Oval EL4121, Instructions Manual

Page: 11 / 17

E-882-4-E
11
7. CALCULATION FORMULAS
7.1 Implementation of Meter Error Correction (Total flow before correction)
Q1 = a × Ip × (1 + E/100) ×ε
t
where Q
1
: Total flow corrected for meter error ［ l ］
a: Meter factor ［ l/P ］
Ip: Number of input pulses
E: Meter error correction value ［ % ］
The line graph in Fig. 7.1 below shows how meter error curve linearization is achieved. E is approximate-
ly determined by the relationships between input pulse frequency and instrumental error correction value
set at multipoint error points which are programmable along the flowmeter,s instrumental error curve with
front-panel keys, and the frequency pulse information (flowrate) currently arriving from the flowmeter.
7.2 Implementation of Temperature/Pressure Correction (Corrected total flow)
Q
2
= Q
1
× (P/P
0
) × (T
0
/T) ×Χ
where Q
2
: Total flow corrected for temperature and pressure ［ l (normal) ］
Χ : (P
a
＋ P
b
p ＋ P
c
p 2 ) (T
a
＋ T
b
t ＋ T
c
t 2 )
P: p ＋ 0.101325 ［ MPa ・ abs ］
P
0
: p
0
＋ 0.101325 ［ MPa ・ abs ］
T: t ＋ 273.15 ［ K ］
T
0
: t
0
＋ 273.15 ［ K ］
p: Line pressure ［ MPa ］
p
0
: Correction reference pressure ［ MPa ］
t: Line temperature ［℃］
t
0
: Correction reference temperature ［℃ ］
Χ is a correction factor as a quadratic factor of temperature and pressure. Constants Pa thru P
c
and T
a
thru T
c
can be set to any values with keys. Setting P
a
and T
c
to 1 while P
b
, P
c
, T
b
, T
c
to 0 results in 1 at
all times, permitting calculations according to the Boyle-Charles law. By selecting appropriate values for
these constants, you can achieve approximate error correction regarding the deviation of gas compress-
ibility factor, etc.
7.3 Instant Flowrate (Uncorrected)
Q
m
= a × f × (1 + E/100) ×ε
t
× 3600
where Q
m
: Instant flowrate corrected for meter error ［ l/h ］
f: Input pulse frequency ［ Hz ］
7.4 Instant Flowrate (Corrected)
Qmc = Qm × (P/P
0
) × (T
0
/T) ×Χ
where Q
mc
: Instant flowrate corrected for temperature and pressure ［ l/h (normal) ］
＋
0
−
F
1
F
2
F
3
E
1
E
2
E
3
E
4
F
4
F
8
E
8
E
F
9
｝
9
Fig. 7.1
M
et
er
e
rro
r
Flowrate
(frequency)
F
1
thru F
9
Frequency (Hz)
E
1
thru E
9
Meter error correction value (%) Programmable with keys
ε
t
: Meter,s correction factor relative to temperature
variation
ε
t
= 1 + 3 α (t − 20)
t = Operating temperature ［℃ ］
3 α = 4.8 × 10 − 5 (stainless steel)