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MC OvErvIEW
The MC Elite Series controls modulates valves, motors,
variable speed drives, or boilers to accurately maintain a set
point based on a PID logic; temperature, pressure, vacuum,
or humidity. There are three different models, each provides
a different modulating signal. The MCA Elite modulates
current (4-20mA) or voltage motors. The MCP Elite
modulates 135Ω motors. The MCF Elite modulates floating
motors. In addition to the modulation, the MC Elite has an
output relay to activate a boiler, cooling unit, or a pump. Like
all Digi-Span Elites, the MC constantly displays the sensor's
value and the target set point. Additional control parameters
can also be displayed with the simple press of a button.
rEsEt rAtIO COnCEpt
The MC Elite Series can operate based on a temperature
set point or a pressure set point. If Temperature was set as
the Sensor Type, an Outdoor Reset option will be available
as the Control Mode. See "Control Mode" on page 11. The
Outdoor Reset gives the control the capability of changing the
heating Target set point based on the outdoor temperature.
See "Reset Ratio" on page 14.Because of the many different
physical characteristics of buildings and the type of radiation;
i.e., baseboard or radiant, the heat loss varies. In one
building, a 1° temperature change outdoors may require
a change of 1 degree in heating water temperature. For
another, it may require a change of 2, 3, or even 4 degrees
in order to gain the desired comfort level. The middle chart
shows the wide range of Reset Ratios available for the MC
Elite Series controls.
The installer fits the MC Elite control to a specific building
by adjusting the Reset Ratio curve. With curve #4
(2.00(O):1.00(S)) a 2° change in Outdoor temperature (O)
will change the circulating hot water Target (S) temperature
by 1 degree; at curve #11 (1.00(O):3.00(S)) an Outdoor
(O) change of 1 degree will change the Target (S) water
temperature by 3 degrees. Most buildings with baseboard
radiation require curve #6, 7, or 8. Radiant heat applications
usually require a lower curve.
BOILEr/COOLIng unIt OpErAtIOn
(MCA/MCP Only)
When the MCA/MCP Elite is set to modulate a heating/cooling unit, it starts when the EXT+ and EXT- terminals are
shorted. First, it will activate the heating/cooling unit output relay (Yellow wires) for the full Purge period. After the Purge
ends, the PID starts to modulate the output until the system sensor value reaches the Target set point.
On a reduction in the demand the MCA/MCP Elite modulates the output down. If no additional output is needed, the
control will modulate the unit to the off position (0% modulation). The output relay (Yellow Wires) will remain energized
for the Run-On period. In this case, the Run-On acts as a soft-off period for the boiler/cooling unit.
vALvE OpErAtIOn
(MCA/MCP Only)
When the MCA/MCP Elite is set to modulate a valve, it starts when the EXT+ and EXT- terminals are shorted. The
control will activate the output relay (Yellow Wires) and start to modulate the valve to get the system sensor value to the
Target set point. In many cases, the output relay will be controlling a pump.
On a reduction in the demand the MCA/MCP Elite will modulate the valve down. If no additional output is needed, the
control will modulate the valve to the off position (0% modulation). The output relay (Yellow Wires) will remain energized
for the Run-On period.
4
1:4 1:3
12 11
220
210
200
190
180
170
160
150
140
130
120
110
100
70
60
50
40
Outdoor Temperature (in °F)
Reset Ratio (Outdoor : Water)
Reset Ratio Curves
radiation type settings
radiation in Building
Radiators (Steel & Cast Iron)
Baseboard (Finned copper
tube& Cast Iron)
Radiant (High Mass/Concrete)
Radiant (Low Mass/Joists)
Fan Coils & Air Handlers
MC-Elite Installation and Operation Manual
1:2
1:1.5
10
9
8
1:1.25
7
1:1
6
1.25:1
5
1.5:1
4
2:1
3
3:1
2
4:1
1
8:1
30
20
10
0
-10
-20
reset ratio
Offset
0˚F
1.00 (O) : 1.00 (S)
0˚F
1.00 (O) : 1.00 (S)
-10˚F
4.00 (O) : 1.00 (S)
-10˚F
2.00 (O) : 1.00 (S)
20˚F
1.00 (O) : 1.00 (S)
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