Operation
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Manual TRZ 04 · EN04 · February, 1st 2017
43
3 Operation
3.1 Influences on the error of measurement due to
operation
3.1.1 Intermittent
operation
Warning
Rapid changes of the gas flow should be avoided, since the turbine wheel
can follow these changes only with a certain delay due to its inertia. In this
way, errors of measurement occur, in particular, if the gas flow is shut off.
Since in this case the turbine wheel slows down after the flow has stopped, a
gas volume is measured which is always higher than that which has actually
flowed through the gas meter.
3.1.2
Influence of pulsations
The gas flow must be free of shocks or pulsations. A gas metering station can be affected
by flow pulsations, however, if the following equipment has been installed upstream or
downstream in the system:
reciprocating piston compressors,
rotary displacement meters,
gas pressure regulators lacking steadiness of operation,
pipes where no gas flows (siphons).
Volume flow pulsation
is the decisive quantity for evaluating the performance of gas
meters under the influence of pulsations. Volume flow pulsation is physically always
associated wit
h
pressure variations
.
The following relation is established in a first
approximation:
K
Q
DN
p
Q
rel
rel
2
With:
Q
^
rel
:
is the relative volume flow pulsation (peak-to-peak)
Q
¯:
is the mean volumetric flow
p^
rel
:
is the relative pressure pulsation (peak-to-peak)
DN: is the nominal diameter of the gas meter
K:
is a constant depending on standard density, velocity of sound, compressibility,
pressure at base conditions, temperature, and station-specific parameters.
