Series S Solid-State Staging Controller Instruction Manual
14
Series S Solid-State Staging Controller Instruction Manual
15
Reset Ratio
The reset ratio expresses the amount of change in
the heating medium control point caused by a change
in outdoor temperature. It is the ratio of outdoor
Change to heating medium control point change.
Notice that this is an inverse ratio: when outdoor
temperature goes down, the control point goes up.
Selecting The Reset Ratio
The reset ratio should be selected to provide a
complete range of heating medium temperatures
when the outdoor temperature goes from 70ºF to
the outdoor design temperature. Typical reset ratios
for a number of different types of heating systems
are given in TABLE 1. These figures are intended
to provide the installer with a starting point on
installations where the reset ratio is not specified.
Further adjustments may be necessary depending on
the requirements of a particular system.
Operation
The 5002 sensor measures the outdoor temperature.
A change to in and outdoor air temperature causes
a resistance change in the Thermistor element of
the sensor. This resistance change unbalances the
bridge circuit of the reset controller. The effect of the
unbalance is to offset the heating medium control
point. The amount of offset in the relation to outdoor
change is determined by the setting of the Reset
Ratio knob. The action of the controlled equipment
compensates for the bridge unbalance by supplying
more or less heat to the controlled space.
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