Output Q is set or reset depending on the difference of
the actual values Ax - Ay and the set thresholds. See the
following calculation rule.
Calculation rule
1. If threshold On ≥Threshold Off, then:
Q = 1, if (actual value Ax - actual value Ay) > On
Q = 0, if (actual value Ax - actual value Ay) ≤Off.
2. If threshold On < Threshold Off, then Q = 1, falls:
On ≤ (actual value Ax - actual value Ay) < Off.
Reducing the input sensitivity of the analogue
comparator
You can delay the output of the analogue comparator
selectively by means of the "on delay" and "off delay" SFBs.
By doing so, you determine that output Q is only set if the
input trigger length Trg (= output of the analogue
comparator) exceeds the defined-on delay time.
This way you can set a virtual hysteresis, which renders the
input less sensitive to short changes.
Particular characteristics to be noted when configuring
For help on analogue block parameters, refer to the
Analogue value processing section in xLogicsoft.
Setting the Par parameter
The gain and offset parameters are used to adapt the
sensors to the relevant application.
Example
In a heating control system, the supply Tv and return line
temperatures Tr are to be compared, for example with a
sensor at AI2.
A control signal is to be triggered (for example "heater
On") when the difference between the supply and return
line temperatures is greater than 15 °C. The control signal
is reset when the difference is less than 5 °C.
The process variable of the temperature is to be shown in
parameter assignment mode.
The thermocouples available have the following technical
data: -30 to +70 °C, 0 to 10 VDC.
Reducing the input response of the analogue
comparator
You can selectively delay the output of an analogue
comparator by means of the "On-delay" and "Off-delay"
special functions. With on-delay, output Q is only set if the
pulse width of the triggering signal at input Trg
(=analogue comparator output) is longer than the on-
delay time.
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