77
10 Supplement
WIKA Operating Instructions - Differential pressure transmitter DPT-20
Advanced Function Blocks
Discret Input (DI)
Yes
PID Control
Yes
Output Splitter (OS)
Yes
Signal Characterizer (SC)
Yes
Integrator
Yes
Input Selector (IS)
Yes
Arithmetic (AR)
Yes
Diagnostics
Standard
Yes
Advanced
Yes
Performance
No
Function Blocks Instantiable
No
General Information
LAS (Link Active Scheduler)
Yes
Master Capable
Yes
Number of VCRs (Virtual Communication Re
-
lationships)
47
10.3 Calculation of the total deviation
The total deviation of a pressure transmitter indicates the maximum measurement error to be ex
-
pected in practice. It is also called maximum practical deviation or operational error.
According to DIN 16086, the total deviation F
total
is the sum of the basic deviation F
perf
and the long-
term stability F
stab
:
F
total
= F
perf
+ F
stab
The basic deviation F
perf
in turn consists of the thermal change of the zero signal and the output
span F
T
(temperature error) as well as the deviation F
Kl
:
F
perf
= √((F
T
)
2
+ (F
Kl
)
2
)
The thermal change of the zero signal and output span F
T
is specified in chapter "
Technical data
".
This applies initially to the digital signal output through HART, Profibus PA, Foundation Fieldbus or
Modbus.
With 4 … 20 mA output, the thermal change of the current output F
a
must be added:
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 deviation
•
F
stab
: Long-term stability
•
F
T
: Thermal change of zero signal and output span (temperature error)
•
F
Kl
: Deviation
•
F
a
: Thermal change of the current output
•
FMZ: Additional factor measuring cell version
•
FTD: Additional factor Turn down
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