4
Heat-Timer Corp.
059040-00 C
ModulatIng logIc overvIeW
The Modulation PID logic provides the capability of controlling multiple modulating current or voltage boilers to maintain the system
target temperature. When heat is required, the control PID will activate the lead boiler and start its purge. See "Purge Delay" on
page 23. This will be followed by the initiation of its modulation at the Ignition %. See "Ignition %" on page 30. After the Purge period
and when additional heat is needed, the control shall start to increase the lead boiler modulation until the Modulation Start % has
been reached. See "Modulation Start %" on page 30. That shall be followed by the lag boiler purge initiation. The lead boiler shall
resume its modulation while the lag boiler is in purge until the lead boiler reaches full fire (100% modulation). Any additional heat
requirements will trigger the control to increase the lag boiler modulation.
When the Mini-MOD PID requires reduced output, it will reduce the modulation of the lag boiler until it reaches its Ignition %. That
shall be followed by the reduction of modulation of the lead boiler until it reaches 40% percent of the Modulation Start %. This shall
trigger the control to turn off the lag boiler. The control will keep reducing the lead boiler modulation until it reaches its Ignition %.
If the Last Stage Hold was activated, the control will hold the lead boiler at the Ignition % until the System Temperature exceeds the
Target Set Point by the Last Stage hold setting. See "Last Stage Hold" on page 24.
