User Manual

LOGO! functions
4.4 Special functions list - SF
LOGO!
220 Manual, 04/2011, A5E03556174-01
Parameter p (number of decimals)
Applies only to Ax, Ay, On, Off and Δ values displayed in a message text.
Does not apply to the comparison of on and off values! (The compare function ignores the
decimal point.)
Timing diagram
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Functional description
The function fetches the analog values from the inputs Ax and Ay.
Ax and Ay are each multiplied by the value of the A (gain) parameter, and the value at
parameter B (offset) is then added to the relevant product, i.e.
(Ax • gain) + offset = actual value Ax or
(Ay • gain) + offset = actual value Ay.
The function forms the difference ("Δ") between the actual values Ax - Ay.
Output Q is set or reset, depending on difference of the actual values Ax - Ay and the set
thresholds. See the calculation rule below.
Calculation rule
● If the On threshold ≥ Off threshold, then:
Q = 1, if:
(actual value Ax - actual value Ay) > On
Q = 0, if:
(actual value Ax - actual value Ay) ≤ Off.
● If the On threshold < Off threshold, then Q = 1, if:
On ≤ (actual value Ax - actual value Ay) < Off.