3. Accuracy after temperature and pressure correction
As an example, we will calculate the accuracy after temperature and pressure cor-
rection at 100 m
3
/h and 150 m
3
/h (normal), using the following formula:
Accuracy after
correction
(%RD) = (
volumetric flow
rate accuracy
(%RD)
2
+
temperature
accuracy
(%RD)
2
+
pressure
accuracy
(%RD)
2
)
Temperature and pressure sensor accuracy is as follows:
Temperature measurement accuracy: ±2 % RD (absolute temperature base)
Pressure accuracy (%RD) = (upper limit of operating pressure range (MPa) × pres-
sure measurement accuracy (%FS)/100)/(fluid pres-
sure (MPa) + 0.1013 (MPa))
In this case, the pressure measurement accuracy is 1 %FS in the 0-1.0 MPa range of
the
MVF0800
(operating pressure range 0-1.0 MPa).
In order to calculate the volumetric flow rate accuracy, the Reynolds number is first
calculated from the mass flow rate (m
3
/h, normal).
The steps of the calculation are: mass flow rate
→
volumetric flow rate
→
velocity
→
the Reynolds number.
Mass flow rate
→
volumetric flow rate calculation
Qactual (m
3
/h) = 100 × ((273+23)/(273+0) × (101.3/(101.3 + 700)) = 13.7
Volumetric flow rate
→
Velocity calculation
Velocity V(m/s) = Qactual(m
3
/h)/S/3600 = 13.7/((78 × 10
–3
)
2
× π/4)/3600 = 0.8
S: flow path cross-section of
MVF080
(m
2
) = (78 × 10
–3
)
2
× π /4
Velocity
→
Re calculation
Re = (V × D)/ ν = 0.8 × 78 × 10
–3
/ 1.883 × 10
–6
= 33139
V: velocity (m/s) = 0.8
D: internal diameter of the
MVF
body (m); for
MVF080
, D = 78 mm
ν: kinetic viscosity of fluid (m
2
/s)
For dry air, 23 °C and 700 kPa, ν = 1.883 × 10
–6
m
2
/s
Volumetric flow rate accuracy is checked by the Reynolds number.
With Re = 33139 (flow rate = 0.8 m/s), since the velocity is 0.5 m/s or more and the
Reynolds number is in the 10000-35000 range, the volumetric flow rate accuracy is
±4 % RD.
●
Specifying volumetric flow rate accuracy (page 22)
Volumetric flow rate accuracy = 4 % RD
Temperature accuracy = 2 % RD
Pressure accuracy = 1 (MPa) × 1 (%FS)/100/(fluid pressure (MPa) + 0.1013 (MPa))
= 0.01/(0.7+0.1013) = 1.2 % RD
In this case, the pressure measurement accuracy is 1 %FS in the 0-1.0 MPa range of
the
MVF0800
(operating pressure range 0-1.0 MPa).
Based on these conditions,
The accuracy after temperature correction = (4 %)
2
+ (2 %)
2
+ (1.2 %)
2
= 4.6 %RD
21
Chapter 5. SPECIFICATIONS
