Siemens SITRANS LR 300, Instruction Manual, Page: 124 / 140

Page 122 SITRANS LR 300 – INSTRUCTION MANUAL 7ML19985CL02
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Appendix VII
Function Blocks – Analog Input
The Analog Input (AI) function blocks produce the device outputs for Profibus. They utilize
the outputs from the Level TB (PV, SV1, SV2, … SVn) and then apply any required scaling
and quality checks. There are four AI blocks, which each use one of the TB outputs and
modify it to produce the Level, Space, Distance and Volume OUT values.
.
The input to the function block is one of the four Secondary Values, (SV4, SV5, SV6 and
SV7) of the Transducer Block Level. This input is fixed for each of the AI blocks. The
channel parameter is not utilized and the user cannot determine the input value to the
block.
The AI blocks also allow the input to be a simulated value instead of a TB OUT value. This
allows the AI block to be tested independently of the characteristics of the environment.
Linear conversion:
The scaling blocks can provide a linear conversion to any desired units.
1. The input value is normalized (Scaling Input)
2. The scaling output is applied.
3. This value is filtered using a first order filter based on a time constant provided by
the user.
4. The value is checked against the user parameterized warning and alarm limits.
(There is an upper and lower warning limit and an upper and lower alarm limit. The
unit of the limits corresponds to the unit of the output range. A hysteresis parameter
prevents toggling in the Status field of the OUT value.)
Note:
These AI OUTs are not the same as the TB outputs available to the LCD.:
Scaling
Input
Scaling
Output
Filter
Alarm
Limit
Checks
Failsafe
Target
Mode
OUT Value,
Actual Status
Mode
Ta
rg
et
M
od
e,
M
an
ual OUT Va
lu
e
Fa
ilsafe
Pa
ra
m
et
er
s,
Fa
ilsafe Outpu
t
Ala
rm L
im
its
,
Hys
ter
esis
Filt
er T
ime
Co
nst
ant
OUT S
ca
le
Sc
al
e I
n
Simu
lat
io
n
Enab
le
Sim
ulat
ion
Va
lue, S
tat
us
Va
lue, S
tat
us (f
ro
m
TB as select
ed b
y
Ch
an
nel P
ar
amet
er)
Ta
rg
et
M
od
e
Analog Input Function Block
Status & Mode
SITRANS LR 300.book Page 122 Monday, June 10, 2002 7:18 PM