FULTON Vantage VTG Series Installation And Operation Manual page 128

Lead / Lag Configuration 4

The PID compares the supply temperature to the supply setpoint and creates a control variable output based on
how far away from setpoint the loop temperature is and how long the loop temperature is away from it.

Proportional Band: The Proportional Band is a range defined around the set point. It is expressed as a
percentage of 300. In figure 25, a proportional band of 20% would equal a range of 60F. This would
indicate that the CV% output would equal 0% if the loop temperature was at setpoint and 100% if the
loop temperature was at 60F below setpoint.
o
A broad (Large) proportional band causes a more gradual response from the controller.
Typically, this will reduce setpoint overshoot.
o
A narrow (Small) proportional band causes a more rapid response from the ModSync. However
the system may tend to overshoot.
o
Because the ModSync will normally only have a single boiler on at low fire at a CV output of 0%,
Proportional control is rarely enough to get the loop temperature up to setpoint. As the
temperature begins to get to setpoint the CV begins to drop off to a point that the system will
stabilize at a point slightly below setpoint. For this reason it is recommended to use Integral
Time in combination with Proportional to achieve and maintain setpoint.

Integral Time: The Integral Time set is the amount of time, as calculated by the controller, required to
bring the loop temperature up to setpoint.
o
A broad (Large) Integral will cause a more gradual response from the controller.
o
A narrow (Small) Integral will cause a more rapid response. Note that if you set a short Integral
time, the function will respond very quickly and may overshoot the setpoint.

Derivative Time: Derivative time responds to the rate and direction of the change in the CV. Note
typically used in slow acting systems such as hydronic applications.

Manual Reset: Shifts where the PID begins its calculation prior to the lead boiler starting. This will
prevent the CV value from driving up prior to the lead boiler starting. It is recommended that the value be
equal to or greater than the lead boiler start deviation.
Questions? Call (315) 298-8510, or visit us online at www.fulton.com
Figure 25 – Lead / Lag Configuration Screen 3
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