Rievtech xLogic ELC Series User Manual page 131

Calculation rule

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.

If threshold On < Threshold Off, then Q = 1, falls:
On ≤ (actual value Ax - actual value Ay) < Off.
Reducing the input sensitivity of the analog comparator
You can delay the output of the analog 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
analog 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 analog block parameters, refer to the Analog 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 analog comparator
You can selectively delay the output of an analog 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 (=analog comparator output) is longer than the on-delay time.
Using this method, you will obtain a virtual hysteresis and reduce the input response to short signals.
Function block diagram
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