1 Introduction
Manual TRZ 03· EN08 2018 September, 10th
20
density. The lower flow limit shifts in the direction of smaller loads (see also table
in
chapte r6.3
Q
min
depending on the operating pressure in natural gas
). Use the formula be-
low as approximate equation:
)
/
(
2
,
1
3
min
h
m
Q
Q
md
•
The density
can be determined with the following approximate formula:
)
/
(
)
1
(
3
m
kg
p
n
m
•
+
The influence of the temperature is not taken into account in this formula.
With:
Q
md
: Minimum flow rate at flowing conditions
Q
min
: Minimum flow rate of the gas meter
p
m
:
Operating pressure in bar
:
Density in kg/m³ (density of air at 20° C and 1,01325 bar
1,2 kg/m³)
n
:
Standard density of the gas (standard density of natural gas
0,8 kg/m3)
1.9 Accuracy of measurement
The following error limits apply within the permissible measuring range:
Measuring range:
Q
min
to 0,2 Q
max
0,2 Q
max
to Q
max
Calibration limit
1)
2 %
1 %
TRZ 03
1 %
0,5 %
TRZ 03-K
2 %
(DN 50, DN 80:
3 %)
1 %
(DN 50:
1,5 %)
1)
maximum error due to the German Metering and Calibration Rules
It will be checked whether these limits are observed. They also apply to the high-
pressure range.