Minimum water flow (Qmin)
Minimum water flow for this metre model.
The minimum flow rate is the smallest flow rate at which the counting mechanism can provide measurement with an acceptable error of ±5%. This deviation is higher than the counter error in the standard mode (from Qt to Qn, see below for details), it is considered undesirable, but generally acceptable. But when the flow rate drops below Qmin, the error increases to unacceptable values, and there is no question of acceptable measurement accuracy. So, ideally, it is worth choosing a metre in such a way that its Qmin is not higher than the water consumption at the minimum intensity of consumption. Detailed recommendations for estimating the actual water consumption for different water supply systems can be found in special sources.
Transitional water flow (Qt)
Transitional water consumption for water metre model.
The transitional flow rate is the flow rate at which the maximum measurement error changes — namely, decreases: in the range from Qmin (see above) to Qt it is ±5%, and at the Qt level and above it drops to ±2%. In other words, Qt is the smallest flow rate at which the device gives not just an acceptable, but a minimum error. Thus, the optimal consumption intensity for any metre is in the range between Qt and Qn (see below), and it is this range that is best to focus on when choosing.
Detailed methods and recommendations for estimating water consumption for a particular water supply system can be found in special sources.
Max. water flow (Qmax)
Maximum water flow for water metre .
The maximum flow rate is considered to be the highest flow rate at which the device can operate for a short time (less than 1 hour per day and less than 200 hours per year) without failures, malfunctions and exceeding the maximum allowable error (± 2%). For several reasons, this figure is usually twice the nominal flow rate Qn (see above). When choosing a metre for maximum flow, you need to take into account the peak consumption of the system that it serves — that is, the flow rate when all consumers are turned on maximum at the same time: this rate should not exceed Qmax, otherwise the metre will not be able to cope with its task normally. If the system is constantly operated in the maximum consumption mode, then it is worth choosing not by Qmax, but by Qn.
Sensitivity threshold, less than
Sensitivity threshold for this water metre model.
The sensitivity threshold is the lowest flow rate at which the device begins to respond to the movement of water and record the flow; at a lower speed, the measuring mechanism simply does not distinguish between flow and still water. The lower this indicator, the less likely it is that, at low consumption, water will be consumed without accounting. In household models (see "Type") the sensitivity threshold does not exceed 40 L/h, there are also much lower figures — 10 L/h, or even 5 L/h. In industrial metres designed for large industries, there are values of hundreds of litres per hour.
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