Calibration of Liquid Density
Meters at Combined
Temperature & Pressure
Calibration Stand Update
Tony Wright
Customer Services Manager
Agenda
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Background
Project requirements
Calibration Process
Current status
Test plan
New equations
Calibration approvals
Calibration of customer’s 7835’s
Summary
Emerson Confidential Slide 2
Background for New Calibration Strategy
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DECC (Department of Climate Control) in the UK requested all densitometer manufacturers
and Oil companies in the North Sea to launch a project “JIP” (Joint industry project) to
understand the behaviour of temperature and pressure effects on Liquid Densitometers and
to develop a new calibration strategy.
TUV NEL ltd, as an independent calibration facility, were contracted to test and validate
Liquid Densitometers at combined temperature and pressure. The calibration facility used 4
transfer standard fluids across the temperature range from 20⁰C to 100⁰C and from
atmospheric pressure to 100 bar.
From the NEL testing, it was concluded that there is combined pressure and temperature
effect during elevated temperature and pressure operating conditions which need to be
taken into density calculations.
DECC then released an instruction stating that Liquid Densitometers should be calibrated at
their anticipated operating conditions, i.e. simultaneously at temperature and pressure, using
one or more transfer fluids, the density of which has been determined across the required
temperature and pressure range with an uncertainty not exceeding 0.01%, directly traceable
to national standards.
Emerson Confidential Slide 3
Project Requirements
• Objective and Scope
– Provide a production calibration stand(s) for combined
temperature/pressure density calibrations.
• 3 different fluids:
– Silkospark (current Slough calibration fluid [machining fluid] ~ 825
kg/m3)
– Sebacate (~960 kg/m3)
– Sodium Bromide – (~ 1400 kg/m3)
• Combined P+T for two fluids (Silkospark, Sebacate) at
– 20°C – 0,50,100,150 bar
– 80°C – 0,50,100,150 bar
• 20°C at 1 bar A calibration on Sodium Bromide (stand to be
capable of combined P+T if required)
• Double capacity of current calibration stands
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Calibration Process Flow
Steve/Bob to provide flowchart of calibration steps for various options
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New Stands Schematic Overview
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Current status
• Original promise date July 2011
– Slippage due to:
• Damage in shipping
• Design changes during testing
• Pressure test rig commissioned
• Cleaning station commissioned
• All calibration stands fully functional
– Modifications completed
– Testing and commissioning re-started
• Similar system under test in MMI Boulder
Emerson Confidential Slide 7
Pressure Test and Cycle Hydro Stand
• Hydrostatic pressure test rig
• Rig will be used on all new and
repair 7835’s to:
– Pressure test each sensor to 1.5
maximum operating pressure
– Pressure cycle each sensor for 30
times to maximum operating
pressure
Emerson Confidential Slide 8
Cleaning Station
• Designed to flush out calibration fluids
• Up to 3 x 7835’s each cleaning session
• 3 stage cleaning process
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Liquid Density Calibration Stands
Combined Pressure and Temperature
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Test Plan
• Stability and repeatability tests on distilled water
• Change water to calibration fluids
– Repeat stability and repeatability tests
– Monitor for cross contamination
• Validate calibration results against
– Engineering Dept combined P+T calibration stands
– Current production calibration stands
– UKAS laboratory (also monitor contamination of fluids)
• Send fluid samples to external UKAS Laboratory
to determine effect, if any, of contamination
Emerson Confidential Slide 11
New Density Equations
• All major flow computer manufacturers contacted
• Existing format certificates will continue to be
available for limited pressure and temperature
ranges
Optimum Solution
New calibration stands
Dp = Dt * (1+K20*(P-1)) + K21 * (P-1)
K20 = K20A + K20B*(P-1) + K20C*(P-1)^2
Equations
K21 = K21A + K21B*(P-1) + K21C*(P-1)^2
Dpt = Dp * (1+K22*(t-20)*(P-1)) + K23*(t-20)*(P-1)
K20A,K20B,K20C,
K21A,K21B,K21C
Calibrate on new calibration stands on 2 fluids at 20°C for each unit
K22, K23
Calibrate on new calibration stands on 2 fluids at elevated t&P for each unit
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Calibration Approvals
• Our current ISO17025 (UKAS) calibration
laboratory has been in operation since 1981
– 20 Deg C and 1 Bar A
• Will apply for ISO 17025 for new stands
– Traceability through current UKAS Laboratory
– Liquid P+T via 3rd party approved laboratory
• Planned schedule for approval application is 6
months from release of calibration stands
• On receipt of approval, we will apply for MID
approval using new stands
Emerson Confidential Slide 13
Re-calibration of Installed 7835’s
• All installed 7835’s can be re-calibrated on the new stands
to DECC requirements
• 7830’s are not supported
• Fiscal (Micro Motion business partner) has built and
installed a new 7835 cleaning facility
– Operational from December 2012
• Over-check to include air-check and detailed visual
inspection prior to despatch to MMI Slough
Emerson Confidential Slide 14
Summary
• Functional testing of complete system has
started
• Calibration stands will be fully commissioned by
mid January 2013
– Existing stands will then be decommissioned
• Stands are designed to fully comply with DECC
requirements
• Plan to have new calibration stands approved to
ISO 17025 by mid 2013
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