Industrial Automation Magazine India

Primary Standard Liquid Flow Calibration System

Published on : Friday 11-10-2019

Periodic testing and calibration of Water Meters/Process Flow Meters is extremely important when viewed against a set of deterrents like:
•    Prohibitively high cost of ownership/requirement of high kW power (to drive the pumps) and large quantity of water as also the large floor space requirement of conventional flow calibration systems, as well as,
•    The high cost, hardship and delays in sending flow meters to third party calibration laboratories.

Compared to fewer number of flow meters to be calibrated, Nagman has developed a cost effective and compact System/Rig – which also consumes much less Power/Water – and can calibrate a variety of water meters/process flow meters in quick time, either at the laboratory or at remote site locations in industry – expanding on the capabilities of their ‘Compact Piston Prover’.

What is a ‘Compact Piston Prover’?
The Compact Piston Prover (CPP) volume displacer Primary Liquid Flow Meter Calibration System (PLFCS) is the ideal solution for applications where highly accurate flow meter calibration is required. This system offers a combination of high performance, efficiency and convenience.

Exceptional accuracy, repeatability and stability are achieved by using a precisely honed stainless steel/steel cylinder with a matching piston assembly. Precisely known volume (please refer chart) displaced by this piston cylinder assembly – each and every time – becomes the ‘reference’ for ‘calibration’.

Time duration of the (known) ‘displaced volume’ from the piston cylinder assembly is precisely set and controlled by the pneumatically/hydraulically/electrically operated ‘actuator/servomotor’ which drives the piston. Based on this time duration controlled positive displacement (LPM or LPS) operating principle, this CPP quickly and accurately calibrates practically any type of flow meter, at various flow rates.

Temperature and Pressure corrections are employed to compensate for the effects of outside influences on the CPP flow chamber, the flow meter under test as well as the calibration fluid.

Calibrations through this CPP are practically immune to fluid viscosity, density and compressibility.

‘Compact Piston Provers’ available globally offer calibration uncertainties up to 0.02% but are prohibitively expensive and beyond reach of most industrial users.

Recently Nagman developed and introduced Compact Piston Provers (that offer up to 0.02% uncertainties) at more affordable prices but still beyond budget for the industries with limited number of flow/water meters installed!

To meet this demand, Nagman worked further to develop a complete range of these Compact Piston Provers with lower yet acceptable uncertainties – typically 0.08% – (CPP-E) – but at much lower cost of ownership, bringing these systems closer to the reach of these industries.

Integrated ‘primary standard liquid flow calibration systems/rig’
Nagman further went on to evolve an innovative concept to integrate these lower cost CPPs (CPP-E) with conventional yet compact (flow calibration) Test Beds to offer these industries – an affordable ‘primary standard liquid flow calibration system/rig’, meeting the industries’ limitations in water/power and space, and above all, at affordable cost of ownership!

This Test Bed can be designed to have up to 3 independent test lines to suit the flow/water meters to be mounted (and calibrated) typically:
•    Line 1: Water meters (up to 5) (accuracies up to 0.25%)
•    Line 2: Process flow meters (like EMF, PD, turbine) (up to 2) (accuracies up to 0.1%), and
•    Line 3: Coriolis mass flow meter (1 only) (accuracies up to 0.05%).

Customisation of the Test Bed, to suit customer requirements is achievable – on request.

Standard models

a) CPP (E) – Compact Piston Prover – Economy Model
For those customers who already have ‘Calibration Test Beds’, CPP (E) with uncertainty better than 0.08% can be supplied as ‘Stand Alone Unit’ for customer integration at site. CPP (E) is available in 3 flow rate capacities to suit flow meter line sizes from DN 6 up to DN 150. CPP (E), normally used with water media, can also be designed for use with ‘EXXOL’ media, which will help customers to use it for calibration of diesel/fuel oil flow meters.

b) PLFCS-TB – The PLFCS-TB model is CPP (E) integrated with a test bed with up to 3 independent lines as described above, to suit calibration of water meters/process flow meters/Coriolis mass flow meters, etc. The choice of CPP (E) model and design of test bed can be based on the line size of flow meters/flow rates preferred. (Selection Matrix available on request).

c) PLFCS-TB-G – Uncertainty of calibration of Model PLFCS-TB can be further enhanced with integration of Gravimetric calibration mode. One or more precision weighing scales with matching collection vessels – to suit the flow volumes – can be integrated with Model PLFCS-TB. This will enable achieving enhanced uncertainties up to 0.05%.

