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HPLC digital liquid flow meters are widely used for IQ OQ PQ (qualification and validation programs) and troubleshooting in the research lab and in industry. As with all precision instruments, they must be calibrated prior to being put into initial operation and periodically recalibrated to ensure their accuracy is maintained, as a key component of quality control.
The digital flow meters, such as Tovatech's FlowCal 5000 model, are shipped factory-calibrated along with an accompanying calibration certificate for a flow rate of 1 .0 ml/min plus additional flow rates requested by the customer. The calibration certificate certifies that the displayed flow rate is within ±1% of the actual flow rate at each calibration point.
Initial calibration steps
Calibration points recorded on the certificate are not based on single measurements. Instead they result from an extensive process aimed at achieving statistically accurate data by taking, for example. 30+ readings at 0.5ml/min. 40+ readings at I.Oml/min and -100 readings at 5.0ml/min. Data are captured and averaged via an RS 232 interface to a PC. The certificate shows the average of these readings at each flow rate. The percent error and percent standard deviation from the actual flow rates are also calculated from these averages and shown on the certificate.
The actual flow rate is determined gravi metri cal Iy. not with a reference flow meter, but by collecting a mass of water passing through the flow meter over a recorded period of time. The mass of water is converted to a volume of water by correcting for density (based on the water temperature). The actual flow rate can then be ascertained from the volume over time measurements. This is compared to the displayed readings on the flow meter. The meter's firmware is adjusted to allow the displayed rate to match the actual flow. Calibration equipment, the balance and counter timer are calibrated annually by an accredited certification lab. This provides traceability of measurement to recognized national standards.
Recalibration processes
In accordance with GLP and to comply with other regulations, digital liquid flow meters should be recalibrated annually. Recalibration procedures follow the same format used for initial calibration as described above.
The flow meter is first flushed with water. Then "as found" (or "before") readings are taken at...