ALPHABETIC REFERENCE EXCEL CARE CONTROL ICONS74-5577–33 (US) 80EN2B-0184 GE51 R0518 (Europe)LEAD-LAGFunction This XFM controls two devices with lead-lag logic.I/O Dialog BoxInputs Ld Lead Device, 0 for first device, 1 for secondLdE Lead Device Enable, 1 to Enable, 0 to DisableLdF Lead Device Failure, 0 is normal, 1 is failedLgE Lag Device Enable, 1 to Enable, 0 to DisableSt1 Device 1 Status, 1 is On, 0 is OffSt2 Device 2 Status, same as St1The lead enable input point, LdE, is a connection to a digital signal calling forstart-up of the lead device. A value of 1 turns the lead device on. A value of 0 turns itoff.The lag enable input point, LgE, is a similar connection for turning on and off the lagdevice. The connection should be made from an operator calling for the lag deviceto be either on or off.Outputs Ss1 Device 1 Start/StopSs2 Device 2 Start/StopLdF Lead Device FailureThe point LdF indicates lead device failure. It is meant to be passed back into thissubmodule or put through some other logic, then passed back into the submodule. Ifthe devices being controlled by this submodule are stand-alone or are meant to bebacked up individually you can pass the output LdF directly to the input LdF througha VD point. If the devices are part of a system which is to fail if any component in thesystem fails, there will be several module calls to the submodule and you will needto look at all of these LdF points and create one new VD point to pass back into theappropriate submodules.When the LdE point is turned on, the lead device is started and a timer delay isinitiated. Time is set at Parameter P1. If any time after this time expires, the leaddevice status is not true, the LdF point turns on. If the Ld point is changed while theLdE is on, the LdF is reset to False and a new time delay is initiated. When the LdEis turned Off, the Ss points that were on continue to run for the time set atParameter P2.
