VEGA VEGABAR 87 Modbus and Levelmaster protocol - Operating Instructions - Manual (Page 48)

48
8 Diagnosis, asset management and service
VEGABAR 87 • Modbus and Levelmaster protocol
46297-EN-131107
8.5 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 )
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
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 %
Meaning of the total
deviation
Practical example
Calculation