d) PLFCS-TB-V – Uncertainty of calibration of Model PLFCS-TB can also be enhanced further with integration of Volumetric calibration mode. One or more ‘Standard Volume Provers’ – to suit the flow volumes – can be integrated with Model PLFCS-TB, enabling achieving enhanced uncertainties up to 0.05%.

e) PLFCS-TB-GV – This ultimate alternate model can be a unique combination of CPP (E) + test bed (3 lines) + precision weigh scale with collection vessel or SVP (Standard Volume
Provers) mounted on top. This model will facilitate using the CPP (E) + test bed combo for routine calibrations, but proving/verifying the ‘uncertainty’ of CPP(E) as and when required using the precision weighing scale/SVPs (which offer uncertainty to 0.05%). The Selection Matrix, available on request, will enable selection of model appropriate to meet specific requirements.

All these 5 models of calibration systems/rigs described above are offered with calibration certificates issued by Nagman’s NABL accredited – as per ISO 17025 – Calibration Laboratory.

Key/salient features
Save Water – Water is a scarce commodity in India (and globally as well), and these systems use minimum water unlike conventional flow calibration systems (typically 60 to 150 ltr only – recycled ready for next campaign).

Save Power – Power is an expensive commodity in India and higher kW connections can prove tricky! These systems use only a fraction of power used by conventional flow calibration systems (typically 5 to 25 kW).

Save Space – In many site/lab locations, space proves a constraint. Conventional systems are generally huge and occupy substantial floor space and height. In comparison, these compact systems require much less space and height.

Mobile Skid on wheels/truck – Another major advantage is that these systems can be designed to be mobile, trolley or truck mounted, for moving conveniently closer to sites for calibration routines.

Multi Media Compatible – These systems can be designed to suit liquids other than water, say like EXXOL, for calibration of diesel/fuel meters.

Self-Proving – The ultimate combo model (PLFCS-TB-GV) has inbuilt ‘Standard Volume Provers (SVP)’, mounted on precision weighing scales – which combo enables proving/verifying calibration uncertainty of the system as frequently as desired.

Versatile Test Bed – The separable test bed, with 2/3 independent lines, can accommodate multi type/multiple UUTs (meters under test) for calibration, e.g., this bed can be designed to accommodate (typically):
•    Line 1: 4/5 water meters

•    Line 2: EMF/PD/turbine F/M/PD, and
•    Line 3: Coriolis mass flow meter.

Minimum Upstream (10D)/Downstream (5D) pipe line requirements are met in this test bed (except while using multiple water meters).

Precise Flow-Rate Setting – Control circuit (PLC/software) enables precise setting of flow rates from minimum to maximum .minimum trial runs before calibration run.

Minimum Setting & Calibration Times – Quick calibration campaign is achieved through simple state-of-the-art design of the system, allowing fast setting of flow rates (even up to 5000 LPM) for quick 1/3/5 point calibration. Ideal boon for:
•    Process industries and power stations with limited number of flow meters installed
•    Convenient site calibration of precision flow meters including custody meters, and
•    Site calibration in plants with extended and remote site locations.

Flow Rates & Accuracies/Uncertainties & Line Sizes
•    Flow rates from 0.008 up to 5000 LPM, in 3 models of CPP (E)
•    Uncertainties: 2 Levels, Typical: 0.1% & 0.05% (based on model), and
•    Line sizes: DN 6 up to DN 150 (based on model).

Typical Applications – Practically any type of volumetric or mass flow meter or totaliser can be calibrated, e.g.,

•    Frequency generating flow meters: Turbines, Coriolis, gear/oval gear meters, vortex, etc
•    Analog generating flow meters (0-20/4-20 mA, 0-5/0-10V DC): Magnetic, ultrasonic, venturis, etc., and
•    Visual output flow meters: Variable area meters, totalisers, etc.

Note: The 5 models described above in the article are typical combinations – Nagman can always design and offer a model that will suit customer application/budget! Kindly consult with the company to seek a comprehensively customised system.

About the author: Dr Nagendran Venkatraman is Founder President & Chairman, Nagman Instruments & Electronics Private Ltd, Chennai. Email: [email protected]
The author acknowledges the able support provided by Mr S Karthikeyan, Executive Director (Design & Development), Nagman, in writing of this article.