This block calculates the uncertainty in density measured by a specified density transducer. The appropriate densitometer or coriolis meter should be selected from the drop down boxes and other inputs should be entered as per data sheets.
The densitometer or Coriolis meter manufacturer, model and range are selected from the drop down boxes.
In this section, a wide variety of inputs are given based on KELTON’s experiences.
If density is measured using a densitometer or Coriolis meter select calculated, otherwise select user entered to enter the estimated expanded uncertainty in the measured density.
Select the Manufacturer of the densitometer or Coriolis meter from the given list.
Select the Model of the densitometer or Coriolis meter.
Select the Range (If Specified by the manufacturer data sheet)
The densitometer or Coriolis meter characteristics are inputted from the manufacturer’s data sheets.
The uncertainty in the calibration reference of the density transducer.
Maximum tolerance allowed during calibration process. (Taken from calibration records where available, assumed otherwise).
Note: Typical value is between ± 0.05% of span to ±0.15% of span.
Average drift observed or expected between calibrations. (Taken from calibration records where available, assumed otherwise).
Note: Typical value is between ± 0.05% to ±0.15% of reading.
Temperature at which meter was calibrated. For coriolis meters the temperature effect can be corrected out in the coriolis transmitter or flow computer using the manufacturer’s specified pressure compensation. If this is done then the line temperature value should be entered here.
Pressure at which meter was calibrated. Difference in process pressure between calibration and operation. For coriolis meters the pressure effect can be corrected out in the coriolis transmitter or flow computer using the manufacturer’s specified pressure compensation. If this is done then the line pressure value should be entered here.
Uncertainty due to installation effects such as vibration, insulation levels, etc.
Note: a typical value would be 0.1%.
Uncertainty due to frequency signal conversion.
Note: a typical value would be 0.01%.
When a transmitter is selected, the relevant uncertainty components from that transmitter’s specification sheet are used for the uncertainty calculation.
The measured density value for which the uncertainty to be calculated is taken from the Input/Outputs tab.
The uncertainty calculation is detailed in the uncertainty budget table giving a break down of how the overall uncertainty is calculated.
Uncertainties associated with these values are taken in as the Expanded Uncertainties. The Standard Uncertainty is calculated from dividing the Expanded Uncertainty by the coverage factor which is determined by the probability distribution that best suits that uncertainty component.
The standard uncertainty is then multiplied by the sensitivity value then squared. This is done for each parameter that contributes to the overall uncertainty in the measured density. The Standard Uncertainty in the measured density is the square root of the sum of each component variance as shown in the following equation:
The Expanded Uncertainty is the Standard Uncertainty multiplied by the coverage factor (k). The coverage factor is defaulted to k = 2 (equivalent to a confidence level of approximately 95%).
The Relative Uncertainty is the Expanded Uncertainty divided by the measured density.
ISO 5168:2005 – Measurement of fluid flow – Procedures for the evaluation of uncertainties
ISO Guide 98-3 – Uncertainty of measurement – Part 3: Guide to the expression of uncertainty in measurement (GUM:1995) (2008)
Density transducers are available for selection from the following manufacturers: