Our Article in Automation Magazine – April 2017

ENELSAN'S MAJOR INVESTMENT IN FLOWMETER CALIBRATION STATION It established the calibration station, which is a prerequisite for any flowmeter production, and commissioned it with the first production as a result of two years of R&D studies. The first TÜRKAK-approved calibration station covered the maximum flow rate of 700 m3/h. It has reached a capacity of 10,000 m3/hour with the new calibration station, which it designed and completed its investment with the support of TUBITAK last year. Especially, in the calibration of large-diameter flow meters, one of two different approaches is generally chosen in the world. One of the solutions is to fill the liquid to be used in calibration (water as standard for electromagnetic flowmeter) into a tower and compare the intermediate volumes determined by level switches placed at fixed intervals while flowing from this tower by gravity with the volume measured by the calibrated device. It is expected that the measurement will be done at two, rarely three points of the nominal flow of the flowmeter, which is calibrated at once during the calibration processes with these towers, that are produced with a height of 30-40 meters and a diameter of 3-4 meters. International rules stipulate that a measurement period should last a minimum of 60 seconds. In other words, with a volume of 500 m3 (meaning a tower with a diameter of about 4 meters and a height of 40 meters), it is possible to reach a maximum flow rate of 8,000 m3/hour, if we also consider the take-off stop time losses. Such calibration stations optimize the calibration times to lower time intervals and evaluate the statistical data they have obtained as a result of trial and error methods, completing the entire calibration routine in a single discharge and getting the printouts. Enelsan's first calibration station with TÜRKAK accreditation is based on the rule of weight, which is also used by UME (National Metrology Institute) within TÜBİTAK. In this system, after a reference flow meter is calibrated with a traceable tank, it evolves into the process of comparing the flowmeters to be calibrated with the reference flowmeter. One of the obvious difficulties of such a method is the very precise determination of the start and end times at which the water flow is diverted to the tank. A second requirement can be defined as the continuous monitoring of more than one reference flowmeter of different diameters with the tank weight for different flow rates. Accredited calibration stations using this method generally perform mass-volume correction by entering the temperature/density table of the water. As a result of measuring the actual density of the water passing through the line at the Enelsan calibration station and transferring it to the calculation programs, the measurement and thus the calibration reliability is increased. Among the tower and reference flowmeter methods, the most valid argument in favor of calibrating with a reference flowmeter is the possibility of performing the calibration separately and repeatedly at many desired flow rates. While it is possible to calculate the flow value from the time elapsed between two levels in a tower (which can never be an expression of a constant value since the water column will change between the start and the end), it is possible to continuously adjust the desired flow values in the reference flowmeter method and set out the calibration after the flow stabilized has gaining importance as a high-level application. Another very vital advantage is that the calibration is performed for very long periods of time to reach large volumes, increasing the resolution. For example, with flowmeters programmed to output 1 pulse/liter, a resolution of 10 times higher, such as 1/2000 for 2000 liters and 1/20.000 for 20,000 liters in total, will be achieved. Since the calibration with reference flowmeters is done with the continuous circulation of water, it is an important advantage that there is no pre-preparation requirement such as filling the tower with water to start a calibration function. There will be no loss of time, especially in transactions that are required to be repeated. Enelsan's new calibration station, which has the ability to calibrate up to 10,000 m3/hour, is based on the principle of using multiple flowmeters with the largest diameter calibrated as a reference flowmeter in an accredited calibration station in parallel and comparing their total flow with a larger diameter flowmeter that is desired to be calibrated. Description of the system A pool of 400 m3 volume, 10 DN 400 reference flow meters mounted on one side of this pool to draw water from the floor, a DN 2000 collector fed by them, and after the collector, reduction and straight pipelines with the desired diameter (DN 600-DN 2000) flowmeter It can be summarized as a mechanism that provides a return to the pool, which has a camel neck at the end, to which it can be connected. Each of the pumps has a power of 36 kW and each is equipped with motor drives fed by a separate inverter. It is controlled by a powerful PLC that balances both revolutions and load distributions, and the calibration process is completed by comparing the sum of the pulse outputs of the reference flowmeters with the pulse output of the flowmeter under test with the same PLC and appropriate software. Reference flowmeters are calibrated with an accuracy of +/- 0.1% at nominal flow rates, and periodic inspections are made. It will be seen in a simple equation that even in the worst case where 10 pumps work together and all with + error, the error in their total will still be limited to +0.1%. Probability points out that some of them will work with + some - errors and the total error will be less than 0.1%. With its high frequency input modules and powerful software, the calibration station is capable of easily performing comparison and reporting operations without putting too much burden on the operator. The said calibration station, which was built with an investment of approximately 2 million Turkish Liras, has increased the flowmeter manufacturing capability of Enelsan Industrial Electronics Industry A.Ş. up to DN 2000 (80'') and aims to meet the calibration requirement of this capacity in Turkey and the nearby region.