Wet Gas Venturi (Calc Dens, Calc Std Dens,Calc CV)


Calculates the uncertainty in the corrected gas mass flowrate from a Venturi encountering a wet gas flow, using a “Chisholm De Leeuw” based wet gas correction. Mass uncertainty is based on “dry gas” uncertainty (as per Module 321) in addition to wet gas parameters and their uncertainty. 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.



This is the line pressure of the gas stream measured upstream of the Venturi meter. 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 Venturi meter. 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 option is only visible when multiple transmitters are selected and controls the selection of the transmitter which is deemed to be in-use for calculating the uncertainty. The switch Point is expressed as percentage of the span of the low transmitter. Consider the example where two transmitters are used; the low range transmitter has a range of 0 mbar to 125 mbar and the high range transmitter has a range of 0 mbar to 500 mbar. Setting the switch point to 95% will use the high range transmitter when the differential pressure is above 118.75 mbar (95% of the low range transmitter span)


This is the measured temperature of the gas stream.


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

Calculation Tabs

The following tabs are used within this uncertainty module:



Differential Pressure



Standard Density

Calorific Value

Wet Gas Venturi Flow rate