Technical specifications of water meters

Qmax water meter - maximum flow rate - the highest flow rate at which the water meter should operate for a short time (less than 1 hour per day and less than 200 hours per year) without exceeding its maximum permissible error.

Qn water meter - nominal flow rate - the highest water flow rate at which the water meter should operate for a long time without exceeding its maximum permissible error.

Qt water meter - transitional flow rate - the water flow rate at which the maximum permissible error of the flow meter changes.

Qmin water meter - minimum flow rate - the smallest water flow rate at which the measurement error of the flow meter does not exceed the maximum permissible error.

DN water meter - nominal diameter - the diameter of the opening in the connecting flanges. The value of DN is used to standardize the sizes of pipeline fittings. The actual diameter of the opening may differ slightly in either direction.

PN water meter - nominal pressure - the internal pressure, expressed in bars, which corresponds to the maximum allowable working pressure of water.

Metrological characteristics

Technical specifications of water meters

Metrological accuracy classes according to the ISO 4064-1 standard

1 - Actual error curve of the water meter
2 - Maximum permissible error of the meter at flow rates from Qt to Qmax
3 - Maximum permissible error of the meter at flow rates from Qmin to Qt
4 - Range of low water flow
5 - Working range of water flow

Maximum permissible errors in the range:

from Qmin to Qt - maximum permissible error is +/-5%
from Qt to Qmax - maximum permissible error is +/-2%

Metrological classes of water meters regulated by ISO 4064

Water meter classes	Qn < 15 m³/h	Qn >/= 15 m³/h
Class A Value of Qmin Value of Qt	Class A 0.04 Qn 0.10 Qn	Class A 0.08 Qn 0.30 Qn
Class B Value of Qmin Value of Qt	Class B 0.02 Qn 0.08 Qn	Class B 0.03 Qn 0.20 Qn
Class C Value of Qmin Value of Qt	Class C 0,01 Qn 0,015 Qn	Class C 0,006 Qn 0,015 Qn