Honeywell SDC Service Manual page 184

Hydraulic Components
7.3.4.10.1.2
NOTE
184
Integral action time Tn
The integral part (adjustment time) determines the dynamic
behaviour of the controller and thus the time required by the
controller to adjust for the actual control deviation. The adjustment
time is independent of the amount of deviation.
Example:
With a sudden flow temperature control deviation of 10 K (e.g.
when the system switches from reduced to daytime operation)
and an I-part setting of 7 minutes, the controller will adjust for the
new (10 K higher) flow temperature after the set time.
The adjustment time can be determined through the Ziegler-
Nichols method. The mixed heating circuit is closed, initially, and
the heat generator is taken to the maximum temperature for the
heating circuit concerned. As soon as half of all consumers at the
circuit to be measured have been opened, the mixer is fully
opened from cold condition (room temperature) by means of the
relay test function. The heat-up curve, i.e. the temperature
progression over time following this action, shows an inflection
point. The crossing of the tangent through that point and the time
axis is the delay time. This value multiplied by the factor 3.3 is the
optimum integral action time for this heating circuit.
SDC / DHC
EN2H-0221GE51 R0812