© 2013
400_D - 09/13
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Boiler Maximum
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The 400 will operate the boiler so that the boiler
supply temperature will never exceed 210°F (99.0°C).
The highest allowed boiler target is the boiler design
tempe 10°F (5.5°C).
Boiler Type
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The 400 can operate either of the following types of
boilers:
One single-stage on-off boiler
One two-stage on-off boiler
Modulating boiler using a 0-10 V (dc) signal
Modulating boiler using a 4-20 mA signal
tekmar EMS signal (for use with multiple boiler
stagers)
EMS signal for Viessmann modulating boilers
On-Off Operation
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The 400 operates a single hot-water on-off boiler to
maintain the boiler target within a differential. The boiler
target is the average temperature and the boiler supply
temperature can fluctuate by 1/2 of the differential above
and below of the boiler target.
Modulation Boiler Operation
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The 400 can operate a single hot-water modulating
boiler using the Mod dc/mA output and the Boiler Stage
contact. Not all boilers require the use of the Boiler
Stage contact.
The control operates the boiler by first switching the boiler
stage contact to allow the modulating boiler to go through
the ignition sequence (the boiler stage contact may not
be required on all modulating boilers). A 0-10 V (dc) or 4-
20 mA analog signal is then used to modulate the boiler
firing rate starting from 50% (5 V (dc) or 12 mA signal) for
30 seconds.
After the 30 second delay has elapsed, the control will
then allow the boiler to modulate down to the minimum
modulation setting and hold it there for the Modulation Delay
time setting. The Modulation Delay setting is determined
by the boiler manufacturer. It is the amount of time that
the burner must operate before the internal boiler control
allows an external signal to operate the burner.
After the Modulation Delay has elapsed, the control uses
PID logic to change the boiler firing rate signal in order
to satisfy the boiler target temperature. When the firing
rate signal is reduced down to the Minimum Modulating
setting and the boiler supply temperature exceeds the
boiler target by 1/2 of the differential, the control will shut
off the burner.
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Minimum Modulation
The Minimum Modulation is the lowest signal the control
can send to modulate the boiler. This operates the boiler
at low fire.
Refer to the boiler manufacturer’s literature to deter-
mine the minimum output voltage V (dc) or current
(mA) that the boiler will successfully operate at.
For 0-10 V (dc):
Minimum Modulation =
Boiler’s Minimum Input Signal x 100%
10 V (dc)
For 4-20 mA:
Minimum Modulation =
Boiler’s Minimum Input Signal - 4mA x 100%
16 mA
Example:
A boiler requires a 1.8 V (dc) signal to fire the boiler at
low fire. The boiler can be modulated to 10 V (dc) where
it reaches high fire.
Minimum Modulation = 1.8 V x 100% = 18%
10 V
1.8 V (dc)
10 V (dc)
Control Rang
e
Boiler Rang
e
0 Vdc
18%
tekmar EMS Signal Operation
The 400 can provide a 0-10 V (dc) signal proportional to
the boiler target which is compatible with tekmar Boiler
Staging controls that accept an EMS input.
To use the tekmar EMS signal operation, the Boil Type
setting in the Adjust menu must be set to EMS1.
Viessmann EMS Signal
The 400 has a special 0-10 V (dc) signal proportional to
the boiler target that is designed to be compatible with
Viessmann Open Therm 0-10 V (dc) inputs.
To use the Viessmann EMS signal operation, the Boil
Type setting in the Adjust menu must be set to EMS2.
The signal is 0 V (dc) when the boiler is off. The voltage
is 2.2 V (dc) to provide a boiler target of 81°F (27°C),
up to maximum of 10 V (dc) to provide a boiler target of
176°F (80°C).
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