Source: Siemens 2023 | Author: Daniel Henningsen
At Siemens, the magnetically inductive flow meters of type MAG5100W are certified with type approval according to the Measuring Instruments Directive (MID). Within MID, MI-001 refers to water meters and is thus relevant for the MAG5100W.
The critical aspect for design according to MI-001 is the ratio of Q3/Q1. Various values for this ratio are defined according to MI-001 and must be selected during the design process.
This document aims to explain the background of this ratio so that customers gain better insight, ensuring they receive a device that meets their requirements. To understand the background of the Q3 to Q1 ratio, Q3 and Q1 must first be defined.
Q1: The smallest flow rate at which the water meter provides readings that meet the error margin requirements. (DIRECTIVE 2014/32/EU OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL, 2014)
- Minimum flow rate
Q3: The largest flow rate at which the water meter operates satisfactorily under normal use conditions, i.e., under steady or varying flow conditions.
(DIRECTIVE 2014/32/EU OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL, 2014)
- Continuous flow rate
The ratio, also called "R," indicates the flow range for which the measuring device is certified for billing purposes.
This ratio is divided into the following steps, depending on the nominal size:
The higher the value, the larger the measuring range permitted for calibration.
- Q3/Q1=40 means that the minimum flow rate can be 1/40 of the continuous flow rate.
- The larger the ratio, the larger the measuring range, and the more expensive the calibration.
Practical application example:
1. Calculation Ratio
2. Selection of a predefined ratio (theoretically established by MID) multiple options exist
3. Selection of Q3/Q1= 63, as with a ratio of Q3/Q1= 40, only a minimum flow of 2.5 m³/h would be achievable. Ratio of Q3/Q1 greater than 63 is possible. !!always round up!!
By selecting P12, the MAG5100W is certified for billing in the desired flow range.
Alternative: Divide Q3 by the given ratio to determine Q1 and check if it meets the requirements.