tekmar 274 Boiler Control - Manual (Page 15)

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Energy Management System (EMS) Section G
The control can accept an external DC signal from an Energy
Management System (EMS) in place of the outdoor sensor.
The control converts the DC signal into the appropriate
boiler target temperature between 50°F (10°C) and 210°F
(99°C) based on the EMS Input Signal and Offset settings.
To use the external input signal, the EMS / Demands DIP
switch must be set to EMS.
An external signal is generated by applying a voltage
between 0 V (dc) and 10 V (dc) across the Out + and Com
– terminals (3 and 2). Voltages that exceed 10 V (dc) will
still be considered a 10 V (dc) signal.
Once voltage is applied, the EMS Input Signal pointer is
displayed in the LCD and the control calculates a boiler
target and closes the primary pump contact. The control
then activates the boiler(s), if required, to maintain the target
supply temperature.
If the EMS signal goes below the minimum voltage, the
EMS Input Signal pointer is turned off in the display. The
boiler target temperature is displayed as “– – –” to indicate
that there is no longer a call for heating. The primary pump
and boiler pumps operate as described in section I.
Input Signal
The control can accept either a 0 - 10 V (dc) signal or a
2 - 10 V (dc) signal. The External Input Signal setting must
be set to the proper setting based on the signal that is being
sent to the control.
0 - 10 V (dc) or 0 - 20 mA
When the 0 - 10 V (dc) signal is selected, an input voltage
of 1 V (dc) corresponds to a boiler target temperature of
50°F (10°C). An input voltage of 10 V (dc) corresponds
to a boiler target temperature of 210°F (99°C). As the
voltage varies between 1 V (dc) and 10 V (dc) the boiler
target temperature varies linearly between 50°F (10°C) and
210°F (99°C). If a voltage below 0.5 V (dc) is received the
boiler target temperature is displayed as “– – –” indicating
that there is no longer a call for heating.
A 0 - 20 mA signal can be converted to a 0 - 10 V (dc) signal
by installing a 500 Ω resistor between the Out + and Com
– terminals (3 and 2).
2 - 10 V (dc) or 4 - 20 mA
When the 2 - 10 V (dc) signal is selected, an input voltage
of 2 V (dc) corresponds to a boiler target temperature of
50°F (10°C). An input voltage of 10 V (dc) corresponds
to a boiler target temperature of 210°F (99°C). As the
voltage varies between 2 V (dc) and 10 V (dc) the boiler
target temperature varies linearly between 50°F (10°C) and
210°F (99°C). If a voltage below 1.5 V (dc) is received the
boiler target temperature is displayed as “– – –” indicating
that there is no longer a call for heating.
A 4 - 20 mA signal can be converted to a 2 - 10 V (dc) signal
by installing a 500 Ω resistor between the Out + and Com
– terminals (3 and 2).
CONVERSION TABLE 0 - 10
0 - 20 mA* 0 - 10 V (dc) Boiler Target
0 0 – – – (OFF)
2 1 50°F (10°C)
4 2 68°F (20°C)
6 3 86°F (30°C)
8 4 103°F (39°C)
10 5 121°F (49°C)
12 6 139°F (59°C)
14 7 157°F (69°C)
16 8 174°F (79°C)
18 9 192°F (89°C
20 10 210°F (99°C)
*Requires 500 Ω Resistor in Parallel
*Requires 500 Ω Resistor in Parallel
CONVERSION TABLE 2 - 10
4 - 20 mA* 2 - 10 V (dc) Boiler Target
0 0 – – – (OFF)
4 2 50°F (10°C)
6 3 70°F (21°C)
8 4 90°F (32°C)
10 5 110°F (43°C)
12 6 130°F (54°C)
14 7 150°F (66°C)
16 8 170°F (77°C)
18 9 190°F (88°C)
20 10 210°F (99°C)
Offset Setting in Adjust Menu
For external input operation, the boiler target (determined
from the external input signal) may be fine tuned. The
Offset setting is used to provide the fine tuning. The Offset
setting may be adjusted ±10°F. When set to 0°F, if the
temperature determined from the external signal is 140°F,
the boiler target will be 140°F. When set to +5°F and with
the same external signal represents 140°F, the boiler target
will be 145°F.
Example
Range
= 0 - 10 V (dc)
Input = 7 V (dc) 157°F (69°C)
Offset = +5°F (3°C) + 5°F (3°C)
Boiler Target = 162°F (72°C)
The minimum and maximum settings also apply for external
input operation. For example, if a boiler minimum of 140°F
is set and the external signal received represents 80°F, the
boiler target will be 140°F. The MIN segment will also be
displayed to indicate that a limiting condition is in effect.
This also applies for the MAX segment limit.
Whenever an external signal is used, the control can still
provide all DHW OR Setpoint functions.