This function block detects six alarm conditions using the _LIM parameters (HI_LIM, HI_HI_LIM, LO_LIM, LO_LO_LIM, DV_LO_LIM, DV_HI_LIM). The result of the alarm detection uses the _ACT parameters that correspond to the appropriate _LIM parameter (HI_ACT, HI_HI_ACT, LO_ACT, LO_LO_ACT, DV_LO_ACT, DV_HI_ACT).
The value for all alarming is either wired to the IN parameter on the block, or referenced with IO_IN as an I/O path. Additionally, the SP value is used for deviation alarming.
When the ENABLE parameter is True(1), alarming is enabled. When ENABLE is False (0), alarming is disabled and all alarm XXX_ACT fields are cleared.
When the SCALE_ENABLE parameter is False, scaling is disabled. IN is expected in engineering units and written directly to PV.
When SCALE_ENABLE is True, IN is expected in percent. This percentage is applied to the range specified in IN_SCALE, which is in engineering units, to produce a PV in engineering units. The PV is then compared with the alarm limits, which are also in engineering units.