Model 750 Gas Meter
Installation, Commissioning and Maintenance Manual
Page 6 of 17
© Gyr
17-May-2016
Due to continuous product development the details above are subject to change without notice. Whilst Gyr has taken all reasonable
care in reviewing the information in this document, Gyr makes no representations in respect of, gives no guarantees or undertakings in
relation to, and to the maximum extent permitted by law, excludes all warranties in relation to, the accuracy or completeness of the information
in this document. Prospective users of this information should make their own enquiries as to its accuracy and reliability.
accuracy at Qmax relative to 20% of Qmax). The
ability to set timing is an important feature of the 750
meter. Like a well tuned engine it assures both
smooth operation and reduced wear.
PRESSURE ABSORPTION
Pressure loss is made of two components pneumatic
pressure loss (created by small passage ways and the
movement of gas through the meter) and mechanical
pressure loss a result of moving components.
The mean pressure absorption of the Model 750 is
125 Pascals (Pa) at a flow rate of 6.0 m
3
/hr of air and
125 Pascals (Pa) at a flow rate of 7.5 m
3
/hr of natural
gas (SG 0.62).
ABSORPTION AND OSCILLATION
Pressure
Absorption
is defined as the average
difference between the inlet and outlet pressure when
the meter is run on air over at least one cycle of the
meters operation measured with a British Slope
Gauge.
Pressure Oscillation
is defined as the difference
between the highest and lowest readings of a
pressure gauge placed at the outlet of the meter
measured with a British Slope Gauge.
Although magnahelic and transducers can be used to
determine absorption and oscillation, these devices
must be calibrated to the reference standard, a the
British Slope Gauge as described in AG702.
The acceptance criteria for pressure absorption is no
greater than 125Pa through all flow rates and for
oscillation 75Pa through all flow rates.
METER ACCURACY TREND
Trend is the accuracy at 100% Qmax minus the
accuracy at 20% badge rate shown below. Normally
meters are set with a negative trend rather than a
positive trend due to the falling off in accuracy at low
flow rates (pilot rate).
The 750 high resolution adjustable tangent allows
precision fine tuning of both meter Accuracy and
accuracy trend (accuracy at Qmax relative to 20% of
Qmax). The ability to set timing is an important feature
of the meter. Like a well tuned engine it assures
smooth operation and reduced wear.
This is not available with fixed tangent meters which
use gear trains for pseudo accuracy correction without
provision for timing adjustment.
750's
adjustment
is
self-locking.
It
ensures
maintenance of factory set accuracy during transport
and handling.
ENDURANCE TESTING
Ageing life tests conducted on the Model 750 meter
have provided performance results that demonstrate
the long life and high accuracy for in excess of 15
million cycles.
The Model 750 meter exceeds the endurance testing
requirements
of
the
European
Standard
EN1359:1999, American National Standard ANSI
B109.1, Australian Gas Association AG702, and OMIL
Recommendation
31.
These
standards
and
recommendations are summarised in Table 4 on page
7.
The endurance test results are shown on page 7 show
the equivalent of 27 years in field service, assuming
an annual consumption 1,100 cubic metres per
annum.
The flow rate during the test was continuous at flow
rate of 6 m
3
/hr of natural gas (SG 0.62).
