determined using the technical specification for the transmitters selected from the integrated transmitter selection tool.


The General tab is used to enter information, which is saved along with the uncertainty calculation and included in reports which are generated.

The tabs used for inputting data and calculating the uncertainty in the individual components of the uncertainty can be seen along the top of the module window.

The report tab is only visible once the calculation has been run and will not be visible if any parameters are changed until the calculation has been run once more.


The options section controls how the calculation is performed and dictates which inputs are required.

DP transmitters

This option is used to select the number of differential pressure transmitters which are used in parallel. If two transmitters are selected an additional Differential Pressure will be displayed so that information can be entered on both high and low transmitters. If three DP transmitters are selected a third Differential Pressure tab will be included for the mid transmitter.

Pressure units

This section gives the option of entering the pressure as either an absolute value or as a gauge value with reference to atmospheric (barometric) pressure. If Absolute is selected inputs are required for Absolute pressure and Atmospheric pressure and if Gauge is selected inputs are required for Gauge pressure and Atmospheric pressure. This ensures that whichever is chosen both the gauge and Absolute pressure value is available to other sections of the module.

Note: Gauge pressure is equal to the Absolute pressure – the Atmospheric pressure.



This is the line pressure of the stream measured upstream of the orifice plate. As described above, if Absolute is selected inputs are required for Absolute and Atmospheric pressure and if Gauge is selected inputs are required for Gauge and Atmospheric pressure.

Differential Pressure

This is the differential pressure measured across the orifice plate. If multiple transmitters are used the appropriate transmitter will be selected based on the transmitter ranges and the DP transmitter switch point.

DP Transmitter Switch Point

This options allows you to enter the percentage that shows the relation between the input over the span where the DP transmitter will switch to the higher transmitter.

Note: this input is available if more than one DP transmitter is selected from the options.


This is the measured temperature of the stream.


The outputs section shows the calculated flow rate and uncertainty taken from the Wet Gas Orifice Plate .

Calculation Tabs

The following tabs are used within this uncertainty module:



Differential Pressure


Calculated Gas Density

Calculated Gas Standard Density

Calorific Value

Wet Gas Orifice Plate