VEGA VEGABAR 87 4 … 20 mA_HART - Operating Instructions - Manual (Page 56)

56
9 Diagnosis, asset management and service
VEGABAR 87 • 4 … 20 mA/HART
45044-EN-131010
•
F
T
: Thermal change of zero signal and output span
•
F
Kl
: Deviation
•
F
a
: Thermal change of the current output
You can find the specifications in chapter "Technical data".
Level measurement 1500 mmWs
Product temperature up to 40 °C
VEGABAR 87 with measuring range 0.2 bar
Deviation < 0.1 %
Calculation ΔT: ΔT = 40 °C - 20 °C = 20 K
Calculation of the set Turn Down:
TD = 200 mbar/147 mbar, TD = 1.4
1. step: Calculation of the basic accuracy
F
perf
= √((F
T
) 2 + (F
Kl
) 2 )
F
T
= (0.15 %) x (0.5 + 0.5 x TD)
F
Kl
= 0.1 %
F
perf
= √((0.15 %) x (0.5 + 0.5 x TD) 2 + (0.1 %) 2 )
F
perf
= 0.21 %
Step 2: Calculation of the total deviation
F
total
= F
perf
+ F
stab
F
stab
= (0.05 % x TD)
F
stab
= (0.05 % x 1.4)
F
stab
= 0.07 %
F
total
= 0.21 % + 0.07 % = 0.28 %
1. step: Calculation of the basic accuracy
F
perf
= √((F
T
) 2 + (F
Kl
) 2 + (F
a
) 2 )
F
T
= (0.15 %) x (0.5 + 0.5 x TD)
F
Kl
= 0.1 %
F
a
= 0.15 %
F
perf
= √((0.15 %) x (0.5 + 0.5 x TD) 2 + (0.1 %) 2 + (0.15 %) 2 )
F
perf
= 0.25 %
Step 2: Calculation of the total deviation
F
total
= F
perf
+ F
stab
F
stab
= (0.05 % x TD)
F
stab
= (0.05 % x 1.4)
F
stab
= 0.07 %
F
total
= 0.25 % + 0.07 % = 0.32 %
9.6 Exchange process assembly with version
IP 68 (25 bar)
With version IP 68 (25 bar), the user can exchange the process as-
sembly on site. Connection cable and external housing can be kept.
Practical example
Calculation - Digital out-
put signal
Calculation - Analogue
output signal