VEGA VEGABAR 83 Profibus PA - Operating Instructions - Manual (Page 56)

56
9 Diagnosis, asset management and service
VEGABAR 83 • Profibus PA
45037-EN-131107
9.5 Calculation of total deviation (according to
DIN 16086)
The total deviation of a pressure transmitter indicates the maximum
measurement error to be expected in practice. It is also called maxi-
mum practical deviation or operational error.
According to DIN 16086, the total deviation F
total
is the sum of the
basic accuracy F
perf
and the long-term stability F
stab
:
F
total
= F
perf
+ F
stab
The basic accuracy F
perf
is composed of the deviation F
Kl
and the
thermal change of zero signal and output span F
T
:
F
perf
= √((F
T
) 2 + (F
Kl
) 2 )
This applies to the digital signal output via HART, Profibus PA or
Foundation Fieldbus. With a 4 … 20 mA output, there is also the
thermal change of the current output F
a
:
F
perf
= √((F
T
) 2 + (F
Kl
) 2 + (F
a
) 2 )
To provide a better overview, the formula symbols are listed together
below:
•
F
total
: Total deviation
•
F
perf
: Basic accuracy
•
F
stab
: Long-term drift
•
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".
Pressure measurement in the pipeline 8 bar (800 KPa)
Product temperature up to 50 °C
VEGABAR 83 with measuring range 10 bar, deviation < 0.075 %
Calculation of the turn down: TD = 10 bar/8 bar, TD = 1.25
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
= 0.075 %
F
perf
= √((0.15 %) x (0.5 + 0.5 x TD) 2 + (0.075 %) 2 )
F
perf
= 0.19 %
Step 2: Calculation of the total deviation
F
total
= F
perf
+ F
stab
F
stab
= (0.05 % x TD)
F
stab
= (0.05 % x 1.25)
F
stab
= 0.06 %
F
total
= 0.19 % + 0.063 % = 0.25 %
1. step: Calculation of the basic accuracy
F
perf
= √((F
T
) 2 + (F
Kl
) 2 + (F
a
) 2 )
Meaning of the total
deviation
Practical example
Calculation - Digital out-
put signal
Calculation - Analogue
output signal