Carrier 17/19EX - Manual (Page 93)

Demand Limit Control, Option (Requires Optional 8-Input Module)
The demand limit may be externally controlled with a 4 to 20 mA signal from an energy
management system (EMS). The option is set up on the Config table. When enabled, the
control is set for 100% demand with 4 mA and an operator configured minimum demand set
point at 20 mA.
The Demand Reset input from an energy management system is hardwired into the number
one, 8-input module. The signal may be internally powered by the module or externally
powered. If the signal is externally powered, the signal is wired to terminals J1-1(+) and J1-2(–).
If the signal is internally powered, the signal is wired to terminals J1-3(+) and J1-2(–). When
enabled, the control is set for 100% demand with 4 mA and an operator configured minimum
demand set point at 20 mA.
Surge Prevention Algorithm
This is an operator configurable feature which can determine if lift conditions are too high for
the compressor and then take corrective action. Lift is defined as the difference between the
pressure at the impeller eye and the impeller discharge. The maximum lift that a particular
impeller wheel can perform varies with the gas flow across the impeller, and the size of the
wheel.
The algorithm first determines if corrective action is necessary. This is done by checking 2
sets of operator configured data points, which are the MINIMUM and the MAXIMUM Load