Overview Difference limit switch

This block switches according to the difference between two values. If the difference W1 minus W2 reaches the switch-on difference, the output is set; if it falls to the switch-off difference or below, the output is reset. Minimum running time and minimum standstill time prevent excessive switching. A typical application is solar and heat exchanger logic: the pump runs as long as the collector is sufficiently warmer than the tank. The switch-off difference should be smaller than the switch-on difference.


Inputs

W1 Value 1 First value, for example the collector temperature.
W2 Value 2 Second value, for example the tank temperature.
FR Enable 0 switches the output off and blocks switching on. If the input is not assigned, the block is enabled. “Generate variables” deliberately does not create an address for this input, because a new address starts at 0 and would therefore block the block.



Outputs
AB Output Becomes 1 when the switch-on difference is reached and 0 again when the switch-off difference is reached or undercut.
DI Difference Current difference W1 minus W2.



Parameters
Switch-on difference Difference at which the output is switched on.
Switch-off difference Difference at which the output is switched off again. The distance to the switch-on difference acts as hysteresis.
Minimum running time (s) After switching on, the output stays set at least for this time, even if the switch-off difference has already been reached. 0 = off.
Minimum standstill time (s) After switching off, the output is not switched on again for at least this time. 0 = off.

See also: Limit switch, Measured value monitoring

See also common parameters of all function blocks.