Emerson VSG & VSSG Troubleshooting Guide download pdf (Page 29)

VSG/VSSG • Compact Logix PLC Manual •Vilter/Emerson • 35391CL

Setpoints on this screen:

· Discharge Pressure On/Off – The compressor will automatically cycle ON and OFF at the setpoints entered.

Discharge Pressure On/Off control is only active if the Compressor Control Via Discharge Pressure option

is selected on the Setup screen. If a compressor shutdown is desired on a discharge pressure drop and a

manual reset is required, set the OFF value below the Low Discharge Pressure Safety Trip value. This will

shut down the unit and a reset will be required to restart it.

· Discharge Pressure Capacity Increase – The capacity of the compressor will increase when suction pressure

is at or above the Increase ON setpoint, and the increase “off” timer has cycled. Capacity will continue to

increase until the Discharge Pressure Capacity Increase OFF setpoint is reached. If closer system control

is desired, set the ON and OFF setpoints at the same values. This will essentially eliminate any differential

between the ON and OFF setpoints.

· Discharge Pressure Capacity Decrease – The capacity of the compressor will decrease when discharge

pressure is at or below the ON setpoint, and the decrease “off” timer has cycled. Capacity will continue

to decrease until the Discharge Pressure Capacity Decrease OFF setpoint is reached. If closer system

control is desired, set the ON and OFF setpoints at the same values. This will essentially eliminate any

differential between the ON and OFF setpoints. While this setting is only available for adjustment on the

Control Setpoints screen when the Compressor Control Via Suction Discharge option is selected on the

Setup screen, it has an override effect when control is via process temperature as described below.

Discharge Pressure Control

Compressor Control Setpoints

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Emerson VSG & VSSG Troubleshooting Guide Page 29