Instruction manual

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
Ta rge t
Mode
OUT Value,
Actual Status
Mode
Target Mod e,
Manual OUT
Value
Failsafe
Parameters,
Failsafe Output
Alarm Limits,
Hysteresis
Filter Time
Constant
OUT Scale
Scale In
Simulation
Enable
Simulation
Value, Status
Value, Status (from
TB as selected by
Channel Parameter)
Target Mod e
Analog Input Function Block
Status & Mode
SITRANS LR 300.book Page 122 Monday, June 10, 2002 7:18 PM