Demand Limit Control, Option (Requires Optional 8-Input Module )
The demand lim it may be exte rnally controlled with a 4 to 20 mA signa l from an ene rgy
management system (EMS). The option is set up o n the Config table. When enabled, the
control is set for 100% dema nd with 4 mA and an operator c on figured minimum dema nd set
point at 20 mA.
The Demand Reset input from an energy management system is hardwired into the number
one, 8-input mod ule. The sig nal may be int ernally powered by the module or externally
powered. If the sign al is externally power ed, the signal is wire d to terminals J1-1(+ ) and J1-2(–).
If the signal is internal ly powered, the signal is wired to terminals J1-3 (+) and J1-2(–). When
enabled, the control is s et for 100% demand with 4 mA and an operator configured minimum
demand set point at 20 mA.
Surge Prevention Algorithm
This is an opera tor configurable feature which c an determine i f lift conditions are too high f or
the compressor and the n ta ke corrective action. Lift is defined as the diff erence between the
pressure at the impeller ey e and the impeller disch arge. The maximum lift that a particular
impeller wheel can per fo rm varies with the gas fl ow ac r o ss the impeller, and the size of the
wheel.
The algorithm first det ermines if correctiv e ac t ion is necessary. This is do ne by checking 2
sets of operator configured data points, which are the MINIMUM and the MAXIMUM Load