Air velocity measurements are typicaly conducted in closed tube section connected to fan or blower. With change in speed air flow and velocity is varied. However in this arrangement there is wide range of turbulance experienced and it is unadvisable to conduct any measurments as varaitions are significant.
Essential requirements for air velocity measurement are :
Calibration of gas flow could be in volumetric flow or mass flow. Different types of gas flow meters like rotameter, thermal mass flow meter, vortex flow meter and Coriolis gas flow meters. Gas being compressible fluid lot depends on flow pressure and temperature during calibration. At Calitron we calibrate gas flow at low pressure like 7 to 10 psi to ensure near Laminar conditions to have better stability of flow conditions during calibration. This is ensured by having source with enough volume and constant pressure maintained using flow regulator and pressure regulator network
Ranges calibrated are from 0.2 lpm to 100 lpm
Primary method for flow calibration is based on gravimetric method where weight of flow collected in unit time is measured, necessary corrections are applied and flow values are determined. However this procedure needs sophisticated network of pipes, pumping arrangements, timing devices and infrastructure for weighing. Flow meter to be calibrated is connected in network and measurements are carried out. Invariably flow meters are installed at plant are difficult to remove and may stall the operations.
At Calitron we use ultrasonic meter for calibration of flow meter / flow gauging. This device works on ultrasonic principle i.e. there is transmitter and a receiver. Liquids flowing through pipe has certain characteristic values of sound wave transmission which is measured by the ultrasonic meter. This is direct comparison method of device under calibration with calibrated ultrasonic meter. Depending on size of pipe flow sensors are selected. To ensure precision in measurement results it is advised to maintain ultrasonic sensor on straight pipe path with sufficient straight path upstream and downstream.
Measured values include flow velocity and volume flow. Real advantage of this method is on site calibration is feasible without disconnection of flow meters from the system. Flow measurement is possible for any liquid material like water, sewage, oils, petroleum products etc.
