Installation and Commissioning
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Manual TRZ 04 · EN04 · February, 1st 2017
16
1.4 Method of operation
The method of operation of the mechanical turbine meter is based on the measurement of
the gas velocity. The velocity of the gas flowing through the gas meter is increased in the
flow straightener and the gas strikes the turbine wheel in a defined flow cross section. In
the flow straightener, unwanted vortices, turbulences and asymmetries are removed or
reduced. The turbine wheel is mounted axially, while the blades of the turbine wheel are
arranged at a certain angle to the gas flow. Within the measuring range (Qmin - Qmax),
the rotational speed of the turbine wheel is almost proportional to the mean gas velocity
and, therefore, to the rate of flow. The number of rotations is a measure of the volume that
has flowed through. The rotary movement of the turbine wheel is transmitted by a
magnetic coupling to the unpressurized meter head. Downstream of the coupling, there is
a gearing which reduces the rotational speed of the turbine wheel to match the mechanical
totalizer. Two LF pulse transmitters (reed contacts) and a tamper contact are located on
the totalizer.
Figure 1: Sectional drawing of a turbine meter.
Downstream of the turbine wheel, a cam wheel (reference wheel) is located on the same
shaft. Two HF sensors (proximity switches) generate a signal if a blade of the turbine
wheel (HF 3-D) or a cam of the reference wheel (HF 2-D) passes them. In this way, two
pulse sequences are generated which are out of phase. The generated pulses can be
further processed for secondary volume measurements or flow measurements.
Flow
straightener
Meter head with
mechanical index,
Encoder and LF
pulse transmitters
Turbine
wheel
Reference
wheel
HF pulse
transmitters
Introduction
