EXAMPLES CARE CONTROL ICONS74-5577–33 (US) 246EN2B-0184 GE51 R0518 (Europe)AttenuatorPurpose In many applications, the desired calculation is not based on a momentary valuesuch as outdoor air temperature but is averaged over an hour. Instead of an exactmean value, you can calculate a good approximation by “attenuating” the value. Forexample, the following formula approximates outdoor air temperature:Approx. OATnew = INT(MomentaryOAT - Approx.OATold)INT stands for an integral function.Control Icons Use the SWI, MAT, and DIF control icons.Example The following diagram shows the control loop and switching table setup for thisapplication.The closed loop control symbol DIF calculates the differential between themomentary outdoor temperature and the old approximate outdoor temperature. TheMAT symbol provides a formula to integrate the difference (INT function). Theintegral function uses TI (reset time) equal to 60 minutes and has a limit value (LIM)of 50C (122F).Note that the “difference” pseudopoint is an analog flag. It does not have to beavailable for operator display.The MAT output calculates the appropriate outdoor temperature. During equipmentstart-up, actual outdoor temperature overrides the calculated temperature. Forexample, start-up maintains 20 seconds on zero, then follows with an approximationof the outdoor temperature. Before this, the approximate outdoor temperatureequals the momentary outdoor temperature. This action correctly initializes theintegral function.To use the STARTUP point, see Appendix B: Startup User Address.
