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Understanding Class A, Class B, and Class C Inputs in Enbase
Learn how Class A, Class B, and Class C inputs determine when compressor safety shutdown Tags become armed in the Enbase Compressor Control Panel.
The Enbase Compressor Control Panel uses Class A, Class B, and Class C input classes to determine when Safety Shutdown Tags become armed and are allowed to trigger a shutdown fault.
The input class describes the arming behavior of the Tag. It is separate from the Shutdown Type, which determines what the panel does if the Tag enters a fault state.
Class A: Immediate
Class A inputs are armed immediately. If a Class A input enters a configured fault condition, it can cause a shutdown fault without waiting for a startup timer or for the equipment to reach steady state.
One example is High Cylinder Discharge Temperature because a high cylinder temperature may require immediate protection once the input is in a fault state.
Class B: Timer
Class B inputs are not armed until their configured arming timer expires. This allows the compressor time to move through startup conditions before certain inputs are allowed to cause a shutdown fault.
One example is Low Suction Pressure. During startup, suction pressure may not yet be at its normal operating condition, so the input can remain unarmed until the appropriate timer has expired.
Class C: Steady State
Class C inputs can begin in a faulted condition without immediately triggering a shutdown. Once the input moves out of the fault condition, or its corresponding timer expires, the input becomes armed.
One example is Low Engine Speed. The engine needs time to start and reach an acceptable speed before a low speed condition should be treated as a shutdown fault.
Why Input Classes Matter
Input classes help prevent inappropriate shutdowns during normal startup while still protecting the compressor once the required operating conditions have been reached.
When reviewing a Safety Shutdown Tag, the Input Class helps explain when the Tag becomes active for shutdown protection. The Shutdown Type determines whether a resulting fault performs an emergency shutdown, a standard shutdown, or no shutdown.
Before Changing an Input Class
Changing the Input Class of a Safety Shutdown Tag can affect when the compressor is protected from a fault condition. Contact Enbase Support if you are unsure whether an Input Class or its associated timer should be changed.