First of all, our HPLC flow meters 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.

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 1.0ml/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 gravimetrically, not with a reference flowmeter, 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 flowmeter. The firmware of the flow meter 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 flowmeters 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 1.0ml/min to measure the accuracy of the flow meter in the state in which it was received. Customers may request that calibration certificates show “before” data at all the calibration points rather than exclusively at 1.0 ml/min. The flow tube is cleaned, sensors are checked, any repairs undertaken, and necessary adjustments are made to bring the flow meter into specification. The flow meter is then calibrated to all the customer’s required flow rates. “After” data are recorded on the calibration certificate to confirm that the returned flowmeter is performing according to specification.

Tovatech scientists will be happy to answer other questions you may have regarding the FlowCal 5000 digital liquid flowmeter.

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What procedures are in your company operations manual to guide recalibration scheduling for a digital liquid flow meter?

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