A Cost Effective Flow Calibration Skid
Dr V Nagendran elaborates upon a mobile flow calibration skid as an effective solution for companies with limited resources.
Nagman Instruments and Electronic Pvt. Ltd
Calibration of Flow Meter
Mobile Flow Calibration Skid
Medium sized process industries with fairly limited number of flow meters installed are by and large handicapped in getting these flow meters calibrated regularly – at least at one year frequency – as per ISO stipulations, ensuring their continued performance per original specifications.
These industries may not be able to afford to remove the flow meters and forward these to the nearest Flow Calibration Laboratory – ISO 17025 accredited or with calibration accuracies traceable to international standards – duly considering the “extended turndown” periods (to perform calibration and return) of these laboratories – generally around a couple of weeks (including the transit times) – which will invariably affect their busy production schedules/commitments.
Nor can they afford to source and install a regular ‘flow calibration system’ – high costs of ownership, space constraints, electrical power and skilled man power requirements, etc., weigh heavily, affecting the economy of calibration.
A reasonable compromise – a cost effective solution under such a situation can be a “(Mobile) Flow Calibration Skid” – with lower cost of ownership, limited space/electrical power/operator skill requirements – facilitating, ‘at will’ calibration facility at their site!
Typical system will consist of the following minimum modules:
An integral water reservoir – 1500 ltr (maximum 2000 ltr – considering mobility)
One or two pumps with variable frequency drives to control volume deliveries
One or two master/reference flow meters (for comparison method of calibration), and/or
One or two collection tanks, mounted on precision weighing scales* and one or two open type diverter systems (if gravimetric calibration is to be performed)
Test bed – with flow straighteners, control valves, pipelines, spacers, adapters, etc
Clamping system for mounting flow meters
Temperature and pressure measuring devices, and
Density meter (off-line).
*In Gravimetric Mode of calibration, it must be reckoned that calibration accuracies of weighing scales tend to drift during transportation, and hence recalibration at site – once stationed – is mandatory. Mobility is thus restricted.
Such a typical skid can handle flow rates from 5 LPM up to about 2500 LPM and flow meter sizes from DN 6 (¼”) up to DN 100 (4”). Most types of process flow meters – like turbine, vortex, ultrasonic, etc., – with accuracies up to 0. 5% can be calibrated with this skid at site.
While Comparison Method – cost effective calibration is performed with reference to ‘pre-calibrated ‘Reference/master flow meters of 0.2% accuracy** (typical CMCs around 0.25%) – Gravimetric Method affords calibration with enhanced ‘Calibration Measurement Capabilities’, tending close to 0.1%. In this mode ‘Collection Tanks’ mounted on precision weigh scales collect the water during a campaign. Volume of water flown during a campaign is computed by dividing the mass by density***.
**Accuracies in comparison method calibration can be enhanced using Coriolis mass flow meters with accuracies to 0.1 / 0.05% (which can also be used for online ‘density measurement’).
Flow Rate Setting is through VFDs (Coarse) and throttle/control valves (Fine).
Turbulence in lines – particularly within the limited space/lengths – is adequately minimised using ‘flow straightening devices’ in line. Operation can be manual or semi-automatic. Integral water reservoir – below the test bed – enables optimal use of water resources on recycling mode! Pumps can be mounted on ‘cushy foot’ mounts to minimise vibration effects.
Open type ‘diverters’ – in case of gravimetric calibration – which divert water flow to the collection tanks or on to the return drain lines, can be designed with optimal ‘transit times’ to improve the calibration & measurement capabilities (CMCs). Operations can be ‘Flying Start & Stop’ method.
Temperature measurements ‘on line’ enables corrections*** due to changes in density of water, due to temperature variations. Pressure measurements ‘on line’ enables alert on pressure drops due to partially blocked meters under test. Clamping system enables quick mounting of meters under test. A variety of adapters/spacers enable meters under test with varied line sizes to be mounted and calibrated.
The entire system modules can be accommodated/mounted in a sturdy steel frame, with lifting lugs – enabling transport this skid to customer locations/sites.
Typical dimensions shall be approximately 4000 (L) x 2000 (B) x 2000 (H) mm (Comparison Method).
Typical power requirement will be 25 kW.
It is used in Thermal, Mechanical, Electro-Technical & Flow industry.
Nagman Instruments and Electronic Pvt. Ltd
Dr V Nagendran
He is the Founder Chairman, Nagman Instruments, with 50+ years experience as hard core instrumentation professional – technopreneuer. As a creative technocrat he pioneered the ‘Make in India’ concept for over a decade, before developing with in-house expertise scores of innovative and unique import substitution products and systems in key process parameters of temperature, pressure, electrical, flow and level. The ‘Made in India’ NAGMAN brand – 45 years young but strong – duly supported by ISO/IEC 17025 : 2005 Accredited Calibration Laboratory – offers world class calibrators/systems/software & calibration services.