8
Auto Differential
Auto Differential is only available when using PID stag-
ing.
If Auto Differential is selected, the control automatical-
ly determines the best differential as the load changes,
thereby improving efficiency. During light loads, the dif-
ferential is increased to allow longer on and off times
to reduce the potential for short-cycling. During large
loads, the differential is narrowed thereby improving
comfort in heating spaces by reducing temperature
swing.
Fig. 16: Auto Differential
Staging Mode (STGMODE)
The Controller can operate up to four stages in order
to supply the required target temperature. The method
of staging used by the Controller is either P (propor-
tional) or PID (proportional, integral & derivative), and
is selected using the STGMODE item in the adjust
menu.
Proportional (P)
Proportional staging is based on manually-adjusted
settings that determine when the next stage is
required to turn on. These manual settings are based
on temperature and time. The interstage differential
sets the temperature drop at which the next stage
turns on. However, in order for a stage to fire, both the
“interstage delay on” and “minimum off” times must
first elapse.
Fig. 17: Proportional Staging
Code Descriptions
Heater Differential (DIFF)
A heat source must be operated with a differential in
order to prevent short cycling. The heater differential is
divided around the heater target temperature. The
first-stage contact will close when the water tempera-
ture at the operating sensor is 1/2 of the differential
setting below the heater target temperature, and will
open when the water temperature at the operating
sensor is 1/2 of the differential setting above the
heater target temperature. The remaining stages will
operate sequentially based on the staging mode
selected.
Manual Differential
The differential can be manually set using the DIFF
setting in the Adjust menu.
Fig. 15: Fixed Differential
