UN-202: Gas USM (Measured density)
Description
Calculates the uncertainty in observed volume, mass, standard volume and energy flowrate for a gas USM. USM flowrate uncertainties are determined from an assessment of the meter calibration performance, installation and on-going performance/usage parameters. Density is determined from measurement and its uncertainty determined from the technical specifications of the densitometer used. Standard density and CV calculations and their uncertainties are performed using user-selectable calculations and the gas composition data. Pressure and temperature uncertainties are determined using the technical specification for the transmitters selected from the integrated transmitter selection tool.
General
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.
Input/Output
Options
The options section controls how the calculation is performed and dictates which inputs are required.
Pressure Units
This is the line pressure of the gas stream measured upstream of the Coriolis meter.
Note: 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.
The default value for Absolute Pressure is set to 1 standard atmosphere (1.01325 bar)
Station Uncertainty
By default, the module will calculate the uncertainty for a single metering stream. If parallel streams are selected the Station Uncertainty will be calculated assuming the metering streams are nominally identical and the flow is split equally between the streams in use.
Note: When selecting parallel streams the correlation between inputs has to be considered and the user is presented with a further option to control how the correlation is defined.
Inputs
Pressure
This is the line pressure of the gas stream measured. 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.
Number of parallel meters
This input is only visible when parallel streams are selected for the station uncertainty and refers to the number of in-use metering streams the flow is divided between.
Temperature
This is the measured temperature of the gas stream.
Velocity
The velocity of gas flowing through the USM.
Note: Ultrasonic meters operate over a specified velocity range, which is independent of temperature, pressure, or composition.
Density
The measured density of gas in the stream.
Outputs
The outputs section shows the calculated flow rate and uncertainty taken from the Flow Rate tab.
Calculation Blocks
The following blocks are used within this uncertainty module: