Running Calculations

All UNCERTAINTYPLUS calculations follow a similar structure and contain the following components.


The General tab contains header information which can be added to the uncertainty module. This is particularly useful if a record of the uncertainty calculation is to be saved or sent to another user. Information can be entered into a number of predefined fields such as a description, the site, system, date. Notes can be added to the module for the benefit of the user or any one else who will use the module or associated report.


The Input/Output tab is used to define global variables in the uncertainty module. These variables can be in the form of input values and options. The input values set here will be applied in multiple blocks (tabs as seen on the user interface) and are generally the process conditions and/or indicated flow rates. Options refer to the configuration of the metering system and hence the uncertaity module e.g. The number of DP transmitters used in an orifice plate or venturi meter stream.

Note that where more than one DP trasnmitter is selected only one will be insue at the differential pressure specified in the inputs. If uncertainty is calculated over a range of differential pressures the DP transmitter selected will be automatic based on the DP value and the switch point.

The outputs as calculated by the uncertainty module are displayed on this tab. These consist of the flow rates and their absolute and relative expanded uncertainties. The expanded uncertainty is automatically set at k = 2 so that the output uncertainty values exceed a 95% confidence level. The units of the outputs can be modified on the Input/Output tab. This will only apply on this tab and not to other tabs where the same flow rates and uncertainties may appear as units are fixed at block level.

Inputs and outputs can be set over a range of an input value as seen in the image below. Select the check boxes to choose which input and output(s) to calculate uncertainty over the input range. The number of repeats and the minimum and maximum values of the input range are required. The input values will be autogenerated, evenly spaced across the range when clicking the update button. The input values within this range can be modified by the user once the range is defined.

Uncertainty Blocks

Uncertainty blocks vary from module to module and more information on the configuration of individual modules and blocks can be found here?.

The different uncertainty blocks used in a module can be veiwed by switching between the tabs at the top of the module. Blocks are used to build towards an overall uncertainty in the flow across a metering system by calculating the uncertainty in individual elements such as the different instruments used and in calculated properties before combing these uncertainties to get an uncertainty in the flow rates. Common blocks include those for instruments such as pressure, differential pressure and temperature transmitters, densitometers and water cut meters, calculated properties such as density, standard density and calorific value, and blocks for different meter types.

In individual blocks there will be options to select and inputs to enter for the user, however those options and inputs will only apply to the individual block. The results will be presented in an uncertainty budget. The uncertainty budget consists of the sources of uncertainty and their expanded uncertainty, associated probability distribution and relevant divisor, standard uncertainty and sensitivity coefficient. Below the uncertainty budget(s) the value will be displayed along with its calculated standard absolute uncertainty, expanded absolute and relative uncertainties.


The results of a calculation can be presented in the format of a report which can be saved in pdf or xps file format.

If there are multiple DP transmitters configured if the DP value in the main input is above the range of the DP transmitter then the uncertainty for that transmitter will show as NaN. The DP transmitter block will produce an uncertainty if there are any ranged DP values within its span.


Saving Calculations

To save an uncertainty module, click the save button on the Home ribbon. If the module has not been saved this will take you to the standard Save As dialog which will let you save the file in any location with the UNCERTAINTYPLUS extension (*.unx). The save button will be greyed out if you open a saved calculation but will become active once the calculation has been changed or information added. An asterisk at the start of the calculation title indicates that the calculation has been changed or edited since it was last saved.