ISO 3455:2021 pdf download.The title is Hydrometry — Calibration of current-meters in straight open tanks.
ISO 3455 specifies a calibration method for mechanical type, electromagnetic type and acoustic type hydrometric current-meters used for point velocity measurement of flowing water.
The method requires towing the instrument through still water in a straight open tank. It includes measuring apparatus, the calibration procedure, the method of presenting the results and the uncertainties associated with the method.
5.3.3 Time measurement
The time of travel of the cart is normally measured by an electronic counter with an in-built accuratetime reference,for example a quartz crystal.A period can thus be read to 1 ms or better.This equipmentshould be checked periodically against a reference device traceable to a national time standard.
5.3.4 Current-meter velocity measurement
The cart shall be provided with a suitable recording device for the measurement of current-metersignals.
In the case of rotating-element current-meters,the sensor of the current-meter shall generate a clearand positive signal corresponding to the rotor revolutions.Normally,as per the design of the system,the signals are gencrated once per revolution,twice per revolution,or in some cases,once for fiverevolutions or even once for 10 revolutions.The signals received from the current-meter(s)may becounted using the counting device of the current-meter.In measuring the number of current-meterrevolutions in a given time,it is important to measure between identical points on the current-metersignal.It shall be ensured that none of the signals are missed.