Glossary

Water meters

Q3 – permanent flow rate

The flow rate at which a water meter may be operated continuously. For the H2O from 2.5 m³/h (DN15) to 4000 m³/h (DN600).

Q4 – overload flow rate

Highest flow rate permitted for short periods. For the H2O, 1.25 times Q3.

Q1 – minimum flow rate

Lowest flow rate at which the meter measures within the maximum permissible errors.

Dynamic range R

Ratio Q3/Q1, for heat meters qp/qi. R400 means the meter measures accurately down to one four-hundredth of the permanent flow rate.

Temperature class

Upper limit of the water temperature, for example T50 for 50 °C. The H2O is available with T30, T50, T70 and T90.

Reverse flow

Water flowing against the direction of the arrow. The H2O records forward and reverse volume separately.

Straight inlet and outlet sections

Straight pipe upstream and downstream of a meter that allows the flow profile to settle. The H2O and DELTA III need none from DN15 to DN40.

WRAS

UK approval for products in contact with drinking water. The H2O is WRAS-approved.

Heat meters and temperature

Heat meter

Measuring instrument for thermal energy, consisting of a flow sensor, a temperature sensor pair and a calculator.

Cooling meter

Measures cooling energy; the return is warmer than the flow. The DELTA III counts heating and cooling in separate registers.

BTU meter

Term for heat and cooling meters common in the Middle East and North America. BTU stands for British Thermal Unit.

Flow

Pipe from the heating or cooling source to the consumer.

Return

Pipe from the consumer back to the source.

Temperature difference Δθ

Difference between flow and return temperature in kelvin. The smaller the Δθ, the more accurate the sensors need to be.

Kelvin (K)

Unit for temperature differences. 1 K equals a difference of 1 °C.

Heat coefficient k

Factor accounting for the density and specific heat capacity of water, which depend on temperature. Defined in EN 1434.

Calculator

The heat meter’s electronics, which calculate the energy from volume and temperatures, display it and store it.

Pt500 / Pt1000

Platinum resistance sensors with 500 Ω or 1000 Ω at 0 °C. Pt1000 is less sensitive to the resistance of the connecting cable.

Temperature sensor pair

The two matched temperature sensors of a heat meter.

Split type

Calculator mounted separately from the flow sensor, connected by a cable.

qp – nominal flow rate

Continuous flow rate of a heat meter. For the DELTA III from 1.5 m³/h (DN15) to 6000 m³/h (DN1000).

qi / qs

Lowest and highest permitted flow rate of a heat meter. For the DELTA III, qs = 2 × qp.

Ultrasound

Ultrasonic transducer

Component that converts electrical pulses into sound and vice versa. Two transducers alternately send and receive.

Transit time method

Measuring principle that compares the transit time of a sound pulse with and against the flow. The difference is proportional to the flow velocity.

Reflector

Mirror in the measuring tube that guides the sound along a defined path. Metallic and self-cleaning in the DELTA III.

Measuring channel

One sound path through the pipe. The DELTA III measures with 2 channels from DN50 and 4 from DN350.

Air in pipe

Air bubbles disturb sound propagation. Ultrasonic meters detect this and report an error.

Flushing

Flushing new pipework before the meter is fitted, to remove dirt and installation debris. Until then, a spool piece is fitted in place of the meter.

Standards and approvals

MID

European Measuring Instruments Directive 2014/32/EU. A prerequisite for meters used for billing.

Module B and module D

Conformity assessment procedures under the MID: B is the type examination, D the quality assurance of production.

EN 1434

European standard for heat meters.

EN 14154 / ISO 4064

Standards for water meters.

OIML R 49

International recommendation for water meters, the basis of many national regulations.

IP68 / IP65

Degrees of protection against dust and water. IP68: continuous immersion.

Communication

M-Bus

Meter-Bus to EN 13757: two-wire bus on which one master reads many meters.

Secondary address

Unique M-Bus address assigned to a meter at the factory.

Wireless M-Bus

Radio version of M-Bus; for the H2O in S1, T1 and OMS modes.

RS-485

Electrical interface for differential data transmission over a twisted pair.

Modbus RTU

Master-slave protocol that runs over RS-485.

LoRa

Radio network protocol for low-power devices; in Europe it uses the 868 MHz band.

OTAA

Over-the-air activation: a LoRa device joins the network with newly derived session keys.

NB-IoT

Mobile network standard for small amounts of data.

Optical interface D0

Infrared interface on the front of the meter for on-site configuration and reading.