Nominal diameter is not the measurement range
Specifying DN20, DN25 or DN50 alone does not define a meter’s low-flow capability. DN concerns the pipe connection; the ratio R = Q3/Q1 describes the declared measurement range under OIML R 49. Two meters with the same nominal diameter may perform differently at low flow. The approved installation orientation, temperature class and operating conditions must also be compared.
Understanding Q1, Q2, Q3 and Q4
Q1 is the minimum flow rate at which the specified metrological error limits apply. Q2 separates the lower and upper flow-rate zones. Q3 is the permanent flow rate under normal operating conditions. Q4 is a short-duration overload flow, not a recommended continuous operating point. A higher R ratio extends the declared range; it does not automatically change the accuracy class.
Worked example: Q3 = 4 m³/h and R160
The following numbers are an illustrative engineering example, not specifications for any ATLAS model. Q1 = 4/160 = 0.025 m³/h, or 25 L/h. Under the ratios in OIML R 49-1:2024, Q2 = 1.6 × Q1 = 40 L/h, and Q4 = 1.25 × Q3 = 5 m³/h. At the same Q3, R400 would imply Q1 = 10 L/h. Always verify that the actual product is approved for the advertised Q3/R pairing and accuracy class.
Ten points to check in a technical specification
State whether the meter serves potable/clean water, its temperature range and whether it is used for billing.
Specify DN, Q3 and R (Q3/Q1) as separate requirements.
Review the approved Q1–Q4 range, accuracy class and installation orientations.
Verify the applicable legal metrology conformity, such as MID MI-001, for the exact device variant.
Check permissible pressure, temperature class, pressure loss and material suitability.
Define the required ingress-protection test: IP65 and IP67 are not interchangeable claims.
Evaluate battery autonomy under a stated reporting interval and duty cycle.
Separately specify required LoRaWAN, NB-IoT, M-Bus or pulse data interfaces and data fields.
Require prepaid functions, valve actuation or display options only where the exact model supports them.
Define sample acceptance tests for flow, serial identification, sealing, communications and documentation.
Avoid common tender comparisons
A meter registering some movement below Q1 is not evidence of approved accuracy there. Similarly, an “ultrasonic” meter is not necessarily a remotely connected or prepaid meter. Separate metrological conformity, digital connectivity and commercial requirements into distinct specification sections to avoid misleading comparisons.
Information needed for an engineered quotation
Supply the application, DN, minimum/typical/peak flow, water temperature, operating pressure, pipe arrangement, communication architecture and required compliance records. The ATLAS ultrasonic water-meter product range can then be reviewed against documented, model-specific data.
Next step: Review the ATLAS ultrasonic water-meter family and request model-specific documentation against your tender’s flow table.
Kaynak başlıkları / References: OIML 2024, MID 2014/32/EU