1 Introduction
Manual TRZ 03· EN08 2018 September, 10th
16
1.4 Method of operation
The method of operation of the mechanical turbine meter is based on the meas-
urement 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 de-
fined flow cross section. In the flow straightener, un¬wanted 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 (Q
min
- Q
max
), 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 an HF pulse
transmitter (HF 1) and gearing which reduces the rotational speed of the turbine
wheel to match the mechanical totalizer. An LF pulse transmitter (slot-type initiator
or reed contact) is located on the totalizer.
Figure 1: Sectional drawing of a turbine meter
shows a sectional drawing of a tur-
bine meter TRZ03. Downstream of the turbine wheel, a cam wheel (reference
wheel) is located on the same shaft. Two HF sensors (proximity switches) gener-
ate a signal if a blade of the turbine wheel (HF 3) or a cam of the reference wheel
(HF 2) passes them. In this way, two pulse sequences are generated which are
out of phase. The generated pulses can be further processed for secondary vol-
ume measurements or flow measurements.
A counter with an integrated encoder (e.g. ENCO 08) processes the pulse se-
quences. The totalizer (Vo) can be transmitted digitally to a flow computer. The
necessary pressure and temperature values can be recorded in the pr connection
(pressure) and via one (or more) temperature sensors in the immersion pocket.