Liebert TM-10098 service manual Proportional P Control, Proportional + Integral PI Control

iCOM Controls Training and Service Manual

more efficient and precise for most applications, but system performance based on room conditions is not as predictable as standard approaches that use a fixed equation.

The Liebert Intelligent Control includes rules that significantly enhance the performance of the system, both from a standpoint of precision control and system reliability.

Rules are included that:

•Cause the control to ignore very small or temporary temperature/ humidity deviations. This eliminates unnecessary control adjustments that contribute to control instability.

•Help limit the frequency of control adjustments thus extending the life of system components that are susceptible to mechanical wear or cycling.

•Recognize undesired modes of control operation such as hunting, and make adjustments to the control response to eliminate them.

•Estimate the present load on the system and then tend to force the control output to the appropriate state.

•Recognizes conditions, which indicate a large load change and allows the control to temporarily respond more quickly than normal.

•Cause the control to anticipate the need for reheat during dehumidification and activates reheats when overcooling occurs.

Proportional (P) Control

The proportional control is the standard control method that maintains the room at a temperature proportional to the load. The temperature maintained increases as the room load increases. At full load the room would be controlled at a temperature equal to the temperature set point (TSP) plus ½ of the temperature proportional band (PB). The operator programmed inputs are the temperature set point (TSP) and temperature proportional band (PB) adjustments. The operator may also program a temperature dead band (DB) adjustment.

Proportional + Integral (PI) Control

The PI control combines two (2) individual terms to determine the control output for a given set of conditions. Note that PI control is used only for temperature. If PI control is selected, the humidity control will be in percent relative humidity (%RH).

The proportional (P) term is determined by the difference between the current temperature and the control set point. This term is expressed in % cooling (heating desired for each degree above (below) the set point. It is adjustable from 0% to 100% per degree. The purpose of this term is to adjust the control output for any deviation between the current temperature and the control set point.

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