back alarm condition because the Lead/Lag control should have already generated an alarm if something was wrong and the standby AHU was called into action. Be sure to check the Alarming Enabled box if you want this alarm to be reported back to the PRISM screen or to a Remote Pager.
Analog Input #2 - #7 The remaining inputs are not required for this program.
Relay Output #1 Programming ( Used for Lead AHU Enable Signal )
This relay was chosen to be the Lead control output and was connected to AHU #1. Either AHU could have been selected as AHU #1, this was an arbitrary decision. The Supply Air was selected as the Control Source and the Proof Setpoint was set to 60.0°F. The AHU’s will change the Lead every 24 Hours and if the Supply Air rises above 60° for more than 60 seconds, it will be considered to be in failure mode and the Lag AHU will be activated. Also, an alarm will be generated so that an immediate service call can be made to determine the cause of failure. If both units should happen to fail, there is no further redundant capabilities and service personnel will need to correct the problems and then Reset the control from the Alarm Indicator Screen (shown later in this section).
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