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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).