Siemens LOGO!, Manual

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LOGO! functions
4.4 Special functions list - SF
LOGO!
Manual, 04/2011, A5E03556174-01
223
Function block diagram
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4.4.21 Analog watchdog
Short description
This special function saves the process variable of an analog input to memory, and sets the
output when the output variable exceeds or drops below this stored value plus a configurable
offset.
Symbol in LOGO! Wiring Description
Input En A positive edge (0 to 1 transition) at input En saves
the analog value at input Ax ("Aen") to memory and
starts monitoring of the analog range Aen - Δ
2
to
Aen+ Δ
1
Input Ax Input Ax is one of the following analog signals:
•
AI1 to AI8 (*)
• AM1 to AM6 (if 0BA6) or AM1 to AM16 (if 0BA7)
•
NAI1 to NAI32 (if 0BA7)
• AQ1 to AQ2
•
NAQ1 to NAQ16 (if 0BA7)
• Block number of a function with analog output
Parameter A: Gain
Range of values: ±10.00
B: Zero offset
Range of values: ±10,000
Δ
1
:Difference value above Aen:
on/off threshold
Range of values: 0-20,000
Δ
2:
Difference value below
Aen: on/off threshold
Range of values: 0-20,000
p: Number of decimals
Range of values: 0, 1, 2, 3
Retentivity:
/ = No retentivity
R = The status is retentive in memory
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Output Q Q is set/reset, depending on the stored analog value
and the offset.
* AI1...AI8: 0...10 V corresponds with 0...1000 (internal value).